Organic Solar Cells E-Book

• Herausgeber: Wiley-VCH GmbH
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1333

Veröffentlichungsjahr: 2022

Beschreibung

Organic Solar Cells

A timely and singular resource on the latest advances in organic photovoltaics

Organic photovoltaics are gaining widespread attention due to their solution processability, tunable electronic properties, low temperature manufacture, and cheap and light materials. Their wide range of potential applications may result in significant near-term commercialization of the technology.

In Organic Solar Cells: Materials Design, Technology and Commercialization, renowned scientist Dr. Liming Ding delivers a comprehensive exploration of organic solar cells, including discussions of their key materials, mechanisms, molecular designs, stability features, and applications. The book presents the most state-of-the-art developments in the field alongside fulsome treatments of the commercialization potential of various organic solar cell technologies.

The author also provides:

• Thorough introductions to fullerene acceptors, polymer donors, and non-fullerene small molecule acceptors
• Comprehensive explorations of p-type molecular photovoltaic materials and polymer-polymer solar cell materials, devices, and stability
• Practical discussions of electron donating ladder-type heteroacenes for photovoltaic applications
• In-depth examinations of chlorinated organic and single-component organic solar cells, as well as the morphological characterization and manipulation of organic solar cells

Perfect for materials scientists, organic and solid-state chemists, and solid-state physicists, Organic Solar Cells: Materials Design, Technology and Commercialization will also earn a place in the libraries of surface chemists and physicists and electrical engineers.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Preface

1 Conjugated Polymer Donors for Organic Solar Cells

1.1 Introduction

1.2 LBG Polymers

1.3 MBG Polymers

1.4 WBG Polymers

1.5 Summary and Outlook

References

Note

2

p

‐Type Molecular Photovoltaic Materials

2.1 Introduction

2.2 p‐Type Molecular Photovoltaic Materials Used in Vacuum‐Deposited Solar Cells

2.3 p‐Type Molecular Photovoltaic Materials Used in Solution‐Processed Solar Cells

2.4 Current Progress on Small‐Molecule Solar Cells with Nonfullerene Acceptors

2.5 Summary and Outlook

References

3 Fullerene Acceptors

3.1 Introduction

3.2 Fullerene Acceptors for Organic Solar Cells

3.3 Summary

References

4 Non‐fullerene Small‐Molecule Acceptors for Organic Solar Cells

4.1 Molecular Design Principles

4.2 PDI‐Based SMAs

4.3 A–D–A‐Type SMAs

4.4 A–DA′D–A–Type SMAs

References

5 Electron‐Donating Ladder‐Type Heteroacenes for Photovoltaic Applications: From Polymer Donor Materials to Small‐Molecule Acceptor Materials

5.1 Introduction

5.2 D–A Copolymers Based on Ladder‐Type Heteroacenes

5.3 A–D–A NFAs Based on Ladder‐Type Heteroacenes

5.4 Conclusions and Outlook

References

Note

6 Chlorinated Organic Solar Cells

6.1 Introduction

6.2 Chlorination Versus Fluorination: A Comprehensive Study

6.3 Recent Advances in Chlorinated Semiconductors

6.4 Conclusion and Outlook

References

7 Polymer–Polymer Solar Cells: Materials, Device, and Stability

7.1 Introduction

7.2 The Device Structure and Basic Principles of All‐PSCs

7.3 Materials Design Toward Efficient All‐PSCs

7.4 Device Performance and Stability of All‐PSCs

7.5 Conclusion and Outlook

References

8 Organic Solar Cells with High Open‐Circuit Voltage >1 V

8.1 Introduction

8.2 n‐Type Small‐Molecule Acceptors

8.3 n‐Type Polymers

8.4 Conclusion and Outlook

References

9 Single‐Component Organic Solar Cells

9.1 Introduction

9.2 Single‐Component Conjugated Materials for SCOSCs

9.3 Morphological Studies of the Photo‐Active Layers in the SCOSCs

9.4 Perspective and Challenges of SCOSCs

References

10 Tandem Organic Solar Cells: Recent Progress and Challenge

10.1 Introduction

10.2 Active Layer Materials in Tandem OSCs

10.3 Interconnecting Layer Materials

10.4 The Semi‐Empirical Analysis of Tandem OSCs

10.5 Conclusion and Outlook

Acknowledgments

References

11 Large‐Area Flexible Organic Solar Cells

11.1 Introduction

11.2 Material Requirements for Large‐Area Flexible Organic Solar Cells

11.3 Flexible Electrodes and Substrates

11.4 Large‐Area Flexible Device Fabrication

11.5 Efficiency Loss in Large‐Area Devices and Modules

11.6 Conclusion and Outlook

References

Note

12 Organic Photovoltaics for Indoor Applications

12.1 Introduction

12.2 The Characteristics of Indoor Lighting Sources

12.3 Testing System and Parameters for Indoor OPVs

12.4 Research Progresses

12.5 Summary and Prospective

References

13 Interfacial Design for Efficient Organic Solar Cells

13.1 Introduction

13.2 The Mechanism and Effect of Interfacial Design

13.3 Anode Interlayer Materials

13.4 Cathode Interlayer Materials

13.5 Conclusion and Outlook

References

14 Morphological Characterization and Manipulation of Organic Solar Cells

14.1 Introduction

14.2 Morphological Characterization of Organic Solar Cells

14.3 Morphological Manipulation of Organic Solar Cells

14.4 Conclusion

References

15 Operational Stability and Built‐in Potential in Organic Solar Cells

15.1 Introduction

15.2 Bimolecular Recombination in Organic Solar Cells

15.3 Metal/Organic Interfacial Exciton Dissociation in Organic Solar Cells

15.4 Improvement of Charge Collection and Performance Reproducibility

15.5 Effect of Built‐in Potential on Stability of Organic Solar Cells

15.6 Summary

Acknowledgment

References

16 Voltage Losses and Charge Transfer States in Donor–Acceptor Organic Solar Cells

16.1 The Origin of Voc of Solar Cells

16.2 Voc of Organic Solar Cells

16.3 Strategies to Reduce Vnr and Vr in Organic Solar Cells

16.4 Summary

Acknowledgments

References

17 Stability of Organic Solar Cells: From Fullerene Derivatives to Non‐fullerene Acceptors

17.1 Introduction

17.2 Factors Limiting the Stability of Organic Solar Cells

17.3 Stability Evaluation Protocols

17.4 Progress in Developing Stable Organic Solar Cells

17.5 Recent Progress on Developing Organic Solar Cells with Excellent Stability

17.6 Summary and Outlook

References

18 Potential Applications of Organic Solar Cells

18.1 Introduction

18.2 Building‐Integrated OSCs

18.3 Wearable‐Integrated OSCs

18.4 OSCs‐Integrated Energy Storage System

18.5 Other Applications

18.6 Conclusion and Outlook

References

Index

Wiley End User License Agreement

List of Tables

Chapter 1

Table 1.1 Optoelectronic properties and device performances of P1–P12.

Table 1.2 Optoelectronic properties and device performances of P13–P20.

Table 1.3 Optoelectronic properties and device performances of P21–P24.

Table 1.4 Optoelectronic properties and device performances of P25–P31.

Table 1.5 Optoelectronic properties and device performances of P32–P39.

Table 1.6 Optoelectronic properties and device performances of P40–P48.

Table 1.7 Optoelectronic properties and device performances of P49–P52.

Table 1.8 Optoelectronic properties and device performances of P53–P67.

Table 1.9 Optoelectronic properties and device performances of P68–P78.

Table 1.10 Optoelectronic properties and device performances of P79–P81.

Table 1.11 Optoelectronic properties and device performances of P82–P96.

