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- Herausgeber: Wiley-VCH
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- Sprache: Englisch
An introduction to a key tool in the cultivation of sustainable energy sources
Composite materials combine two or more materials with distinct chemical properties. These composites can improve on design flexibility, specialization of properties, chemical resistance, and other advantages relative to traditional materials. Perovskite solar cells based on composite materials might therefore acquire the capacity to solve a range of critical issues.
Composites-Based Perovskite Solar Cells offers an overview of these cells, their properties, and their applications. Beginning with an introduction to the fundamental principles of perovskite solar cell construction, the book surveys different configurations, stability issues, and much more. The result is a one-stop shop for anyone looking to understand these potentially critical tools in the fight for a sustainable energy grid.
Readers will also find:
- Methods for fabricating perovskite-based solar cells
- Detailed discussion of Pb-perovskites and Pb-free perovskites, composites-based materials in tandem solar cells, and many more
- A unique perspective from which to revisit approaches developed in the community of materials scientists
Composites-Based Perovskite Solar Cells is ideal for surface physicists and chemists, solid state physicists and chemists, electrical engineers, and materials scientists of all kinds.
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 429
Veröffentlichungsjahr: 2025
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Preface
1 Introduction – Why Composites‐Based Perovskite Solar Cells?
1.1 Need to Develop Composites‐Based Perovskite Solar Cells
1.2 Fabrication Strategy for Composites‐Based Perovskite Solar Cells
References
2 Hybrid Perovskites and Solar Cells
2.1 Perovskite Materials
2.2 Perovskite Solar Cells
2.3 Limitations and Improvements of Energy Conversion in Perovskite Solar Cells
References
3 Fundamentals and Benefits of Functional Composite Materials
3.1 Introduction to Composite Functional Materials
3.2 Development of Composites‐Based Perovskite Solar Cells
References
4 Stability and Efficiency Loss Issues of Perovskite‐Based Devices
4.1 Materials Instability
4.2 Device Heterointerface Instability
4.3 Solutions for Instability Problems
References
5 Composites‐Based Charge‐Transport and Interfacial Materials
5.1 Organic‐Based Composites
5.2 Inorganic‐Based Composites with Metal and Metal Oxide
5.3 Carbon‐Based Composites
References
6 Composite‐Based Pb‐Perovskite Materials as Absorbers
6.1 Organic Additives‐Based Perovskite Composites
6.2 Inorganic Additives‐Based Perovskite Composites
6.3 Low‐Dimensional (LD)/Three‐Dimensional (3D) Heterostructure Perovskite Composites
6.4 Quantum Dot (QD) Additives‐Based Perovskite Composites
6.5 Reduced Film Strain by Composites‐Based Perovskites
References
7 Composites‐Based Pb‐Free Perovskite Materials as Absorbers
7.1 Inorganic Additives‐Based Perovskite Composites
7.2 Organic Additives‐Based Perovskite Composites
7.3 Carbon Additives‐Based Perovskite Composites
References
8 Composite‐Based Perovskite Materials in Tandem Solar Cells
8.1 Introduction
8.2 Configuration of Perovskite‐Based Tandems
8.3 Perovskite Alloy‐Based Composites as Absorbers
8.4 Additives‐Based Perovskite Composites as Absorbers
8.5 Composite‐Based Interconnection Layers (ICLs)
8.6 Composite‐Based Charge Transport Layers
8.7 Composite‐Based Interfacial Layers in Tandems
References
9 Issues for Commercialization of Perovskite Solar Cells
9.1 Introduction to The Current Status of Perovskite Solar Cells
9.2 Solutions to Stability Issues
9.3 Upscaling, Commercialization, and Challenges
9.4 Status of Solar Modules Production
References
10 Characterization Methods for Composite‐Based Perovskite Solar Cells
10.1 Composite‐Based Perovskite Films Characterization
10.2 Devices Characterization
References
11 Perspectives and Future Work of Composites‐Based Perovskite Solar Cells
11.1 Perspectives of Composites‐Based Perovskite Solar Cells
11.2 Future Work for Composites‐Based Perovskite Solar Cells
References
Index
End User License Agreement
List of Tables
Chapter 3
Table 3.1 Classification of composites.
Table 3.2 Properties of composites depending on matrix and reinforced mater...
Chapter 5
Table 5.1 Power conversion efficiencies of perovskite solar cells with diff...
Table 5.2 Power conversion efficiencies of perovskite solar cells with diff...
Chapter 7
Table 7.1 Efficiency and stability of Sn‐PSCs with different structures and...
Table 7.2 Efficiency and stability of Sn‐PSCs with lead content ≤50% with d...
Table 7.3 Efficiency and stability of Sn‐based PSCs with different Lewis ba...
Table 7.4 Effect of PTN‐Br on hole and electron mobilities, evaluated throu...
Table 7.5 Photovoltaic parameters of Sn‐PS solar cells with and without N
0.
...
Chapter 9
Table 9.1 Summary of tests of the IEC 61215 for perovskite solar modules....
List of Illustrations
Chapter 1
Figure 1.1 Schematic illustration of the development strategy of composites‐...
Figure 1.2 Schematic illustration of an efficient strategy for the fabricati...
Chapter 2
Figure 2.1 (a) Typical 3D hybrid perovskite structure ABX
3
(A = organic cati...
Figure 2.2 Shockley–Queisser efficiency limit, and
V
oc
and
J
sc
.
Figure 2.3 Band gaps of 2D (
n
= 1) and quasi‐2D BA
2
MA
n
−1
Pb
n
I
3
n
+1
(...
Figure 2.4 The 2D structure of Ruddlesden–Popper (RP) (top) and Dion–Jacobso...
Figure 2.5 The structure of 0D and 1D perovskites.
Figure 2.6 The S–Q theoretical limit for the PCE and
J
sc
of single‐junction ...
Figure 2.7 (a) The nucleation and growth processes of perovskite films. (b) ...
Figure 2.8 Perovskite solar cell working mechanism: charge generation, charg...
