The rise of flexible perovskite photovoltaics

In a recent article from Joule, Shin and co-workers elucidated a multi-layer electron transport layer to reduce the efficiency-stability tradeoff of flexible perovskite solar modules. A record-certified power conversion efficiency of 16.14% (900 cm2) with improved operational stability was obtained, highlighting the potential for further solar cells' performance. In a recent article from Joule, Shin and co-workers elucidated a multi-layer electron transport layer to reduce the efficiency-stability tradeoff of flexible perovskite solar modules. A record-certified power conversion efficiency of 16.14% (900 cm2) with improved operational stability was obtained, highlighting the potential for further solar cells' performance. Halide perovskites possess optical and electrical properties that are ideal for optoelectronic devices. These materials generally have a high absorption coefficient, high carrier mobility, long carrier diffusion length, and excellent defect tolerance.1Song F. Zheng D. Feng J. Liu J. Ye T. Li Z. Wang K. Liu S. Yang D. Mechanical Durability and Flexibility in Perovskite Photovoltaics: Advancements and Applications. Advanced Materials n/a.20242312041https://doi.org/10.1002/adma.202312041Crossref Google Scholar As of 2023, the power conversion efficiency (PCE) of single-junction perovskite solar cells (PSCs) has exceeded 26%,2Best Research-Cell Efficiency ChartNational Renewable Energy Laboratory.https://www.nrel.gov/pv/cell-efficiency.htmlDate: 2024Google Scholar which is the highest value reported so far among all thin-film photovoltaic (PV) technologies. PSCs have garnered interest, particularly in flexible PSCs (f-PSCs), which have demonstrated promise for applications such as portable chargers, building-integrated photovoltaic (BIPV), spacecraft, and wearable devices.3Li M. Zhou J. Tan L. Li H. Liu Y. Jiang C. Ye Y. Ding L. Tress W. Yi C. Multifunctional succinate additive for flexible perovskite solar cells with more than 23% power-conversion efficiency.Innovation. 2022; 3100310https://doi.org/10.1016/j.xinn.2022.100310Abstract Full Text Full Text PDF Scopus (70) Google Scholar In 2013, Kumar et al. documented the development of low-temperature solution-processed f-PSCs. This f-PSC demonstrated a PCE of only 2.62%, representing a milestone for f-PSCs.4Kumar M.H. Yantara N. Dharani S. Graetzel M. Mhaisalkar S. Boix P.P. Mathews N. Flexible, low-temperature, solution processed ZnO-based perovskite solid state solar cells.Chem. Commun. 2013; 49: 11089-11091https://doi.org/10.1039/C3CC46534ACrossref PubMed Scopus (0) Google Scholar Subsequently, researchers have dedicated to augmenting the PCE and flexural resilience of f-PSCs, including additive engineering, interfacial engineering, etc.,1Song F. Zheng D. Feng J. Liu J. Ye T. Li Z. Wang K. Liu S. Yang D. Mechanical Durability and Flexibility in Perovskite Photovoltaics: Advancements and Applications. Advanced Materials n/a.20242312041https://doi.org/10.1002/adma.202312041Crossref Google Scholar resulting in the highest PCE of f-PSCs to 25.09%.5Ren N. Tan L. Li M. Zhou J. Ye Y. Jiao B. Ding L. Yi C. 25% — Efficiency flexible perovskite solar cells via controllable growth of SnO2.iEnergy. 2024; 3: 39-45https://doi.org/10.23919/IEN.2024.0001Crossref Scopus (0) Google Scholar The commercialization of PSCs is progressing rapidly due to the increasing efficiency and stability observed at the module level. Nevertheless, converting small-area cells into large-area modules for f-PSCs has exhibited comparatively lower success levels than rigid ones. Since the first flexible perovskite solar modules (f-PSMs) with an active area of 8 cm2 (PCE, 3.1%)6Di Giacomo F. Zardetto V. D'Epifanio A. Pescetelli S. Matteocci F. Razza S. Di Carlo A. Licoccia S. Kessels W.M.M. Creatore M. Brown T.M. Flexible Perovskite Photovoltaic Modules and Solar Cells Based on Atomic Layer Deposited Compact Layers and UV-Irradiated TiO2 Scaffolds on Plastic Substrates.Adv. Energy Mater. 2015; 51401808https://doi.org/10.1002/aenm.201401808Crossref Scopus (246) Google Scholar were reported in 2015, the performance of f-PSMs (≥100 cm2) was only 15.5% (Figure 1),7Chung J. Shin S.S. Hwang K. Kim G. Kim K.W. Lee D.S. Kim W. Ma B.S. Kim Y.-K. Kim T.-S. Seo J. Record-efficiency flexible perovskite solar cell and module enabled by a porous-planar structure as an electron transport layer.Energy Environ. Sci. 2020; 13: 4854-4861https://doi.org/10.1039/D0EE02164DCrossref Google Scholar which was primarily attributed to uneven film formation on flexible substrates and the substrate's inability to survive the acidic environment and high temperatures.8Xu W. Chen B. Zhang Z. Liu Y. Xian Y. Wang X. Shi Z. Gu H. Fei C. Li N. et al.Multifunctional entinostat enhances the mechanical robustness and efficiency of flexible perovskite solar cells and minimodules.Nat. Photonics. 