Table 1.12 Optoelectronic properties and device performances of P97–P111.

Table 1.13 Optoelectronic properties and device performances of P112–P119.

Table 1.14 Optoelectronic properties and device performances of P120–P128.

Table 1.15 Optoelectronic properties and device performances of P129–P143.

Table 1.16 Optoelectronic properties and device performances of P144–P154.

Table 1.17 Optoelectronic properties and device performances of P155–P166.

Table 1.18 Optoelectronic properties and device performances of P167–P172.

Table 1.19 Optoelectronic properties and device performances of P173–P181.

Table 1.20 Optoelectronic properties and device performances of P182–P189.

Table 1.21 Optoelectronic properties and device performances of P190–P202.

Table 1.22 Optoelectronic properties and device performances of P203–P215.

Table 1.23 Optoelectronic properties and device performances of P216–P224.

Table 1.24 Optoelectronic properties and device performances of P225–P230.

Table 1.25 Optoelectronic properties and device performances of P231–P241.

Table 1.26 Optoelectronic properties and device performances of P242–P254.

Table 1.27 Optoelectronic properties and device performances of P255–P261.

Table 1.28 Optoelectronic properties and device performances of P262–P284.

Table 1.29 Optoelectronic properties and device performances of P285–P301.

Table 1.30 Optoelectronic properties and device performances of P302–P323.

Table 1.31 Optoelectronic properties and device performances of the WBG poly...

Chapter 2

Table 2.1 Performance of the OT‐based SMDs.

Table 2.2 Performance of the D–A–A′‐type SMDs.

Table 2.3 Performance of the BODIPY‐based SMDs.

Table 2.4 Performance of the SMDs mentioned in this part.

Table 2.5 Performance of the OT‐based A–D–A‐type SMDs.

Table 2.6 Performance of the BDT‐based A–D–A‐type SMDs.

Table 2.7 Performance of the DTS‐based A–D–A‐type SMDs.

Table 2.8 Performance of the DTP‐based A–D–A‐type SMDs.

Table 2.9 Performance of the DTS‐based D1‐A‐D2‐A‐D1‐Type SMDs.

Table 2.10 Performance of the BDT‐based D1‐A‐D2‐A‐D1‐Type SMDs.

Table 2.11 Performance of the IDT‐based D1‐A‐D2‐A‐D1‐type SMDs.

Table 2.12 Performance of the Por‐based SMDs.

Table 2.13 Performance of the SMDs mentioned in this part.

Table 2.14 Performance of the NFA‐based SMSCs mentioned in this part.

Chapter 3

Table 3.1 Performance of pristine C

60

‐ and C

70

‐based solar cells.

Table 3.2 Performance of fullerene‐monoadduct‐acceptors‐based solar cells.

Table 3.3 Performance of fullerene‐bisadduct‐acceptors‐based solar cells.

Table 3.4 Performance of fullerene‐multiadduct‐acceptors‐based solar cells.

Table 3.5 Performance of unconventional‐fullerene‐acceptors‐based solar cell...

Chapter 4

Table 4.1 Optical bandgap, energy levels, and photovoltaic parameters for PD...

Table 4.2 Optical bandgap, energy levels, and photovoltaic parameters for PD...

Table 4.3 Optical bandgap, energy levels, and photovoltaic parameters for PD...

Table 4.4 Optical bandgap, energy levels, and photovoltaic parameters for A–...

Table 4.5 Optical bandgap

, energy levels, and photovoltaic parameters for A–...

Table 4.6 Optical bandgap, energy levels, and photovoltaic parameters for A–...

Table 4.7 Optical bandgap, energy levels, and photovoltaic parameters for A–...

Table 4.8 Optical bandgap, energy levels, and photovoltaic parameters for A–...

Table 4.9 Optical bandgap, energy levels, and photovoltaic parameters for A–...

Chapter 5

Table 5.1 Summary of bandgaps, energy levels, and photovoltaic performances ...

Table 5.2 Summary of bandgaps, energy levels, and photovoltaic performances ...

Table 5.3 Summary of bandgaps, energy levels, and photovoltaic performances ...

Table 5.4 Summary of bandgaps, energy levels, and photovoltaic performances ...

Table 5.5 Summary of bandgaps, energy levels, and photovoltaic performances ...

Table 5.6 Summary of bandgaps, energy levels, and photovoltaic performances ...

Table 5.7 Summary of bandgaps, energy levels, and photovoltaic performances ...

Table 5.8 Summary of bandgaps, energy levels, and photovoltaic performances ...

Chapter 6

Table 6.1 Optical properties and HOMO of chlorinated polymers and device per...

Table 6.2 Electronic and photovoltaic performance of polymer donor‐based chl...

Table 6.3 Electronic and photovoltaic performance of polymer donor‐based chl...

Table 6.4 Electronic and photovoltaic performance of small‐molecule acceptor...

Chapter 8

Table 8.1 Summary of the energy levels and device characteristics of fullere...

Table 8.2 Summary of the energy levels and device characteristics of PDI and...

Table 8.3 Summary of the energy levels for BT based NFAs and the device char...

Table 8.4 Summary of the energy levels for BTA based NFAs and the correspond...

Table 8.5 Summary of the energy levels for the active layer in all‐PSCs and ...

Chapter 10

Table 10.1 Photovoltaic performance of fullerene‐based tandem organic solar ...

Table 10.2 Photovoltaic performance of NFA‐based tandem organic solar cells ...

Chapter 11

Table 11.1 The performance of thick‐film polymer‐fullerene binary devices.

Table 11.2 The performance of thick‐film polymer‐non‐fullerene binary solar ...

Table 11.3 The performance of thick‐film ternary organic solar cells.

Table 11.4 The performance of all‐polymer‐based system with thick films.

Chapter 12

Table 12.1 The photovoltaic performance of the devices mentioned in this cha...

Chapter 15

Table 15.1 Summary of the parameters obtained for a set of structurally iden...

Table 15.2 Values of bimolecular recombination lifetime

τ

B

and dispersio...

Table 15.3 The performance of the inverted OSCs made with the Al‐modified Zn...

Table 15.4 The performance of inverted OSCs made with the Al‐modified ZnO an...

Chapter 17

Table 17.1 Summary of testing guidelines for the different stress conditions...

Chapter 18

Table 18.1 Lifecycle energy in MJ per kW h

el

, energy payback time (EPBT) in ...

List of Illustrations

Chapter 1

Figure 1.1 (a) UV–vis–

near‐infrared

(

NIR

) absorption of different band...

Figure 1.2 The chemical structures of BT and its derived building blocks....

Figure 1.3 Chemical structures of the BT‐derived conjugated polymers P1–P12....

Figure 1.4 Chemical structures of the NT‐derived conjugated polymers P13–P20...

Figure 1.5 Chemical structures of the BT‐derived conjugated polymers P21–P24...

Figure 1.6 (a) The chemical structure of isoindigo. (b) The aromatic (left) ...

Figure 1.7 Chemical structures of the isoindigo‐based conjugated polymers P2...

Figure 1.8 Chemical structures of the isoindigo‐based conjugated polymers P3...

Figure 1.9 Chemical structures of the isoindigo‐derived conjugated polymers ...

Figure 1.10 Chemical structures of the isoindigo‐derived polymers P49–P52....

Figure 1.11 The chemical structure of DPP and its derived building blocks....

Figure 1.12 Chemical structures of the DPP polymers P53–P64.

Figure 1.13 Bright field

transmission electron microscopy

(

TEM

) images (1.2 ...

Figure 1.14 Bright field TEM images of the P65‐P67:PC

71

BM blends for differe...

Figure 1.15 Chemical structures of the DPP polymers P68–P78.