Figure 2.9 Typical configurations of perovskite solar cell reported.
Figure 2.10 (a) Photographs of perovskite films and corresponding FE‐SEM top...
Figure 2.11 (a) XRD patterns with FWHM values at peaks 14.1° and 28.4° (inse...
Figure 2.12 Interface defects in PSCs.
Chapter 3
Figure 3.1 Advantages of functional composite materials in the active, elect...
Figure 3.2 (a) Perovskite ABX
3
tetragonal crystal structure, with (b) common...
Chapter 4
Figure 4.1 Schematic representation of typical MAPbI
3
degradation processes ...
Figure 4.2 (a) PL spectra of Cs
0.05
FA
0.70
MA
0.25
PbI
2.25
Br
0.75
perovskite film...
Figure 4.3 Perovskite crystal lattice: (a) perfect lattice, (b) A‐site vacan...
Figure 4.4 Schematic representations of the FAPbI
3
surface termination types...
Figure 4.5 (a) Schematic of the lift‐off process of perovskite film and (b) ...
Figure 4.6 Strain behavior in a perovskite thin film and corresponding XRD p...
Figure 4.7 (a,b) GIXRD spectra at different tilt angles, (c) linear fit of r...
Figure 4.8 Migration path for the (a)
V
I
, (b)
V
MA
, and (c)
V
Pb
vacancy defec...
Figure 4.9 HAADF‐STEM and SAD images for in situ electrical biasing transmis...
Figure 4.10 Schematic illustration of NiO
x
structural defects and the issues...
Figure 4.11 Schematic illustration of a mechanism of AgI formation by extern...
Figure 4.12 Formation energies (
Δ
H
) of interstitial metal impurities in...
Figure 4.13 (a) Schematic illustration of the diffusion path of an interstit...
Figure 4.14 Schematic of an electrical model for contact equilibration in PS...
Figure 4.15 Schematic illustration of device configuration based on perovski...
Figure 4.16 Schematic illustration of device encapsulation: (a,b) gap encaps...
Chapter 5
Figure 5.1
(
a) Schematic of planar n‐i‐p perovskite solar cells with CPTA as ...
Figure 5.2 Device parameters of fresh cells and those aged under the thermal...
Figure 5.3 (a) Configuration diagram of PSCs; energy‐level alignment diagram...
Figure 5.4
(
a) Cross‐section SEM images of perovskite SC device. (b) PCE of P...
Figure 5.5 (a) Configuration structure of PSCs, and corresponding device per...
Chapter 6
Figure 6.1 Schematic of the distribution of multications and growth process ...
Figure 6.2 (a) The cross‐linking illustration of two neighboring structures ...
Figure 6.3 (a,b) SEM images for surface morphology, (c) FWHM values, (d) PL ...
Figure 6.4 (a–d) XPS spectra of I 3d, Pb 4f, N 1s, and C 1s for 3D perovskit...
Figure 6.5 Illustration of the fabrication processes of the passivated perov...
Figure 6.6 (a,b) Cross‐view SEM images of the pristine and passivated perovs...
Figure 6.7 (a)
J–V
curves and (b,c) average
V
oc
and FF for pristine an...
Figure 6.8 Schematic illustration (left) of band diagram (right) of a hole‐c...
Figure 6.9 Conceptual illustration and performance of mesoscopic semitranspa...
Figure 6.10 (a) Schematic illustration of the energy band diagram and blocki...
Figure 6.11 (a) XPS spectra of iodide on a gold electrode in (a) perovskite,...
Figure 6.12 (a) Cross‐sectional SEM image of the cell of FTO/STO/mp‐AG/MAPbI
Figure 6.13 (a) Energy diagram of the champion device NiO‐rGO structure. (b)...
Figure 6.14 (a) SEM and AFM images of (a) triple‐cation CsFAMA‐perovskite an...
Figure 6.15 (a) X‐ray crystal structure of KPb
2
Br
5
, (b) dynamic light scatte...
Figure 6.16 XRD patterns of films deposited from a precursor solution aged f...
Figure 6.17 The FIB‐cut cross‐sectional HRTEM image for (a) 2D
–
3D pero...
Figure 6.18 (a) Current density
–
voltage (
J–V
) curves of control ...
Figure 6.19 (a) The configuration with a cross‐sectional view of a solar mod...
Figure 6.20 (a) Formation processes of 3D/1D or 3D/0D heterostructures, (b–d...
Figure 6.21 (a) Schematic illustration of CsPbBrCl
2
PQDs well‐distributed on...
Figure 6.22 (a) Thermal stability of CsM‐0.1 CNP composite film by UV
–
Figure 6.23 (a) Raman peaks of CsPbBr
3
perovskite and Ti
3
C
2
Cl
x
MXene‐based C...
Figure 6.24 (a) Schematic illustration of lattice strain regulation via a π‐...
Figure 6.25 (a–c) GIXRD spectra at different tilt angles for 2θ at 31.58° an...
Chapter 7
Figure 7.1 (a) A schematic diagram of FASnI
3
perovskite solar cell, highligh...
Figure 7.2 Ascorbic acid was introduced for the first time as an effective a...
Figure 7.3
(
a) Depiction outlining the interaction between PMMA and FASnI
3
at...
Figure 7.4 (a)
J‐V
characteristics (inset, the device configuration of...
Figure 7.5 (a,b) FESEM images of Sn‐PS and Sn‐PS:N
0.12
GO films with size dis...
Figure 7.6
(
a) Current density–voltage plots and (b) EQE spectra and integrat...
Figure 7.7 Comparison of (a) long‐term stability of Sn‐PSCs without encapsul...
Chapter 8
Figure 8.1 Theoretical efficiency limit for 2T and 4T tandems with different...
Figure 8.2 Schematic diagrams of 4T and 2T TSCs.
Figure 8.3 Schematic of widely used perovskite/silicon tandem structures: (a...
Figure 8.4 Schematic of all perovskite tandem solar cells.
Figure 8.5 Schematic of (a) perovskite/organic tandem solar cells and (b) pe...