2024; 18: 379-387https://doi.org/10.1038/s41566-023-01373-zCrossref Scopus (2) Google Scholar In addition, one of the drawbacks of halide perovskites is that their chemical composition entails toxic lead. Thus, how to reduce lead toxicity should also be considered during the industrial of Pb-base perovskites. In a recent work published in Joule, Shin and co-workers found that the efficiency and stability of f-PSCs were compromised due to an imbalance between surface coverage and charge-transporting properties when employing colloidal SnO2 nanoparticles as an electron-transport layer (ETL) through the cyclic voltammetry (CV) and time-resolved photoluminescence (TR-PL) test.9Lee D.S. Kim K.W. Seo Y.-H. Ann M.H. Lee W. Nam J. Chung J. Seo G. Nam S. Ma B.S. et al.Overcoming stability limitations of efficient, flexible perovskite solar modules.Joule. 2024; 8: 1380-1393https://doi.org/10.1016/j.joule.2024.02.008Abstract Full Text Full Text PDF Scopus (0) Google Scholar They first fabricated a series of PSCs according to the thickness of SnO2 ETL (∼17, ∼25, ∼35, and ∼85 nm) by controlling the SnO2 colloidal solution concentration. The device based on thinner SnO2 ETL (17 nm) exhibited comparatively higher efficiency but demonstrated poor photostability. Conversely, the device based on thicker SnO2 (≥35 nm) ETL exhibited much lower efficiency but greatly improved photostability. They chose the 25 nm ETL named SL-25 to achieve a high efficiency. Then, they synthesized the rod-shaped SnO2 nanorods (1D-SnO2 NPs), recognized for their electron-transport capability, and spin-coated it onto the existing 25 nm SnO2 film, referred to as multi-layer (ML). Through this, they obtained a substantial reduction in the effective pinhole area in ETL, resulting in improved PCE and photostability on rigid devices. To showcase the potential of ML for the application of the flexible devices, they fabricated f-PSCs and f-PSMs based on corresponding ETLs. ML-based f-PSC demonstrated superior PCE compared to SL-based f-PSC, similar to rigid PSCs. They further applied ML to large-area f-PSMs (25 cm2). An improved PCE was observed in the ML ETL by its superior surface coverage and charge-transporting property. The creation of a shunt pathway from incomplete coverage, resulting in the current crowding effect, was seen through dark lock-in thermography (DLIT) imaging techniques and electroluminescence (EL) analysis. This phenomenon had the potential to affect the long-term operational stability significantly. Thus, they further proceeded with fabricating a larger f-PSM (900 cm2) and got a certified PCE of 16.43%, the highest PCE among large-area f-PSMs. The ML-based f-PSM demonstrated favorable bending stability, retaining roughly 96.2% of its initial values after undergoing 1,000 bending cycles. This work created an ML ETL to achieve the highest reported PCE on large modules with enhanced f-PSM's operational stability, which could also be applied in other perovskite-based optoelectronic devices such as light-emitting diodes and photodetectors. The ETL concept for minimizing the shunt path without reducing charge transport properties is a critical component that may help the f-PSMs succeed commercially. Nowadays, most of the f-PSMs are based on n-i-p structures. The multi-layer ETL/HTL should also be considered for extending p-i-n f-PSCs and flexible tandem PSMs. In addition, the fully continuous roll-to-roll (R2R) manufacturing techniques,10Weerasinghe H.C. Macadam N. Kim J.-E. Sutherland L.J. Angmo D. Ng L.W.T. Scully A.D. Glenn F. Chantler R. Chang N.L. et al.The first demonstration of entirely roll-to-roll fabricated perovskite solar cell modules under ambient room conditions.Nat. Commun. 2024; 15: 1656https://doi.org/10.1038/s41467-024-46016-1Crossref Scopus (0) Google Scholar should also be considered due to its high-volume and high-throughput manufacturing. Lastly, developing new encapsulation technology and preventing lead leakage should not be overlooked. With these technological advancements, it is anticipated that the commercial manufacturing of flexible perovskite photovoltaics will be imminent. The authors acknowledge support from the National Natural Science Foundation of China (52203237) and the Fundamental Research Funds for the Central Universities (000–0903069032). The authors declare no competing interests. Overcoming stability limitations of efficient, flexible perovskite solar modulesLee et al.JouleFebruary 29, 2024In BriefThis work highlights a breakthrough in flexible perovskite solar module (f-PSM) technology, addressing performance and stability issues. A novel multi-layer electron transport layer (ML ETL) overcomes efficiency-stability trade-offs, achieving high efficiencies of 22.9% on unit cells and 16.4% on large modules (900 cm2) while enhancing operational stability.