Figure 1.16 Chemical structures of the DPP polymers P79–P81.

Figure 1.17 The chemical modification strategy of BDT‐BT‐based polymers.

Figure 1.18 Chemical structures of the BT‐derived copolymers P82–P96.

Figure 1.19 Chemical structures of the BT‐derived copolymers P97–P111.

Figure 1.20 Chemical structures of the BT‐derived copolymers P112–P119.

Figure 1.21 Chemical structures of the BT‐derived copolymers P120–P128.

Figure 1.22 Chemical structures of the BT‐derived copolymers P129–P143.

Figure 1.23 The chemical structure of quinoxaline and the structural modific...

Figure 1.24 Chemical structures of the Qx‐derived copolymers P144–P154.

Figure 1.25 Chemical structures of the Qx‐derived copolymers P155–P166.

Figure 1.26 Chemical structures of the Qx‐derived copolymers P167–P172.

Figure 1.27 Chemical structures of the TPD‐derived copolymers P173–P181.

Figure 1.28 Chemical structures of the TPD‐derived copolymers P182–P189.

Figure 1.29 Chemical structures of the TPD‐derived copolymers P190–P202.

Figure 1.30 The aromatic form and quinoidal form of BDT‐TT based polymers....

Figure 1.31 Chemical structures of the TT‐derived copolymers P203–P215.

Figure 1.32 Chemical structures of the TT‐derived copolymers P216–P224.

Figure 1.33 Chemical structures of the TT‐derived copolymers P225–P230.

Figure 1.34 Chemical structures of the PT‐derived copolymers P231–P241.

Figure 1.35 Chemical structures of the benzodithiophene‐

alt

‐thiophene‐derive...

Figure 1.36 Chemical structures of the BT‐derived polymers P255–P261.

Figure 1.37 Chemical structures of the benzotriazole‐derived polymers P262–P...

Figure 1.38 Chemical structures of the polymer donors based on thiazole, pyr...

Figure 1.39 Chemical structures of the BDD derived polymers P302–P323.

Figure 1.40 Chemical structures of the WBG polymer donors of P324–P334.

Chapter 2

Figure 2.1 Molecular structures of the OT‐based SMDs.

Figure 2.2 Molecular structures of the D–A–A′‐type SMDs.

Figure 2.3 Molecular structures of the BODIPY‐based SMDs.

Figure 2.4 Molecular structures of other popular vacuum‐deposited SMDs.

Figure 2.5 Molecular structures of the OT‐based A–D–A‐type SMDs.

Figure 2.6 Molecular structures of the BDT‐based A–D–A‐type SMDs.

Figure 2.7 Molecular structures of the DTS‐based A–D–A‐type SMDs.

Figure 2.8 Molecular structures of the DTP‐based A–D–A‐type SMDs.

Figure 2.9 Molecular structures of the DTS‐based D1‐A‐D2‐A‐D1‐type SMDs.

Figure 2.10 Molecular structures of the BDT‐based D1‐A‐D2‐A‐D1‐type SMDs....

Figure 2.11 Molecular structures of the IDT‐based D1‐A‐D2‐A‐D1‐type SMDs....

Figure 2.12 Molecular structures of the Por‐based SMDs.

Figure 2.13 Molecular structures of the SMDs mentioned in this part.

Figure 2.14 Molecular structures of the new SMDs mentioned in this part.

Figure 2.15 Molecular structures of the new SM‐NFAs mentioned in this part....

Chapter 3

Figure 3.1 A brief survey of fullerenes. (a) C

60

and C

70

.. (b) The small...

Figure 3.2 Representative fullerene monoadduct acceptors.

Figure 3.3 Representative fullerene bisadduct acceptors.

Figure 3.4 Representative fullerene multiadduct acceptors.

Figure 3.5 Representative unconventional fullerene acceptors.

Chapter 4

Figure 4.1 Functionalization positions on a PDI.

Figure 4.2 Chemical structures of monomeric PDIs.

Figure 4.3 Chemical structures of selected PDI dimers.

Figure 4.4 (a) The synthetic route of NDP and SDP; single‐crystal structures...

Figure 4.5 Chemical structures of selected PDI trimers.

Figure 4.6 (a) X‐ray molecular structures of TPH

4b

and TPH‐Se

6a

(top view ...

Figure 4.7 Chemical structures of selected PDI tetramers.

Figure 4.8 Chemical structures of selected PDI tetramers.

Figure 4.9 Optimized geometry of (a) TTB‐PDI4 and (b) FTTB‐PDI4; (c) absorpt...

Figure 4.10 Chemical structures of non‐fullerene SMAs with different side ch...

Figure 4.11 Non‐fullerene small‐molecule acceptors with different end groups...

Figure 4.12 Chemical structures of IDTT‐based FREAs and its derivatives.

Figure 4.13 (a) Conformational locking of FREAs as demonstrated by ITC6‐IC. ...

Figure 4.14 (a) AFM images (1 μm × 1 μm, left: height images and right: phas...

Figure 4.15 Chemical structures of some representative FREAs with space unit...

Figure 4.16 (a) Transmittance spectra of PTB7‐Th:IEICS‐4F‐based single junct...

Figure 4.17 Chemical structures of asymmetric cored FREAs.

Figure 4.18 (a) GIWAXD patterns of TPT‐2F, TPTT‐2F, and TPTTT‐2F and their c...

Figure 4.19 (a) Theoretical simulation for optimal

N

‐alkyl chain conformatio...

Figure 4.20 Chemical structures of non‐fused acceptors.

Figure 4.21 (a) Possible rotamers and their energy–torsion angle (

E

–

θ

) ...

Figure 4.22 Chemical structures of BTA‐based A–DA′D–A‐type acceptors.

Figure 4.23 The single‐crystal structure of Y6.

Figure 4.24 Chemical structures of BT/Qx/Bse‐based A–DA′D–A‐type acceptors–....

Chapter 5

Figure 5.1 Chemical structures of typical copolymers based on pentacyclic an...

Figure 5.2 Chemical structures of some representative D–A copolymers based o...

Figure 5.3 Chemical structures of PTPTPTBT and PIDTCPDT‐DFBT.

Figure 5.4 Chemical structures of some representative NFAs based on heterope...

Figure 5.5 Chemical structures of NFAs based on heteroheptacenes with sp

3

‐br...

Figure 5.6 Chemical structures of NFAs based on heteroheptacenes without sp

3

Figure 5.7 Chemical structures of NFAs based on ladder‐type heteroacenes wit...

Figure 5.8 Chemical structures of some other NFAs.

Chapter 6

Figure 6.1 The key routes of PBDB‐T‐2Cl and PBDB‐TF polymers.

Figure 6.2 Theoretical calculation data, including twisting barriers of BDT‐...

Figure 6.3 X‐ray crystallographic structures of (a) IDIC‐4H, (b) IDIC4F, and...

Figure 6.4 Schematic diagram of

V

oc

in PSCs based on PTBCl

x

and PC

71

BM.

Chart 6.1 Polymer donor‐based chlorinated D unit backbone.

Chart 6.2 Polymer donor‐based chlorinated side chain of D unit.

Figure 6.5 Structure of monomer M1 (BDT‐T2Cl

s

) (a) and monomer M2 (BDT‐T4Cl)...

Figure 6.6 The scheme of chlorination and “Same‐A‐Strategy”.

Figure 6.7 Molecular structure and photovoltaic performance of PBDB‐T and PB...

Chart 6.3 Polymer donor‐based chlorinated backbone of A unit.

Figure 6.8 Synthesis routes of P(Th) and P(Cl).

Chart 6.4 Polymer donor‐based chlorinated π‐bridge.

Figure 6.9 Molecular structures of BTR and BTR‐Cl.