Figure 8.6 (a) Schematic of the hybrid two‐step deposition method, (b) top‐v...
Figure 8.7 (a) Configuration of perovskite/Si tandem, (b) cross‐sectional SE...
Figure 8.8 Schematic of blade‐coated perovskite inks with F6TCNNQ additives ...
Figure 8.9 (a) Molecular structures of PSA, APSA, and KHQSA. (b) Schematic i...
Figure 8.10 (a,b) PL spectra with various incident lights for (a) control an...
Figure 8.11 (a,b) GIWAXS spectra of Pb‐Sn mixed perovskite films (a) w/o FPE...
Figure 8.12 (a–d) Conductive atomic force microscope (C‐AFM) images of (a) S...
Figure 8.13 Performance of hybrid ICLs on Perovskite/Si tandem solar cells: ...
Figure 8.14 (a) Device structure and corresponding cross‐sectional SEM image...
Figure 8.15 (a) Schematic of perovskite/organic tandem with effective compos...
Figure 8.16 (a,b) ToF‐SIMS 3D render overlay image of I‐Br distribution and ...
Figure 8.17 (a,b) DFT simulation of chemical interactions at the mp‐Al
2
O
3
/WB...
Figure 8.18 Operational stability of monolithic perovskite/silicon tandem so...
Figure 8.19 (a) Band diagrams of the ETL/perovskite contacts. (b) The cross‐...
Figure 8.20 (a) Schematic view of the perovskite/SHJ monolithic tandem cell ...
Figure 8.21 (a) Energy level alignment of various perovskite films and C60 l...
Chapter 9
Figure 9.1 Flowchart of PV module stability test for IEC 61215 standard.
Figure 9.2 Schematic illustration of the monolithic interconnection in a PSM...
Figure 9.3 Schematic of both internal and external encapsulation of perovski...
Figure 9.4 (a) Fabrication of perovskite solar modules by various deposition...
Figure 9.5 (a) Module fabrication processes; (b) module configuration, and s...
Figure 9.6 (a) The total power loss in a module as a function of the active‐...
Figure 9.7 The 1 m × 2 m perovskite solar modules from GCL.
Figure 9.8 Photo of 100 kW perovskite grid‐connected solar farm from Micoqua...
Figure 9.9 Perovskite/Si tandem module with 1.7 square meters (1 m × 1.7 m)....
Figure 9.10 Indoor light harvesting WBG‐perovskite cells to power wireless e...
Chapter 10
Figure 10.1 Growth of methylammonium lead iodide perovskite films from a pre...
Figure 10.2 (a) Measurement principle of ellipsometry. (b) Schematic for SE ...
Figure 10.3 (a) Absorption (black) and photoluminescence emission (red) spec...
Figure 10.4 Structures of electron‐only device (a) and hole‐only device (b),...
Figure 10.5 (a) Low‐magnification TEM image, (b,c) high‐resolution TEM image...
Figure 10.6 (a,b) AFM topography, (c,d) potential images and the correspondi...
Figure 10.7 GIWAXS images of (a) 3D/2D heterointerface and (b) 2D–3D‐F4TCNQ ...
Figure 10.8 GIXRD spectra at different tilt angles for 2θ at (a,b) 14.12° an...
Figure 10.9 Simulated molecular electrostatic potential (MEP) profiles of (a...
Figure 10.10 Ab initio molecular dynamics (AIMD) simulation of composite‐bas...
Figure 10.11 The defects passivation effect by calculated DOS for pristine 3...
Chapter 11
Figure 11.1 A schematic of R2R fabrication for large‐scale PSMs.
Figure 11.2 Human health characterization factors expressed in DALYs per kg ...
Figure 11.3 A process of Pb components and glass/TCO substrates recycling fr...
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Begin Reading
Index
End User License Agreement
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Composites‐Based Perovskite Solar Cells
Yoon-Bong Hahn, Yousheng Wang, and Tahmineh Mahmoudi
Authors
Yoon‐Bong Hahn
Jeonbuk National University
567 Baekje‐daero, Deokjin‐gu
Jeonju
54896, South Korea
Yousheng Wang
Jinan University
855 Xingye Avenue East
Panyu District
Guangzhou
510632, China
Tahmineh Mahmoudi
RMIT University
124 La Trobe Street
Melbourne
VIC 3001, Australia
Cover Image: © sutadimages/Shutterstock
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Print ISBN: 978‐3‐527‐35293‐7
ePDF ISBN: 978‐3‐527‐84452‐4
ePub ISBN: 978‐3‐527‐84453‐1
oBook ISBN: 978‐3‐527‐84454‐8
Preface
To meet the rapidly growing global energy demand, building an ecofriendly sustainable energy conversion and storage system is one of the great challenges of our time, leading both academia and industry to seek alternative and renewable energy solutions. Solar energy is the richest and the most green energy source on the planet, thus evaluating that photovoltaic (PV) technology is the most effective and promising technology. Among solar cells, recently perovskite PVs have emerged as a promising candidate for the next‐generation solar cell industry with an unprecedented rise of efficiency over 26%. However, the lack of stability of perovskite materials is a well‐known bottleneck in the commercialization of perovskite solar cells (PSCs). To solve this problem, many research groups around the world have studied various methods to develop reliable PSCs in terms of efficiency and stability. It is worth noting that both efficiency and stability are related to materials used to fabricate PSCs. Hence, in order to resolve the instability problems of PSCs with high efficiency, development of robust materials that can improve their chemical, electrical, optical, and thermal properties is of critical importance.
Recently, it has been reported that composite materials are suitable for solving the stability issues of PSCs. This book addresses the principles and materials for the development of composites‐based PSCs (CPSCs) and provides detailed descriptions of the functional composite materials that can be used for light‐absorbing, charge‐conducting, and interfacial layers of CPSCs. It will appeal to graduate‐level students and researchers interested in the practical use of perovskite PVs.
