Perovskite solar cells (PSCs) are being rapidly developed at a fiery stage due to their marvelous and fast-growing power conversion efficiency (PCE). Advantages such as high PCE, solution processability, tunable band gaps, and flexibility make PSCs one of the research hot spots in the energy field. Flexible PSCs (f-PSCs) owing to high power-to-weight ratios can be promising candidates to serve as power sources in mobile energy systems, space energy systems, portable functional devices, and so on. Herein, we give a review on recent progress in f-PSCs involving flexible substrates and flexible transparent electrodes, performance enhancement by optimizing functional layers, large-scale fabrication techniques, flexibility promotion strategies, and their potential applications. Furthermore, perspectives are discussed on the future development of f-PSCs.

Flexible perovskite solar cells (f‐PSCs) have been attracting tremendous attention due to their potentially commercial prospects in flexible energy system and mobile energy system. Reducing the energy barriers and charge extraction losses at the interfaces between perovskite and charge transport layers is essential to improve both efficiency and stability of f‐PSCs. Herein, 4‐trifluoromethylphenylethylamine iodide (CF3PEAI) is introduced to form a 2D perovskite at the interface between perovskite and hole transport layer (HTL). It is found that the 2D perovskite plays a dual‐functional role in aligning energy band between perovskite and HTL and passivating the traps in the 3D perovskite, thus reducing energy loss and charge carrier recombination at the interface, facilitating the hole transfer from perovskite to the Spiro‐OMeTAD. Consequently, the photovoltaic performance of f‐PSCs is significantly improved, leading to a power conversion efficiency (PCE) of 21.1% and a certified PCE of 20.5%. Furthermore, the long‐term stability of f‐PSCs is greatly improved through the protection of 2D perovskite layer to the underlying 3D perovskite. This work provides an excellent strategy to produce efficient and stable f‐PSCs, which will accelerate their potential applications.

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With the rapid rise in perovskite solar cells (PSCs) performance, it is imperative to develop scalable fabrication techniques to accelerate potential commercialization. However, the power conversion efficiencies (PCEs) of PSCs fabricated via scalable two-step sequential deposition lag far behind the state-of-the-art spin-coated ones. Herein, the additive methylammonium chloride (MACl) is introduced to modulate the crystallization and orientation of a two-step sequential doctor-bladed perovskite film in ambient conditions. MACl can significantly improve perovskite film quality and increase grain size and crystallinity, thus decreasing trap density and suppressing nonradiative recombination. Meanwhile, MACl also promotes the preferred face-up orientation of the (100) plane of perovskite film, which is more conducive to the transport and collection of carriers, thereby significantly improving the fill factor. As a result, a champion PCE of 23.14% and excellent long-term stability are achieved for PSCs based on the structure of ITO/SnO2/FA1-xMAxPb(I1-yBry)3/Spiro-OMeTAD/Ag. The superior PCEs of 21.20% and 17.54% are achieved for 1.03 cm2 PSC and 10.93 cm2 mini-module, respectively. These results represent substantial progress in large-scale two-step sequential deposition of high-performance PSCs for practical applications.

The morphology and interface of perovskite film are very important for the performance of perovskite solar cells (PSCs). The quality of perovskite film, fabricated via two-step spin-coating process, is significantly influenced by the morphology and crystallinity of PbI2 film. With the addition of additive dimethyl sulfoxide (DMSO) into the PbI2 precursor, the roughness and trap-state density of perovskite film have been significantly reduced, leading to the excellent contact between perovskite layer and subsequent deposited carrier transport layer. Accordingly, the planar heterojunction PSCs with an architecture of ITO/SnO2/perovskite/PTAA/Ag show an efficiency up to 19.02%. Furthermore, PSCs exhibit promising stability in air with a humidity of ∼ 45%, and retain 80% of initial efficiency after being exposed to air for 400 h without any encapsulation.

Perovskite solar cells (PSCs) are being developed rapidly and exhibit greatly potential commercialization. Herein, it is found that the device performance can be improved by manipulating the migration of iodine ions via reverse‐biasing, for example, at −0.4 V for 3 min in dark. Characterizations suggest that reverse bias can increase the charge recombination resistance, improve carrier transport, and enhance built‐in electric field. Iodine ions including iodine interstitials in perovskites are confirmed to migrate and accumulate at the SnO2/perovskite interface under reverse‐basing, which fill iodine vacancies at the interface and interact with SnO2. First‐principles calculations suggest that the SnO2/perovskite interface with less iodine vacancies has a stronger interaction and higher charge transfer, leading to larger built‐in electric field and improved charge transport. Iodine ions that may pass through the SnO2/perovskite interface are also confirmed to be able to interact with Sn4+ and passivate oxygen vacancies on the surface of SnO2. Consequently, an efficiency of 23.48% with the open‐circuit voltage (Voc) of 1.16 V is achieved for PSCs with reverse‐biasing, as compared with the initial efficiency of 22.13% with a Voc of 1.10 V. These results are of great significance to reveal the physics mechanism of PSCs under electric field.

Interfacial defects greatly influence the performance of perovskite solar cells (PSCs), and interface engineering is a powerful technique to promote the power conversion efficiency (PCE) of PSCs. Herein, an interfacial passivation strategy is developed employing cesium fluoride (CsF) to modify the surface of a perovskite film. Theoretical calculations suggest that the Cs+ and F− ions have a targeted passivation effect to decrease the defect density of the perovskite. Meanwhile, Cs+-formamidine+ (FA+) and F−–I− ion exchange can occur on the perovskite surface, which leads to the decline of the Fermi level of perovskite and reinforces the built-in potential of PSCs. Additionally, experiment results also confirm the reduction in the interfacial defects and the enhancement of the built-in potential. Consequently, the open-circuit voltage ( Voc) of PSCs is increased from 1.07 to 1.12 V, contributing to the promotion of the PCE. Furthermore, the stability of PSCs is obviously improved as well owing to the suppressed phase transition of α-phase perovskite. Our findings provide guidelines for surface modification of perovskite crystals to enhance the performance and stability of PSCs.