Chart 6.5 Small‐molecule acceptor‐based chlorinated IC end groups.

Figure 6.10 The molecule (a) and single‐crystal, (b) structure of BTIC‐BO‐4C...

Figure 6.11 (a) Molecule structure of BTIC‐2Cl‐γCF

3

, (b)

J–V

curves of...

Chapter 7

Figure 7.1 (a) Structure of single junction all‐polymer BHJ solar cells, (b)...

Figure 7.2 (a)

J

–

V

curve under illumination and (b) EQE versus wavelength fo...

Figure 7.3 Synthesis of NDI polymers.

Figure 7.4 Chemical structure of representative aromatic diimide‐based conju...

Figure 7.5 Three major strategies proposed to develop new BTI‐based building...

Figure 7.6 Synthetic route to (a) the fluorinated BTI monomers f‐FBTI2‐Br an...

Figure 7.7 Synthetic route to (a) the fluorinated monomers f‐FBTI2‐Br

via

a s...

Figure 7.8 (a) Chemical structures of imide‐functionalized arenes and hetero...

Figure 7.9 (a) Molecular structures of the polymer donor PTB7‐Th, the benchm...

Figure 7.10 (a) Molecular structure of the A–A type polymer acceptor L14 wit...

Figure 7.11 Principle of B←N unit.

Figure 7.12 (a) Chemical structures of the model compounds of BNTT, BNBP, an...

Figure 7.13 (a)

E

LUMO

alignments of eight polymers based on BNBP unit.; ...

Figure 7.14 (a) Chemical structures of P‐BNBP‐T, P‐BNBP‐DPP; (b) absorption ...

Figure 7.15 (a) Chemical structures of PBN‐10; (b) the AM 1.5G solar spectru...

Figure 7.16 (a) Chemical structures of P‐BN‐TPD and P‐BN‐IID; (b) optimized ...

Figure 7.17 (a) Chemical structures of P‐BNBP‐T and P‐BNBPP‐T; (b) grazing‐i...

Figure 7.18 (a) Chemical structures of P1 and PBN‐12; (b and c) 2D‐GIWAXS pa...

Figure 7.19 2D‐GIWAXS patterns (top) and AFM height images (down) of CD1:PBN...

Figure 7.20 Chemical structures of polymer acceptors bearing cyano groups....

Figure 7.21 Chemical structures of (a) IDIC‐C16 and (b) PZ1; (c) solution an...

Figure 7.22 Chemical structures of (a) TTPBT‐IC and (b) PJ1; UV–vis absorpti...

Figure 7.23 Spin‐coating process of all‐polymer BHJ blend and further therma...

Figure 7.24 Device structures of all reported all‐PSCs.

Figure 7.25 Stability enhancements in all‐PSCs under different situations....

Chapter 8

Figure 8.1 PCE against

V

oc

plots of the reported efficient organic solar cel...

Figure 8.2 Molecular structures of fullerene acceptors and the reported poly...

Figure 8.3 The representative molecular structures of PDI‐based NFAs.

Figure 8.4 The representative molecular structures of SMAs containing IC uni...

Figure 8.5 The representative molecular structures of BT‐based NFAs.

Figure 8.6 The representative molecular structures of BTA and Qx‐based NFAs....

Figure 8.7 The molecular structures of the polymers acceptors.

Chapter 9

Figure 9.1 Chemical structures of fullerene‐based “in‐chain” molecular dyads...

Figure 9.2 Chemical structures of multiple fullerene‐based “in‐chain” molecu...

Scheme 9.1 The synthetic route of fullerene‐based “in‐chain” molecular dyad

Figure 9.3 Chemical structures of fullerene‐based “side‐chain” D–A molecular...

Scheme 9.2 The synthetic route of fullerene‐based “in‐chain” triad

SM33

.

Figure 9.4 Chemical structures of PBI‐based molecular dyads.

Scheme 9.3 The synthetic route of PBI‐based molecular system

SM35–37

....

Figure 9.5 Chemical structures of block conjugated copolymers for SCOSCs (Pa...

Figure 9.6 Chemical structures of block conjugated copolymers for SCOSCs (Pa...

Scheme 9.4 The synthetic route of block copolymer

BCP12

. (i) Pd

2

(dba)

3

, P(

o

‐...

Scheme 9.5 Synthetic routes and chemical structures of

DCP1

and

DCP2

.

Scheme 9.6 Chemical structures and synthetic routes of

DCP3–DCP5

.

Scheme 9.7 Synthetic routes and chemical structures of

DCP6–10

.

Scheme 9.8 The chemical structures and synthetic routes of

DCP11–13

.

Figure 9.7 Chemical structures of the double‐cable polymers

DCP14

–

DCP23

.

Figure 9.8 Chemical structures of the double‐cable polymers

DCP24

–

DCP29

.

Figure 9.9 Chemical structures of the double‐cable polymers

DCP30

–

DCP34

.

Figure 9.10 Chemical structures of the double‐cable polymers

DCP35

–

DCP40

.

Figure 9.11 (a) AFM height and (b) phase images and (c) TEM images of the

SM

...

Figure 9.12 2D‐GIWAXS images of (a) BDTRh, (b) BDTRh:PCBM, and (c) BDTRh‐PCB...

Figure 9.13 TEM images and SAED patterns (inset) of

SM35

(a, d),

SM36

(b, e)...

Figure 9.14 (a–c) TEM images and (d–f) SAED patterns of

SM41

,

SM42

, and

SM43

Figure 9.15 AFM images (scale bar = 1 μm) of the active layer in PSC devices...

Figure 9.16 GIWAXS patterns of the as‐cast and annealed

BCP13

films. Out‐of‐...

Figure 9.17 (a–c) GIWAXS patterns of

DCP24–26

in thin films. (d)

J–V

...

Figure 9.18 (a) AFM phase images, (b) TEM images, (c) GIWAXS patterns, (d) G...

Figure 9.19 (a) GIMAXS profiles of thin films of

DCP35

with different anneal...

Figure 9.20 (a) AFM height images, (b) GIWAXS patterns, and (c) the related

Figure 9.21 (a) GIWAXS patterns, (b) the OOP and IP cut‐lines of the corresp...

Chapter 10

Figure 10.1 (a) Thermalization and transmission losses. (b) Arrangement of f...

Figure 10.2 Fullerene acceptors used in tandem OSCs.

Figure 10.3 Polymer donor materials used in tandem OSCs.

Figure 10.4 Small molecule donor materials used in tandem OSCs.

Figure 10.5 Small molecule acceptor materials used in tandem OSCs.

Figure 10.6 Predicted PCEs of 2T tandem solar cells based on semi‐empirical ...

Chapter 11

Figure 11.1 Polymer structures in thick‐film polymer‐fullerene binary device...

Figure 11.2 The chemical structures of polymers and non‐fullerene small‐mole...

Figure 11.3 Chemical structures of the polymers capable of demonstrating hig...

Figure 11.4 The chemical structures of polymers that perform well in all‐pol...

Figure 11.5 (a) Architecture of ITO‐free based OSCs and its TEM cross‐sectio...

Figure 11.6 (a) Device structure of all‐plastic OSCs, J − V characteristics ...

Figure 11.7 (a) Transfer‐printing technique, (b) transmittance spectra of tr...

Figure 11.8 (a) Comparison of square resistance and conductivity of the PEDO...

Figure 11.9 The AFM images of SWCNT film (a) before and (b) after PEDOT:PSS ...

Figure 11.10 (a) Schematic diagram of polymerization in carbon nanotube disp...

Figure 11.11 (a) Structures of substrate/MoO

x

/SWCNT/MoO

x

/PEDOT:PSS/PTB7:PC

71

Figure 11.12 (a) Diagram of flexible device structure and related energy lev...