Chapter 1 introduces why the CPSCs are needed to solve problems related to power conversion efficiency and device stability, as well as the development strategy of CPSCs and the manufacturing strategy of highly stable and efficient CPSCs with perovskite‐based composite and interface engineering. Chapter 2 presents the optical and electrical properties of perovskites including three‐dimensional, two/low‐dimensional and single‐crystal perovskites, the typical growth dynamics of 3D perovskite crystals, the development history, the working principles, and device configurations of perovskite PVs.
Chapter 3 describes fundamentals and benefits of functional composite materials and introduces various kinds of composite materials for applications to active layer, hole‐ and electron‐transport layers, and electrodes of PSCs. Chapter 4 explains how the external factors such as moisture, light, and heat cause degradation of perovskite and interface, then discusses the defects formation mechanism in the solution‐processed perovskite thin films. This chapter further explores how the defects induce the perovskite instability and efficiency loss, followed by methods to improve materials and device stability without sacrificing efficiency.
Chapter 5 introduces composite‐based charge‐transport and interfacial materials. Efficient interface engineering methods with organic‐, inorganic‐, and carbon‐based composite materials for charge‐transport layers and interfacial layers are presented in detail. Chapter 6 presents a concept of composite‐based hybrid Pb‐perovskites, including organic additive‐based perovskite composites, inorganic additive‐based perovskite composites, 2D/3D heterostructure perovskite composites, quantum dot additive‐based perovskite composites, etc. Moreover, the mechanism of additives‐induced growth of perovskite crystals, mitigation of lattice distortion and ions migration, and passivation of film defects as well as the optical and electrical properties of composite‐based Pb‐perovskite films are discussed in detail.
Chapter 7 introduces the strategic implementation of additive engineering technique, which is a key to unlocking the full potential of Sn‐based PSCs, paving a way for sustainable high‐performance PV technologies. Chapter 8 provides information on the composites‐based hybrid perovskite materials for application to tandem solar cells (TSCs). The theoretical efficiency limit for two‐terminal and four‐terminal TSCs, the device configurations of a perovskite‐based TSC, and the progress and prospect of TSCs are presented.
Chapter 9 presents a comprehensive analysis of the path to commercialization of PSCs. First, briefly introduce the stability and encapsulation issues of perovskite‐based modules in their current state of development. Then up‐scaling, device design, and assessment methods of modules are discussed, with respect to scalable fabrication of high‐quality perovskite films, module fabrication process and characterization, as well as the status of solar module production, market prospect, and future challenges.
Chapter 10 introduces the characterization methods for CPSCs, which are indispensable tools in the advancement of CPSCs, offering critical insights into their optical, electrical, and structural properties toward sustainable and efficient PV applications. Chapter 11 presents perspectives of composites‐based PSCs and explores future work on developing green, highly efficient, and large‐scale PV products, which include scalable deposition techniques for all device layer stacks, green production technology, and recycling of perovskite solar products, etc.
Last but not least, our special thanks to the Wiley‐VCH GmbH for their continuous support and guidance. We also thank the publishers and authors who kindly permitted reprint of their work and acknowledge the National Research Foundation of Korea (2021R1A2C2013426) for supporting our CPSC research, which produced many useful data for writing this book. YW acknowledges partial support by Graduate textbook project of Jinan University (2023YJC009).
July 2024
Yoon‐Bong Hahn
Yousheng Wang
Tahmineh Mahmoudi
1Introduction – Why Composites‐Based Perovskite Solar Cells?
1.1 Need to Develop Composites‐Based Perovskite Solar Cells
Global electricity demand has continued to increase at a higher rate than the rate of global energy production. Compared to fossil fuels that produce huge amounts of carbon and cause global warming, the development of technologies related to energy conversion and storage for various clean and renewable energy resources such as solar, wind, hydro, and biomass is a big challenge of our time. Among the renewable energy resources, solar energy is the richest and the most eco‐friendly energy source on the planet that can supply the growing electricity demand, evaluating that photovoltaic (PV) technology is the most effective and promising technology. The solar PV industry is a vast field with various solar cells divided into several generations.
Silicon‐based solar cells, classified as first generation, are the most common type of PV with a market share of 95%. Crystalline silicon solar cells have many benefits, such as high efficiency of more than 20%, nontoxic material, good photoconductivity and stability, resistant to corrosion, long lifetime span of over 25 years, low maintenance, and versatile applications. However, due to the complex processes of manufacturing crystalline silicon and the use of pricey and high quality of silicon, the silicon solar cell panels are quite expensive. By contrast, thin‐film solar panels, classified as second generation, are lighter, less expensive, and more flexible than the silicon solar panels, allowing for easier installation in versatile applications.
Among the thin‐film solar cells, made with newer and less established materials, are classified as third generation or next generation. The emerging third‐generation solar cells include innovative technologies, such as perovskite, dye‐sensitized, quantum‐dot, organic, and semiconducting compound‐based (e.g. CZTS, CZTSe, CIGS, and CdTe) thin‐film solar cells. Among the third‐generation solar cells, perovskite solar cells (PSCs) have emerged as a promising candidate for the next‐generation solar cell industry with an unprecedented rise of power conversion efficiency (PCE) exceeding 26%. It is also worth noting that the best PCEs of tandem cells are 29.1% and 33.9%, respectively, with perovskite tandem cell and perovskite/Si (two terminals) tandem cell [1].
In PSCs, light‐harvesting material is the perovskite that has the same crystal structure as the naturally occurring mineral calcium titanium oxide (CaTiO3) with an ABX3 crystal structure (see Chapter 2). It is worth noting that perovskites have remarkable characteristics for PV applications, such as direct bandgap, broad light‐harvesting ability, high defect tolerance ability, long charge carrier diffusion length, and cost‐effective easy fabrication. However, the lack of stability of perovskite materials is a well‐known problem that degrades the performance of PSCs. One of the main reasons for instability is that the perovskite materials contain unstable elements due to extra weak interactions, such as van der Waals force and weak hydrogen bonds [2]. Moreover, the stability of perovskite technology depends on its environmental factors, such as humidity, heat accumulation, and continuous irradiation of sunlight [3]. Thus, the degradation of device performance is caused by external and internal factors. The former includes air‐, thermal‐, and photo‐induced instability, and the latter includes intrinsic factors such as ions migration and interfacial recombination attributed to grain boundaries, contact interface, and vacancies.