Figure 11.13 (a) The optimal device structure, (b) energy level diagram, (c)...

Figure 11.14 (a) Diagram of PEDOT:PSS:RGO film by slot‐die coating, (b) stru...

Figure 11.15 (a) Diagram of OSCs and cross‐section SEM images with the struc...

Figure 11.16 (a) Diagram of fabricated Ag NWs with CIP method, and the SEM i...

Figure 11.17 (a) Flexible devices framework, (b) energy level diagram, (c)

J

...

Figure 11.18 (a) Energy level diagram, (b)

J–V

curves of flexible OSCs...

Figure 11.19 (a) Diagram of leaf internal structure, (b) fabrication route o...

Figure 11.20 Comparison between conventional spin coating process on glass a...

Figure 11.21 Schematic illustration of blade coating.

Figure 11.22 Schematic illustration of slot‐die coating.

Figure 11.23 Schematic illustration of the inkjet printing process.

Figure 11.24 Schematic illustration of the spray coating process.

Figure 11.25 (a) Schematic illustration of screen printing, (b) gravure prin...

Figure 11.26 R2R printing and coating machine for organic solar cells. (a) A...

Figure 11.27 Cross section and the equivalent circuit diagram of OSC modules...

Figure 11.28 Cross‐sectional diagram of module formed through single solar c...

Chapter 12

Figure 12.1 (a) The publication numbers of IoT and IPV from 2005–2020 in Web...

Figure 12.2 (a) The pictures of typical FL and LED light sources. Source: Yi...

Figure 12.3 (a) Schematic diagram and (b) sectional view of the indoor photo...

Figure 12.4 The molecular structures of (a) the donors, (b) fullerene accept...

Figure 12.5 (a) The device structure of a typical organic photovoltaic cell ...

Figure 12.6 (a)

J

–

V

curves of all‐polymer OPV under indoor lighting conditio...

Figure 12.7 (a) Absorption spectra of the donor and acceptors. (b) The

J

–

V

c...

Figure 12.8 (a)

J

–

V

, (b) FF, and (c) PCE curves of OPVs with three different...

Figure 12.9 (a) Absorbance spectral changes of PPDT2FBT:PC

71

BM with varying ...

Figure 12.10 (a) The

J–V

curves of eight pixels connected in series (r...

Chapter 13

Figure 13.1 Schematic energy band diagrams: (a) anode, donor, acceptor, and ...

Figure 13.2 (a) Scheme of demonstrating interfacial dipole generated by ioni...

Figure 13.3 (a) Typical conjugated zwitterions (polythiophene‐based zwitteri...

Figure 13.4 (a) Chemical structure and graphical charge distribution (DFT ca...

Scheme 13.1 Chemical structure of PEDOT: PSS.

Figure 13.5 The schematic self‐assembly process of PEDOT:PSS‐DA film after t...

Scheme 13.2 The chemical structure of some typical CPEs.

Scheme 13.3 The chemical structure of cross‐linkable hole transporting mater...

Scheme 13.4 Molecular structure of small‐molecule interlayer materials.

Scheme 13.5 Molecular structure of some typical fullerene interlayer materia...

Scheme 13.6 Molecular structure of some typical polymer cathode interlayer m...

Chapter 14

Figure 14.1 Overview of morphology characterization and manipulation methods...

Figure 14.2 (a) Schematic illustration of AFM. AFM (b) height and (c) phase ...

Figure 14.3 (a) TEM image of PTB7:PC

70

BM blend film cast from chlorobenzene ...

Figure 14.4 Schematic view of the typical (a) grazing incidence, (b) transmi...

Figure 14.5 Schematic illustration of typical 2D GIWAXS images demonstrating...

Figure 14.6 Schemes of the polymer: fullerene films with (a) strong and (b) ...

Figure 14.7 (a) A typical 2D GISAXS pattern of the BHJ active layer film. (b...

Figure 14.8 TOF‐GISANS patterns of P3HT:PC

60

BM film measured at different wa...

Figure 14.9 (a) Depth profile of PBDB‐T:ITIC film measured by XPS with etchi...

Figure 14.10 (a) The absorption spectra and (b) film‐depth‐dependent light a...

Figure 14.11 (a) Schematic illustration of thermal annealing. (b) 2D GIWAXS ...

Figure 14.12 Schematic illustration of (a) typical solvent vapor annealing p...

Figure 14.13 2D GIWAXS images of P3HT films cast from (a) CF and (b) DCB Sou...

Figure 14.14 TEM images of PTB7:PC

70

BM films cast from CB (a) without or (b)...

Figure 14.15 (a) Schematic images of the working mechanism of SA‐1 solid add...

Figure 14.16 XPS depth profiles of PBDB‐T:IT‐M films cast on (a) TiO

2

and (b...

Chapter 15

Figure 15.1 (a)

J–V

characteristics and (b) dark

J–V

characteris...

Figure 15.2 Typical photo‐CELIV transients measured for an OSC with a 20‐nm‐...

Figure 15.3 Double logarithmic plot of delay time‐dependent (a) carrier conc...

Figure 15.4 Double logarithmic plot of the photocurrent density as a functio...

Figure 15.5 Double logarithmic plot of

J

ph

–V

eff

characteristics obtain...

Figure 15.6 Transient photocurrents measured for samples consisting of a 400...

Figure 15.7 Transient photocurrents measured for samples with a reverse conf...

Figure 15.8 Schematic diagram illustrating the processes of exciton dissocia...

Figure 15.9 (a)

J

–

V

characteristics and (b) EQE spectra measured for the inv...

Figure 15.10 SEM images measured for ITO surfaces with (a) a pure ZnO EEL an...

Figure 15.11

J

ph

–

V

eff

characteristics of a set of structurally identical inv...

Figure 15.12 Double logarithmic plot of

J

ph

as a function of the intensity o...

Figure 15.13 (a) PDS spectra measured for the pure ZnO and Al‐modified ZnO l...

Figure 15.14 The high‐resolution XPS core level spectra (a) Al 2p and (b) C ...

Figure 15.15

J–V

characteristics of inverted OSCs with an Al‐modified ...

Figure 15.16 (a)

J

–

V

and (b) EQE characteristics measured for the PM6:IT‐4F‐...

Figure 15.17 (a) TEM and (b) high‐resolution TEM images measured for a solut...

Figure 15.18

η

CC

–

V

eff

characteristics of the NFA‐based OSCs with differ...

Figure 15.19 Transient photocurrents of the PM6:IT‐4F‐based OSCs with (a) a ...

Figure 15.20 Normalized

V

bi

– aging time characteristics measured for the NF...

Figure 15.21 (a) PCE, (b)

V

oc

, (c)

J

sc

, and (d) FF measured for the NFA‐base...

Figure 15.22 Normalized

η

CC

as a function of the aging time, measured f...

Figure 15.23 Absorption spectra measured for the (a) MoO

3

/antimonene/PM6 lay...

Chapter 16

Figure 16.1 Blackbody radiation spectrum at

T

 = 300 K, absorption spectrum o...

Figure 16.2 (a)

V

oc,sq

and (b) Δ

V

r

as a function of

E

g

for an ideal solar ce...

Figure 16.3 Definition of different voltage losses in a real‐world solar cel...

Figure 16.4 (a) A schematic picture for the device architecture of an organi...

Figure 16.5 (a) Electroluminescence spectra of an organic solar cell based o...

Figure 16.6 A three‐state model illustrating the competition between CT stat...

Figure 16.7 Potential energy diagram for the excited CT state and the ground...

Figure 16.8 (a) Determination of CT state‐related parameters for an organic ...

Figure 16.9 Definition of

E

g

for organic semiconductors. (a) A schematic pic...

Figure 16.10 A schematic picture of a three‐state model used to show the imp...

Chapter 17

Figure 17.1 (a) Photo‐induced dimerization measured with UV–vis absorption i...

Figure 17.2 (a) Normalized photovoltaic performance based on different accep...

Figure 17.3 (a) Normalized photovoltaic performance in ternary devices with ...

Figure 17.4 (a) Chemical structure of P3HT‐b‐P3TODT and bis‐PCBA, which affo...

Figure 17.5 (a) PCE of solar cells with OPV‐C

70

dyad film annealed at 110 °C...

Figure 17.6 Stability enhancement using crosslinking. (a) Bromine‐functional...

Figure 17.7 Stability of (a) P3HT:PC

61

BM and (b) PTB7‐Th:PC

61

BM cells with d...

Figure 17.8 (a and b) The third component 5TRh‐PCBM in PTB7‐Th:PC

71

BM (aged ...

Figure 17.9 (a) Stability of bilayer and BHJ devices based on PffBT4T‐2OD wi...

Figure 17.10 Reported organic solar cells with excellent stability. (a) Norm...

Figure 17.11 (a) Schematic of the device structure. (b)

External quantum eff

...

Chapter 18

Figure 18.1 The potential application scenarios of OSCs.

Figure 18.2 Building‐integrated photovoltaics with semitransparent OSC modul...

Figure 18.3 The solar panels were installed in a solar park. (a) The entire ...

Figure 18.4 A color and transparency‐switchable ST‐OSC. (a) Illustration of ...

Figure 18.5 (a) Images of a commercial module fabricated by

BELECTRIC OSC

. (...

Figure 18.6 Schematic of the energy fluxes for OSC‐greenhouse with shades de...

Figure 18.7 (a) Device structure of the flexible opaque OSCs. (b) An install...

Figure 18.8 (a) Schematic summary of the process used to fabricate wearable ...

Figure 18.9 (a) Schematic of a double‐grating‐patterned OSC integrated with ...

Figure 18.10 (A) The schematic device structure of near‐IR photoresponsive u...

Figure 18.11 Textile‐based washable OSCs. (a) Photograph of the washing proc...

Figure 18.12 The 1D structured OSCs textiles. (a) Fabrication of the coaxial...

Figure 18.13 Schematic illustration of a photovoltaics‐integrated energy sto...

Figure 18.14 The schematic and working mechanism of the OSC‐integrated photo...

Figure 18.15 Fiber‐based photocharging batteries. (a) A photograph of a wear...

Figure 18.16 (a) Schematic representation for OSC‐biased water splitting usi...

Figure 18.17 (a) Illustration of the solar glasses assembly with the organic...

Guide

Cover

Table of Contents

Title Page

Copyright

Preface

Begin Reading

Index

Wiley End User License Agreement

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Organic Solar Cells

Materials Design, Technology and Commercialization

Edited by Liming Ding

Editor

Prof. Liming DingNational Center for Nanoscience and TechnologyNo.11 ZhongGuanCunBeiYiTiao100190 BeijingChina

Cover Image: © Outflow_Designs/Shutterstock

All books published by WILEY‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

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© 2022 WILEY‐VCH GmbH, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978‐3‐527‐34933‐3ePDF ISBN: 978‐3‐527‐83364‐1ePub ISBN: 978‐3‐527‐83366‐5oBook ISBN: 978‐3‐527‐83365‐8

Preface

This is a fabulous time for me to write two prefaces for my first two books in my life! Time goes really fast. I think a lot about the old days, the choices, and interesting experiences. When I finished three years in Chemistry Department of Anhui University, I needed to choose my major, and there were three majors: chemical analysis, organic synthesis, and polymer science. I chose polymer, because I thought polymer would be more fantastic and useful; that was 1987. The last semester I chose lecturer Wei Yang (now emeritus professor in SCUT) as my thesis supervisor to do copolymerization aiming to obtain materials with good mechanical properties. The time with supervisor Wei Yang built my preliminary experience on chemicals, reaction, and polymerization. During 1990–1998, I did my MS, PhD, postdoc work on solid polymer electrolytes and electron transfer dynamics, in Changchun Institute of Applied Chemistry (CIAC), which was the biggest institute in Chinese Academy of Sciences. For my PhD period, I was a joint student in CIAC. My supervisors, Professors Zinan Zhou, Yunqing Lin (CIAC), Dezhu Ma, Chengzong Yang (USTC), Shaojun Dong, and Erkang Wang (CIAC), stimulated my spirit and kindly helped me, and these will stay in my memory forever. During my postdoc time, I really got interested in optoelectronic devices based on conjugated polymers. In October of 1997, Professor Olle Inganäs interviewed me in a hotel in Wangfujing, Beijing; we talked around 25 min, then Olle kindly invited me to a small restaurant nearby for lunch. Before Christmas I received the postdoc offer from Olle. Without any experimental background on devices, I did learn a lot from those old group members in Linköping University on how to cut ITO glass, etching, spin coating, vacuum evaporation, measurements, etc. All new to me. I quickly learned how to fabricate polymer solar cells and polymer light‐emitting diodes. That time, I made solar cells with a trilayer structure (Synthetic Metals 2000, 110, 133–140). Sweden, a small kindom, stays really special, and a very beautiful land, people like Olle doing cool stuff there everyday, serious, quiet, and outstanding! Later, I moved to the United States and worked with Robert Haddon on CNTs, Frank Karasz on PLEDs and organic solar cells (OSCs), Mike Durstock and Liming Dai on OSCs, and Tom Russell on photoactive polymers, block copolymers and phase separation. I worked in Konarka Lowell as a senior scientist for one year on flexible polymer solar cells, doing blade coating, materials screening, and device optimization. It was cool to learn the structure, running and commercial operation of a facing‐future high‐tech company. In 2010, I came back to China and joined National Center for Nanoscience and Technology as a full professor. My research project was on OSCs. We have invented many building blocks and high‐performance materials such as copolymer donors, non‐fullerene small molecular acceptors, and fullerene acceptors. We have pushed the PCE record for OSCs from 14% to 18%. This jumping just took two years, really awesome! We hold the dream that one day single‐junction OSCs will deliver PCEs over 20%. I think it is the right time to deliver a book on OSCs, a way to sum up the past and to face the future, to challenge the PCE limit and those commercialization issues. All the contributing authors have done excellent jobs in their respective direction. The topic goes from polymer donors, p‐type materials, fullerene acceptors, non‐fullerene small molecular acceptors, ladder‐type heteroacenes, chlorination, all‐polymer solar cells, single component, tandem structure, large‐area fabrication, indoor application, interfacial design, morphology control, stability, to voltage loss, covering almost all research hotspots. This book would help those people who have interests in OSCs or who are working in the same field, no matter students or colleagues, academic or industry. Special thanks to Dr. Shaoyu Qian, without her trust and invitation, this won't happen! I would thank Kat Wong and Farhath Fathima for their nice assistance and patience. I appreciate the help from my team members: Ling Liu, Ke Jin, Xiaoyan Du, Zuo Xiao, Chuantian Zuo, Jiamin Cao and Shan Chen.

At last, I thank my mom for her eternal love.