Solution‐processed polycrystalline perovskite thin films present parasitic bulk and interface defects during the crystal growth process. In addition, their bulk and interface trap densities are higher than that of single‐crystal perovskites. These bulk and interface defects often cause undesirable deep‐level traps: undercoordinated Pb2+ ions, undercoordinated halide ions, metallic lead clusters, and intrinsic point defects (such as ion vacancies and Pb‐I antisite defects) [4, 5]. Therefore, defects at the bulk grain boundaries (GBs) and at interfaces of perovskite polycrystalline thin films become major sources to induce shallow trap states and localize charge carriers through nonradiative recombination, which are detrimental to the efficiency and stability of PSCs. To overcome these defects, achieving a high‐quality perovskite film and its defect passivation is crucial. Thus, tremendous efforts have been dedicated toward minimizing the perovskite GBs and surface/interface defects by additive engineering to induce the formation of perovskite‐based composites.
As the stability issues are mostly related to materials in terms of chemical, optical, and mechanical properties, to resolve the instability problems of PSCs, robust materials that can improve their chemical, electrical, optical, and thermal properties should be developed. The development of perovskite‐based composites with composition engineering has been considered an efficient strategy to stabilize the structures of perovskite and further improve their optical and electronic properties. Recently, it has been reported that composite materials are efficient for solving or alleviating the stability issues of PSCs [6–20]. A composite material is a combination of two or more materials having different chemical and physical properties. Compared to traditional materials, composites can improve the properties of base materials and can be applied in many situations. Composite materials have advantages such as design flexibility, specialized chemical and physical properties, and resistance to a wide range of chemicals. Therefore, they may give benefits to solve critical issues related to the efficiency and operational stability of PSCs.
Figure 1.1 illustrates the development strategy of composites‐based perovskite solar cells (CPSCs) schematically, in which composite materials can be used for active layer (AL) and charge‐transport layers. The incorporation of composite materials can significantly improve the PCE and stability of single‐junction solar cells as well as of tandem cells. This strategy is applicable to the development of both Pb‐based and Pb‐free CPSCs. To enhance the PCE and stability, it is crucial to design optimal light‐absorbing and charge‐transport materials along with interface engineering and additive engineering.
Figure 1.1 Schematic illustration of the development strategy of composites‐based perovskite solar cells.
1.2 Fabrication Strategy for Composites‐Based Perovskite Solar Cells
In addition to stabilizing the AL with composite‐based perovskites, interface engineering plays a crucial role because the interface contacts between the light‐absorbing and charge‐conducting materials are worthy of further study toward commercialization of PSCs in terms of interfacial energetics, charge transfer, and recombination kinetics, and interfacial degradation [17, 21, 22]. A typical PSC configuration consists of a perovskite film sandwiched between electron‐transport layer (ETL) and hole‐transport layer (HTL), which can form ETL/perovskite and perovskite/HTL interfaces, respectively. The carrier transport contacts and their interfaces determine device performance, including PCE, long‐term stability, and J–V hysteresis. The separated holes and electrons have to transport across the interfaces in the device, but charge loss often occurs because of possible interfacial defects. GBs within the AL separating perovskite grains also induce recombination and provide moisture and oxygen penetration pathways, resulting in J–V hysteresis, device performance loss, and deterioration. Particularly, the interfacial degradation between absorber and contact materials has become a critical intrinsic factor, resulting in poor stability of PSCs. The ETL/AL and AL/HTL contacts may induce interfacial collapse of the perovskite structures because groups of perovskite atoms or interfaces may move or be disordered under real operation conditions such as humidity, air, heat, and UV [17, 23, 24]. Therefore, interfacial engineering is important to improve interfacial contact by interface modifications such as interlayers or multilayers, which form a stabilized interface between active and charge‐collecting layers, ultimately improving the device performance and stability. The purpose of interface engineering is to modify perovskite contact and crystal growth, tune energy band alignment for reducing electron or hole transport barrier, lower recombination, enhance charge carriers transfer, and suppress interfacial defects and ions migration.
Figure 1.2 presents an efficient strategy for fabricating highly stable and efficient CPSCs with the inclusion of functional perovskite composite materials and interface engineering. The composite materials include mixed cations and halides perovskite with composition engineering, 2D/3D perovskite composites, organic material–perovskite composites, and inorganic material–perovskite composites. The perovskite‐based composites can significantly regulate the optical and electronic properties of perovskites and facilitate the growth of perovskite grains and carriers transport, but they inhibit ion migration and reduce defect formation. Besides, the organic or inorganic materials incorporated in perovskite composites also remarkably enhance stability because of their protective effects and strong chemical interaction and cross‐linking behavior. The 2D/3D perovskite composites significantly enhance device stability without sacrificing the considerable performance of PSCs. Furthermore, the organic or inorganic substances contained in perovskite composites significantly improve their stability thanks to their protective effects and strong chemical interactions and crosslinking with perovskite molecules. In addition, the strategy of interface stabilization can improve interfacial contact, assist the growth of perovskite grains, passivate perovskite film surface, facilitate charge transport, suppress ions migration, and protect perovskite films from water and oxygen molecules. Thus, it can be concluded that the strategy utilizing both perovskite‐based composites and interfacial engineering is one of the most efficient ways to achieve high‐efficiency and stable perovskite photovoltaics.
Figure 1.2 Schematic illustration of an efficient strategy for the fabrication of highly stable and efficient PSCs: inclusion of perovskite‐based composites and interface engineering.