Beijing, 28 September 2021

Liming Ding

1Conjugated Polymer Donors for Organic Solar Cells

Xiaopeng Xu1, Xiyue Yuan2, Qunping Fan3, Chunhui Duan2, Maojie Zhang3, and Qiang Peng1

1Sichuan University, School of Chemical Engineering, State Key Laboratory of Polymer Materials Engineering, No. 24 South Section 1, Yihuan Road, Chengdu, 610065, P.R. China

2South China University of Technology, Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, 381 Wushan Road, Tianhe District, Guangzhou, 510640, P.R. China

3Soochow University, Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, 199 Ren'ai Road, Suzhou, 215123, P.R. China

1.1 Introduction

Organic solar cells (OSCs) are the devices that can directly convert solar energy into electricity with the advantages of low cost, light weight, and the potential for roll‐to‐roll fabrication on flexible substrates, which make them promising candidates for inexpensive renewable power sources [1–3]. At present, the highest power conversion efficiency (PCE) of OSCs in laboratory has exceeded 18% [4]. Important progresses have been also made in scalability and device stability, which demonstrated the great application prospect of this technology [5,6]. These progresses were greatly benefitted from the design and synthesis of donor polymers with wide spectral absorption coverage to the solar spectrum and matched energy levels. Based on the optical bandgaps (s), donor polymers employed in OSCs can be divided into three major types: low bandgap (LBG) polymers (Eg < 1.6 eV), medium bandgap (MBG) polymers (1.6 eV < Eg < 1.8 eV), and wide bandgap (WBG) polymers (Eg &gt; 1.8 eV) (Figure 1.1a) [7]. In the early stage of OSCs field, fullerene derivatives were the dominant acceptors, which are poor light absorbers. As a result, the donor polymers are responsible for light harvesting in the resulting OSCs. Correspondingly, the LBG polymers played a more important role than the MBG and WBG polymers at that stage [8]. Nevertheless, LBG polymers with reduced generally had a high‐lying highest occupied molecular orbital (HOMO) energy level, which resulted in a limited open‐circuit voltage (Voc) in the corresponding OSCs [9]. MBG polymers could have more potential to deepen the HOMO level without significantly increasing the bandgap, which afforded higher Voc without sacrificing short‐current density (Jsc) in the resulted OSCs [9,10]. Although the Jscs of OSCs based on WBG polymers were limited by their narrow absorptions, they were also key components to complement the absorption spectra with LBG counterparts and achieve high Voc in the multi‐junction, ternary blend, or the currently prevailing non‐fullerene OSCs [8–11].

Figure 1.1 (a) UV–vis–near‐infrared (NIR) absorption of different bandgap polymers. (b) Principle of bandgap lowering by donor–acceptor interaction. (c) LBG polymers constructed by using “strong donor‐strong acceptor” configuration. (d) MBG polymers constructed by using “weak donor‐strong acceptor” configuration. (e) WBG polymers constructed by using “weak donor‐weak acceptor” configuration.

Source: Xiaopeng Xu.

Constructing donor–acceptor (D–A)‐type copolymers has been demonstrated to be the most successful strategy to develop high‐performance donor polymers (Figure 1.1b). With rational choice of electron‐donating and electron‐withdrawing units, the absorption ranges and frontier energy levels can be readily tuned. The “push‐pull” effect between D and A units has distinct effect on the bandgaps of the resulted polymers: (i) the combination of “strong donor” and “strong acceptor” could be a feasible way to achieve a LBG polymer (Figure 1.1c); (ii) the pair of “weak donor” and “strong acceptor” could be employed to construct a MBG polymer (Figure 1.1d); and (iii) the utilization of “weak donor” and “weak acceptor” could be effective to build a WBG polymer (Figure 1.1e). Compared to the LBG polymer, the weak electron‐donating ability of donor motif delivers a low‐lying HOMO energy level of the MBG and WBG polymers, which is beneficial to realize high Voc in the resulting polymer solar cells (PSCs) [10,11]. Compared to the WBG polymer, the strong electron‐withdrawing ability of acceptor block lowers the lowest unoccupied molecular orbital (LUMO) energy level of the MBG polymer, which enables a reduced bandgap viaintramolecular charge transfer (ICT) [12]. In the following part, we will introduce the design strategies of LBG, MBG, and WBG polymers and analyze their photovoltaic properties.

1.2 LBG Polymers

LBG‐conjugated polymers are usually obtained via the design strategies as follows [13,14]. First, stabilization of the quinoidal resonance structure in conjugated polymers. Generally, two kinds of resonance structures, i.e. aromatic and quinoidal form coexist in conjugated polymers. As compared to the aromatic form, the quinoidal form has a smaller bandgap but is energetically less stable due to the destruction of the original aromaticity. Second, copolymerization of D unit and A unit alternatively to afford the so‐called D–A copolymers [15]. Reduced optical gaps (Eg3 in Figure 1.1b) in an alternating copolymer can be achieved due to the molecular orbital hybrid of the electron‐rich (D) and electron‐deficient (A) moiety. Besides, the HOMO level of the polymers is mainly influenced by the donor units, while the LUMO level is determined by the acceptor units. Donor units employed in high‐performance LBG polymers are mostly thiophene ring‐containing building blocks with strong electron‐donating capability. Compared to donor units, acceptor units play a more important role in constructing LBG polymers because the absorption spectra, energy levels, and aggregation properties can be more easily tuned by selecting appropriate acceptor units [16]. The common acceptor units with stronger electron‐accepting ability include 2,1,3‐benzothiadiazole (BT), isoindigo (IID), and diketopyrrolopyrrole (DPP). In this section, we will introduce the design strategies of LBG polymers at first. After that, several representative types of LBG polymers and their photovoltaic properties will be analyzed.

1.2.1 LBG Polymers Based on Benzothiadiazole (BT)

2,1,3‐Benzothiadiazole (BT) is a widely used acceptor unit for constructing LBG polymers in a D–A‐type framework (Figure 1.2). One of the representative LBG polymers is P1 [17,18], a copolymer‐based on cyclopentadithiophene (CPDT) and BT with an Eg of 1.47 eV. By replacing the carbon atom with silicon atom on CPDT, the polymer P2 [19,20] with a higher crystallinity and improved charge transport properties was generated, which afforded a certified PCE of 5.2% when blended with a fullerene derivative in OSCs. When introducing P2 as the third component into the PTB7:PC71BM blend host, a higher fill factor (FF) of 77% was obtained due to the reduction of recombination losses. Correspondingly, a PCE improvement from 7.52% to 8.60% was achieved [21]. Replacing S with O in heteroaromatic rings tends to offer a more positive oxidation potential, which is beneficial for obtaining a higher Voc in OSCs [18]. This was reflected by P3, which exhibited much deeper‐lying HOMO level and higher Voc than P1 in OSCs. However, this polymer could not generate photocurrent, which was possibly caused by the reduced driving force for exciton dissociation.

Figure 1.2 The chemical structures of BT and its derived building blocks.

Source: Xiyue Yuan.

Fluorination is effective to improve the photovoltaic properties of conjugated polymers via tuning the frontier orbital energy levels and improving molecular ordering. However, fluorination can also bring negative effects on resulting polymers, such as poor solubility and excessive aggregation in organic solvents. Hence, the degree of fluorination shall be optimized to achieve a high‐efficiency OSCs. Neher and coworkers [22] showed that the polymer with mono‐fluorination on BT (P4) exhibited better photovoltaic performance than the polymers with non‐ and di‐fluorination on BT (P1, P5) due to the stronger tendency to take face‐on orientation when blended with PC71BM. Similar fluorination effects were also observed by Jo et al. on the polymers P6–P8 [23]. Yang et al. [24] inserted a strong electron‐donating oxygen atom into the CPDT unit to form the dithienopyran (DTP) unit for lowering Eg. The resulting polymer P9 exhibited a narrow Eg of 1.38 eV, and a deep HOMO level of −5.26 eV. Single‐junction OSCs based on P9:PC71BM blend showed over 60% external quantum efficiency (EQEs) and effective optical response up to 900 nm. Moreover, a certified PCE of 10.6% in tandem OSCs based on this polymer was achieved. Guo and coworkers [25] reported a BT‐based polymer P10 with an Eg of 1.46 eV by using a head‐to‐head substituted bithiophenes as the donor units, which afforded a promising PCE of 9.8% in fullerene‐based OSCs. Replacing the phenyl ring on BT unit with pyridine ring leads to a new building block, thiadiazolo[3,4‐c]pyridine (PyT), which possesses higher electron affinity and affords narrower bandgap in conjugated polymers. You and coworkers [26] reported a LBG polymer P11 based on PyT, which exhibited an Eg of 1.51 eV and a PCE of 6.3% in OSCs. When utilizing 4,4‐bis(2‐ethylhexyl)‐4H‐germolo[3,2‐b:4,5‐b′]dithiophene (DTG) as the electron‐rich unit, the polymer P12 based on PyT exhibited a very low Eg of 1.32 eV and a decent PCE of 6.6% in inverted OSCs [27]. The chemical structures of P1–P12 are showed in Figure 1.3, and the corresponding photovoltaic parameters of OSCs are summarized in Table 1.1.

Figure 1.3 Chemical structures of the BT‐derived conjugated polymers P1–P12.

Source: Xiyue Yuan.

Table 1.1 Optoelectronic properties and device performances of P1–P12.

Polymer

(eV)

HOMO/LUMO (eV)

Acceptor

V

oc

(V)

J

sc

(mA cm

−2

)

FF

PCE (%)

References

P1

1.47

−5.30/−3.55

PC

61

BM

0.65

11.0

0.47

3.2

[17]

P2

1.45

−5.05/−3.27

PC

61

BM

0.58

14.9

0.61

5.2

[20]

P3

a)

1.47

−5.39/−3.71

PC

61

BM

0.78

5.2

0.60

2.5

[18]

P4

1.45

−5.35/−3.90

PC

71

BM

0.74

14.1

0.58

5.9

[22]

P5

1.51

−5.34/−3.52

PC

71

BM

0.85

12.6

0.52

5.6

[24]

P6

1.57

−5.33/−3.76

PC

71

BM

0.80

14.1

0.63

7.1

[23]

P7

1.57

−5.37/−3.80

PC

71

BM

0.82

15.7

0.71

9.1

[23]

P8

1.59

−5.46/−3.87

PC

71

BM

0.82

13.3

0.59

6.4

[23]

P9

1.38

−5.26/−3.61

PC

71

BM

0.68

17.8

0.65

7.9

[24]

P10

1.46

−5.20/−3.74

PC

71

BM

0.66

20.7

0.71

9.8

[25]

P11

1.51

−5.47/−3.64

PC

61

BM

0.85

12.8

0.58

6.3

[26]

P12

1.32

−4.90/−3.60

PC

71

BM

0.59

19.6

0.57

6.6

[27]

a) For P3, energy levels are determined from cyclic voltammetry .

Source: Based on Hendriks et al. [28].

Fusing two BT units leads to the formation of naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NT), which possesses a larger planar structure and higher electron affinity than BT unit (Figure 1.4). The pioneering work based on NT was done by Cao and coworkers along with the creation of P13, which exhibited an Eg of 1.58 eV and a PCE of 6.0% when blended with PC71BM [29]. After that, more narrow bandgap polymers based on NT were developed for application in OSCs. For example, the polymer P14 bearing quaterthiophene donor units and NT acceptor units exhibited a high PCE of 10.1% in OSCs with an inverted structure at the active layer thickness of 290 nm due to the high crystallinity and hole mobility of the polymer [30]. More remarkably, high‐performance thick‐film OSCs were achieved by more NT‐based polymers (P16–P20), which suggested the prospect of NT‐based polymers in large‐scale manufacturing of OSCs [31–33]. To reduce the energy loss (Eloss) of NT polymer‐based OSCs, Takimiya and coworkers created a new building block naphtho[1,2‐c:5,6‐c′]bis[1,2,5]oxadiazole (NOz) by replacing the sulfur atom on NT unit with oxygen atom. The resulting polymer P15 exhibited similar Eg as P14 but significantly enhanced Voc and greatly reduced Eloss in OSCs when blended with the same electron acceptor (≈0.85 versus ≈0.55 eV) [34]. The chemical structures of P13–P20 are showed in Figure 1.4, and the corresponding photovoltaic parameters of OSCs are summarized in Table 1.2.

Figure 1.4 Chemical structures of the NT‐derived conjugated polymers P13–P20.

Source: Xiyue Yuan.

Table 1.2 Optoelectronic properties and device performances of P13–P20.

Polymer

(eV)

HOMO/LUMO (eV)

Acceptor

V

oc

(V)

J

sc

(mA cm

−2

)

FF (%)

PCE (%)

References

P13

1.58

−5.19/−3.26

PC

71

BM

0.80

11.7

0.61

6.0

[29]

P14

1.54

−5.16/−3.77

PC

71

BM

0.71

19.4

0.73

10.1

[30]

P15

1.52

−5.48/−3.65

PC

71

BM

0.96

14.5

0.64

8.9

[34]

P16

1.56

−5.14/−3.46

PC

61

BM

0.71

19.4

0.73

10.1

[33]

P17

1.60

−5.38/−3.53

PC

71

BM

0.82

19.3

0.67

10.5

[33]

P18

1.42

−5.36/−3.48

PC

71

BM

0.77

20.2

0.72

11.3

[32]

P19

1.52

−5.42/−3.48

PC

71

BM

0.84

16.5

0.72

10.0

[32]

P20

1.40

−5.29/−3.40

PC

71

BM

0.72

19.1

0.73

10.3

[31]

[1,2,5]Thiadiazolo[3,4‐f]isoindole‐5,7‐dione (TID) is another strong acceptor unit derived from BT (Figure 1.5). McCulloch and coworkers [35] reported a LBG polymer P21 based on this acceptor unit, which exhibited ideal frontier orbital energy levels for OSCs. This polymer can be solution‐processed in a blend with PC71BM from a single solvent to reproducibly afford OSCs with the best PCE reaching 8.3%. Wang et al. [36] reported P22 with a low Eg of 1.49 eV, which was copolymerized from TID and the electron‐rich unit indacenodithieno[3,2‐b]thiophene (IDTT). The OSCs based on P22:PC71BM attained a good PCE of 6.7% with a high Voc of 1.0 V, leading to the Eloss as low as 0.49 eV. In addition to TID, Facchetti and coworkers [37] reported a new electron‐accepting building block benzo[1,2‐d:4,5‐d′]bis([1,2,3]thiadiazole) (iso‐BBT). The resulting polymer P23 exhibited an Eg of 1.40 eV and afforded a PCE of 10.3% when blended with PC61BM. Li and coworkers [38] introduced quinoidal structure design concept into the BT‐derived unit and obtained the polymer P24 with an Eg of 1.45 eV. When employed in fullerene‐based OSCs, P24 showed a PCE of 6.1%. The chemical structures of P21–P24 are showed in Figure 1.5, and the corresponding photovoltaic parameters of OSCs are summarized in Table 1.3.

Figure 1.5 Chemical structures of the BT‐derived conjugated polymers P21–P24.

Source: Xiyue Yuan.

Table 1.3 Optoelectronic properties and device performances of P21–P24.

Polymer

(eV)

HOMO/LUMO (eV)

Acceptor

V

oc

(V)

J

sc

(mA cm

−2

)

FF

PCE (%)

References

P21

a)

1.50

−5.20/−3.70

PC

71

BM

0.80

16.5

0.63

8.3

[35]

P22

1.49

−5.89/−3.84

PC

71

BM

1.00

12.6

0.53

6.7

[36]

P23

1.40

−5.43/−4.03

PC

61