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2Hybrid Perovskites and Solar Cells
2.1 Perovskite Materials
A perovskite is a material that has the same crystal structure as the naturally occurring mineral calcium titanium oxide (CaTiO3). It was first discovered by German mineralogist Gustav Rose in 1839 and was named after Russian mineralogist L. A. Perovski. Generally, a perovskite has a three‐dimensional (3D) structure ABX3, where the cation A is stabilized in a cubo‐octahedral cage formed by the 12 nearest X anions, and the cation B coordinates with the six nearest X anions to form octahedral geometry [1]. Usually, artificial organic–inorganic hybrid perovskites are a broad class of materials adopting a general chemical formula of ABX3 (A = monovalent cation, such as FA+, MA+, Cs+; B = metallic divalent cations, such as Pb2+ and Sn2+; X = halide anions such as I–, Br–, and Cl–) as shown in Figure 2.1a. To establish a stable and cubic phase, the tolerance factor (t) of perovskite should be in a range of 0.8 ≤ t ≤ 1.0. The value of t can be calculated by the Goldschmidt equation , where r is the ionic radius [3].
Figure 2.1 (a) Typical 3D hybrid perovskite structure ABX3 (A = organic cation, B = metal cation, and X = halide anion) and (b) molecular orbitals for Pb‐ and Sn‐based perovskites.
Source: Adapted from [2].
2.1.1 Three‐Dimensional Perovskites
2.1.1.1 Lead‐Based Perovskites
As discussed above, the hybrid perovskites have a general chemical formula of ABX3. The B site metallic divalent cations such as Pb, Sn, and Ge ions but Pb‐based perovskites are still indispensable to ensure excellent photoelectric properties. Although molecular orbitals of APbI3 and ASnI3 are similar as shown in Figure 2.1b, the band edges in APbI3 are more strongly bound than those of ASnI3, thus leading to the difference of the band edge positions (band offsets) [4]. Since the energy levels of the Pb 6s and Pb 6p atomic orbitals are both lower than those of the Sn 5s and Sn 5p orbitals, the CBM and VBM of APbI3 are both higher. Compared to the inert electrons in Pb 6s orbitals, the active electrons in high‐energy Sn 5s orbitals are unstable and easy to lose. Besides, the redox potential of Sn2+/Sn4+ (0.15 V) is lower than that of Pb2+/Pb4+ (1.60) [2]. That is why Sn2+ is easily oxidized to Sn4+ under ambient conditions, leading to high trap densities, short charge carriers, and diffusion lengths in ASnI3.
As it is well known, pure Pb‐based hybrid perovskites show intriguing optical and electronic properties, such as high carrier mobility and absorption coefficient, tunable band gap, long charge diffusion lengths, low exciton binding energy, and broad light absorption wavelength [5–8]. With the advent of solid‐state pure Pb‐based perovskite solar cells (PSCs) since 2012 [9, 10], it has achieved great success in the field of third‐generation/emerging photovoltaics [11–15].
2.1.1.2 Lead–Tin‐Mixed Perovskites
Due to the similar outer electronic structure, Sn can be used to partially replace Pb to develop a narrow bandgap Pb–Sn‐mixed perovskite (∼1.17 eV). Low‐bandgap Sn–Pb perovskites with mixed organic cations (MA/FA) also show high‐quantum efficiency and decent storage stability because of the low bandgap of ∼1.2 eV and long carrier lifetime over hundreds of nanosecond (ns) [16]. The band gap and absorption wavelength of Pb–Sn‐mixed perovskites can be remarkably adjusted by Sn‐doping [17]. Among various compositions, (FASnI3)1‐x(MAPbI3)x showed good optoelectronic properties with the highest performance for low bandgap stable perovskite solar cells [18]. Halide (Cl and Br) incorporation in Pb–Sn‐based perovskite helps to passivate grain boundary via improved electronic properties and reduced recombination, leading to high power conversion efficiencies (PCEs) [19]. Although the stability of Pb–Sn‐mixed perovskites is poor compared to pure Pb‐based perovskites, they are promising to combine with wide‐gap perovskites yielding all‐perovskite tandem solar cells with higher efficiency. For example, 2‐T monolithic all‐perovskite tandem cell using low‐bandgap Sn–Pb PSCs was first reported by using a FA0.83Cs0.17Pb(I0.7Br0.3)3 (Eg = 1.8 eV) top cell and FA0.75Cs0.25Sn0.5Pb0.5I3 (Eg = 1.2 eV) bottom cell, achieved a PCE of 19.1% with high Voc of 1.81 V and Jsc of 14.8 mA/cm2[20]. More importantly, all‐perovskite tandem cells based on Sn‐Pb perovskites with an ideal bandgap can obtain a theoretical efficiency of over 40%, which is higher than single‐junction PSCs with around 32% efficiency limit [21, 22].
2.1.1.3 Tin‐Based Perovskites
Although Pb or Pb–Sn‐based perovskites have shown great potential for high‐performance single‐junction or multi‐junction solar cells, the lead leakage from PSCs can be toxic to the environment, humans, and other species, which may impede the commercialization of this technology. With this in mind, Pb‐free perovskites, such as Tin (Sn), germanium (Ge), antimony (Sb), and bismuth (Bi), have been widely studied for solar cell applications though they have shown poor efficiency and stability. Among them, Sn has a crystal structure similar to that of Pb and is considered the most promising candidate to replace Pb. According to the Shockley– Queisser (S–Q) limit, pure Sn‐based PSCs also have a theoretical PCE of 33.4%, even higher than Pb‐based PSCs with a PCE of 32.1% (Figure 2.2, left) [23]. Due to the excellent optoelectronic properties including large carrier mobility and strong light absorption coefficients, the theoretical efficiency of Sn‐PSCs can be >33% with an ideal Voc of 1.1 V and a Jsc of 32 mA/cm2 (Figure 2.2, right). Unluckily, Sn‐PSCs have achieved a certified record PCE of 14.6% so far [23], which is only 43.7% of the theoretical maximum PCE. The lower PCEs are mainly attributed to the following reasons:
(1) Ease oxidation of Sn
2+
as discussed in
Section 2.1.1.1
.
(2) Uncontrollable crystallization of ASnI
3
: due to the active 5s electrons in Sn, SnI
2
has a higher Lewis acidity than that of PbI
2
, thus the reaction speed between SnI
2
and Lewis bases such as MAI and FAI is faster than that of PbI
2
[22]
.
(3) Sn vacancy defects: because of the higher energy level of Sn 5s, the Sn‐I bonds are easy to break, leading to the formation of Sn vacancy defects
[24]
. Meanwhile, the weak bond of Sn−I also facilitates the formation of H−I and Sn−O bonds under ambient conditions (H
2
O and O
2
)
[25]
.
(4) Interface recombination: due to the easy oxidation of Sn
2+
, the film surface defects are easily formed. Thus, a protection layer is needed to suppress the interface recombination
[26]
.
(5) Band alignment mismatch: The unique band structure of Sn‐perovskite requires a distinctive structure design to reduce energy band alignment mismatch. An inverted structure is highly desired due to better compatibility and band alignment
[27]
.
Figure 2.2 Shockley–Queisser efficiency limit, and Voc and Jsc.
Reproduced with permission from [22]. Copyright 2021, American Chemical Society.
2.1.1.4 All Inorganic Perovskites
All‐inorganic halide perovskitescan be formed when organic cation site A is replaced by inorganic cation Cs in ABX3, such as CsPbI3, CsPbBr3, and CsPbCl3. Note that the cubic α‐phase CsPbI3 is the most prominent candidate for photovoltaic applications due to the appropriate Eg of 1.73 eV. However, the cubic α‐phase CsPbI3 is only stable at a high temperature, and it rapidly transforms into a yellow orthorhombic non‐perovskite δ‐phase with Eg of 2.82 eV, resulting in poor photovoltaic properties at room temperature [28]. Although CsPbBr3 presents the best phase stability among all Cs‐based all inorganic perovskites, the wide Eg of 2.3 eV limits the photocurrent and thus makes it difficult to achieve a higher PCE in solar cells. As reported, partial substitution of iodine (I) with bromide (Br) can build mixed‐anion CsPbI2Br (Eg = 1.92 eV) and CsPbIBr2 (Eg = 2.05 eV). However, such higher bandgaps severely limit the photocurrent, leading to lower PCEs [29]. Therefore, in‐depth experimental and theoretical studies on the chemical and physical properties of all inorganic perovskites are needed to further improve the efficiency and the long‐term stability of inorganic photovoltaics under operational conditions.
2.1.2 Low‐Dimensional Perovskites
The 3D crystal perovskites present poor stability when exposed to ambient conditions. The instability is mainly attributed to organic compounds and phase transformation. However, perovskites are endowed with dimensional tailoring properties for more stable low‐dimensional structures. For instance, 2D perovskites with natural multi‐quantum‐well structures have become a class of emerging optoelectronic materials due to their unique properties, such as impressive chemical diversity, tunable optoelectronic properties, and superior structure stability. 2D perovskites have the general formula R2An‐1BnX3n+1, where R is a bulky organic cation that plays the role of spacer between the inorganic framework, A is a small monovalent cation (such as FA and MA), B is a divalent metal cation (such as Pb2+ and Sn2+), X is a halide anion, and n is the thickness of inorganic perovskite layers between adjacent organic spacer layers.
2.1.2.1 Ruddlesden–Popper (RP) 2D Perovskites
Adopting alkylammonium cations (such as butylammonium (BA) and phenylethylamine (PEA)) in the R position results in a layered two‐dimensional (2D) perovskite structure (RP phase). As shown in Figure 2.3 (top) [30], a van der Waals gap and hydrogen bonds can be formed in the spacer layer in the RP phase (when n = 3). The spacers used in 2D RP perovskites mainly include aliphatic and aromatic spacer cations. Properties of 2D RP perovskites such as the energy levels, exciton binding energy, and charge transport mobility can be tuned by changing the organic spacers and the n‐values. As shown in Figure 2.3 (bottom), the quasi‐BA2MAn‐1PbnI3n+1 can give various bandgaps and optical properties depending on the number of layers. When n ≤ 2, the 2D perovskites have a high bandgap and high exciton binding energy up to hundreds of meV. Thus, the 2D perovskites are difficult as light absorbers and unsuitable for PVs. However, they exhibit strong excitonic behavior attributed to quantum confinement effects, which can yield high photoluminescence and make them suitable for LED applications.
Figure 2.3 Band gaps of 2D (n = 1) and quasi‐2D BA2MAn−1PbnI3n+1 (BA: butylammonium) for different n values and corresponding to their alignment of the energy levels and band gaps.
Source: Adapted from [30].
2.1.2.2 Dion–Jacobson (DJ) 2D Perovskites
In contrast to 2D RP perovskites with monovalent spacers (Figure 2.4, top), DJ type perovskite structure has a divalent interlayer spacers (such as propane‐1,3‐diammonium (PDA) and butane‐1,4‐diammonium (BDA)) to bridge the neighboring inorganic slab with hydrogen bonding by monolayer bivalent organic cations, removing the van der Waals gap (n = 3, Figure 2.4, bottom) [8]. The divalent spacers with similar lengths in 2D‐DJ perovskites exhibit shortened interslab distance and form a more rigid structure, which could reduce the charge transport barrier. Also, 2D‐DJ perovskites have less lattice distortion than the 2D‐RP type, leading to better optoelectrical performance. Therefore, DJ perovskites possess better stability compared to RP perovskites. For example, to remove the van der Waals gap in 2D perovskites, Li et al. developed DJ phase 2D perovskites by incorporating diammonium cations (PDA) into MAPbI3[32]. Compared to RP 2Dperovskites incorporated propylamine (PA) cations‐based solar cells (PCE = 8.8%), DJ phase 2D perovskites‐based solar cells showed improved efficiency of 13.3%. Also, DJ‐2D PSCs showed better device stability than the RP counterpart‐based device due to strengthening the 2D layered perovskite structure by the hydrogen bonding interactions.
Figure 2.4 The 2D structure of Ruddlesden–Popper (RP) (top) and Dion–Jacobson (DJ) perovskites, n = 3, bottom).
Source: [31]/John Wiley & Sons/CC BY 4.0.
2.1.2.3 One‐/Zero‐Dimensional (1D/0D) Perovskites
1D/0D perovskites can be synthesized by exceptional structural tunability with proper components. As shown in Figure 2.5, stable 1D structures have the metal halide octahedrons connected in a chain by means of shared corners, edges, or faces, and surrounded by organic cations; 0D perovskites have individual metal halide octahedral anions or metal halide clusters which are completely surrounded and isolated by the organic cations [33]. Such 1D/0D perovskites show unique photophysical properties owing to strong quantum confinement, high exciton binding energy, and largely Stokes‐shifted broadband emissions from self‐trapped excitons, resulting in great potential for LEDs, photodetectors, etc. [34]. For example, Yuan et al. reported 1D‐perovskites C4N2H14PbBr4, in which the edge‐sharing halide octahedral chains [PbBr42−] are surrounded by the organic cations C4N2H14 2+ to form quantum wires. Such 1D‐based LEDs give efficient bluish white light emissions with 20% photoluminescence quantum efficiencies [35]. Besides, 1D/0D perovskites also are selected as a passivated or protected layer for highly efficient and stable PSCs due to their excellent material stability properties against humidity, light exposure, and heat stress [36, 37].
Figure 2.5 The structure of 0D and 1D perovskites.
Source: [33]/John Wiley & Sons/CC BY 4.0.
2.1.3 Single‐Crystal Perovskites
Compared with polycrystalline perovskites, single‐crystal perovskites without grain boundaries (GBs) show better optoelectronic properties, that is, extended absorption spectrum, lower band gaps, longer carrier diffusion length, lower trap densities, and suppressed ion migration effect [38]. Due to the well‐aligned lattice structures and no GBs effect, the single‐crystal perovskites also show much‐enhanced device stability compared to their polycrystalline counterparts. More importantly, single‐crystal PSCs present a higher theoretical PCE and Jsc than polycrystalline PSCs [39], as shown in Figure 2.6. However, the efficiency of single‐crystal PSCs is lower than that of polycrystalline PSCs partly because of challenges in crystal growth, thickness control, and solar cell device integration. Besides, single‐crystal perovskites also present great potential in other fields, such as photodetector, laser, and LED [40].
Figure 2.6 The S–Q theoretical limit for the PCE and Jsc of single‐junction solar cells as a function of the bandgap for single‐crystal GaAs and FA0.6MA0.4PbI3, and polycrystalline FAPbI3.
Source: Reproduced with permission from [39]/Royal Society of Chemistry.
2.1.4 Dynamics of Perovskite Crystal Growth
As it is well known, the crystal morphology of the perovskite absorber layer remarkably affects the photovoltaic performance of PSCs. Unluckily, 3D perovskite films that are generally obtained by a simple solution‐processed deposition technology always present poor morphologies with incomplete surface coverage and many voids, which are detrimental to solar cell efficiency and stability because of inefficient light‐harvesting, leakage paths, moisture invasion, etc. [41]. Such film defects also provide a route to accelerate ion migration of halide anions (I−) and escape of organic cations (MA+ and FA+) from the perovskite absorber layer. Those factors not only lead to notorious J‐V hysteresis in solar cells but also erode top electrodes and finally burn in the structure of perovskites [42]. Furthermore, the inhomogeneity of perovskite films becomes worse while enlarging area of films by scalable fabrication methods [43, 44]. Thus, understanding the growth and formation mechanisms of perovskite crystals is of paramount importance to obtain high‐quality and homogenous large‐area perovskite films by scalable fabrication technology.
The formation of polycrystalline perovskite films from precursor solutions generally relates to three important steps, that is, nucleation, growth and diffusion of the crystals. Figure 2.7a systematically presents the process of perovskite film formation from a wet film to a complete film during heat treatment. A La Mer mechanism has been applied to elaborate the nucleation and crystallization of perovskite films by solution coating methods, as shown in Figure 2.7b. During the evaporation of the solvents (such as DMF and DMSO) in stage I, the solution concentration increases to reach supersaturation concentration (Cs) at a time of t1; meanwhile, the nuclei start to take place until the critical concentration (Cc) at a time of t2; then, both nucleation and crystal growth occur in stage II; in stage III, the solvent evaporation is slower than the consumption of solute, thus the solution concentration is lower than the Cs, where only growth of the formed nuclei happens without formation of additional nuclei [45]. According to the classical theory of homogenous nuclei formation, the nucleation rate can be determined based on a critical free energy (ΔGc), as shown in Figure 2.7c. The nucleation rate depends on the number of nuclei (N), which can be described by using an Arrhenius equation [45, 46]:
where N, t, A, kB, and T represent the number of nuclei, nuclei time, pre‐exponential factor, Boltzmann's constant, and temperature, respectively. The critical free energy (ΔGc) is further determined by surface energy γ, mole volume ν, and supersaturation of solution S according to the following equation [45, 46]:
Figure 2.7 (a) The nucleation and growth processes of perovskite films. (b) Lar Mer model for nucleation and growth of perovskite films, Cs, Cc, and Climit are supersaturation concentration, critical concentration, and limiting supersaturation concentration of a precursor solution, respectively. (c) Free energy diagram of nucleation, ΔG, ΔGs, ΔGν, ΔGc, and rc are total free energy, surface free energy, bulk‐free energy, critical free energy, and critical radius of nucleus.
Source: Adapted from [45].
During the film formation, the free energy of heterogeneous nucleation is equal to the energy formation of homogenous nucleation and a correction term ∅ [45, 46].
The correction term ∅ is determined by the contact angle of the solution on a substrate (θ) according to the following:
equation [45, 46]:
According to the above equations, perovskite nucleation depends on surface energy, temperature, supersaturation level, and wettability of the substrate. According to previous research experience on the fabrication of perovskite films, the supersaturation level is an important factor that remarkably affects the perovskite crystal size and growth quality.
