The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in by up to 100 millivolts. We achieved a high of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

During the past 6 years, perovskite solar cells have experienced a rapid development and shown great potential as the next‐generation photovoltaics. For the perovskite solar cells with regular structure (n‐i‐p structure), device efficiency has reached over 20% after the intense efforts of researchers from all over the world. Recently, perovskite solar cells with the inverted structure (p‐i‐n structure) have been becoming more and more attractive, owing to their easy‐fabrication, cost‐effectiveness, and suppressed hysteresis characteristics. Some recent progress in their device performance and stability has indicated their promising future. Here, recent developments and future perspectives about inverted perovskite solar cells are reviewed. Interface engineering, film morphology control, device stability, hysteresis phenomena and other research hotspots are discussed to present the roadmap for the development of inverted perovskite solar cells.

The past 5 years have witnessed the rise of highly efficient organometal halide perovskite-based solar cells. In conventional perovskite solar cells, compact n-type metal oxide film is always required as a blocking layer on the transparent conducting oxide (TCO) substrate for efficient electron-selective contact. In this work, an interface engineering approach is demonstrated to avoid the deposition of compact n-type metal oxide blocking film. Alkali salt solution was used to modify the TCO surface to achieve the optimized interface energy level alignment, resulting in efficient electron-selective contact. A remarkable power conversion efficiency of 15.1% was achieved under AM 1.5 G 100 mW · cm(-2) irradiation without the use of compact n-type metal oxide blocking layers.

The charge-carrier balance strategy by interface engineering is employed to optimize the charge-carrier transport in inverted planar heterojunction perovskite solar cells. N,N-Dimethylformamide-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(methyl methacrylate)-modified PCBM are utilized as the hole and electron selective contacts, respectively, leading to a high power conversion efficiency of 18.72%

Organic-inorganic lead halide perovskites are emerging materials for the nextgeneration photovoltaics. Lead halides are the most commonly used lead precursors for perovskite active layers. Recently, lead acetate (Pb(Ac)2) has shown its superiority as the potential replacement for traditional lead halides. Here, we demonstrate a strategy to improve the efficiency for the perovskite solar cell based on lead acetate precursor. We utilized methylammonium bromide as an additive in the Pb(Ac)2 and methylammonium iodide precursor solution, resulting in uniform, compact and pinhole-free perovskite films. We 2 observed enhanced charge carrier extraction between the perovskite layer and charge collection layers and delivered a champion power conversion efficiency of 18.3% with a stabilized output efficiency of 17.6% at the maximum power point. The optimized devices also exhibited negligible current density-voltage (J-V) hysteresis under the scanning conditions.

The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium and formamidinium mixed cations. Currently, high-quality mixed-cation perovskite thin films are normally made by use of antisolvent protocols. However, the widely used "antisolvent"-assisted fabrication route suffers from challenges such as poor device reproducibility, toxic and hazardous organic solvent, and incompatibility with scalable fabrication process. Here, a simple dual-source precursor approach is developed to fabricate high-quality and mirror-like mixed-cation perovskite thin films without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible current density-voltage hysteresis. A stabilized power output approaching 20% is obtained at the maximum power point. These results shed light on fabricating highly efficient perovskite solar cells via a simple process, and pave the way for solar cell fabrication via scalable methods in the near future.

high performance in PHJ PSSCs, various approaches have been used, including interface engineering to optimize both the electron-and hole-selective contacts, [16][17][18][19] composition manipulation of the perovskite, [ 9,20,21 ] and morphology control of perovskite-active layers. [22][23][24] The goal of morphology control is to obtain compact, pin-hole free fi lms with large grain sizes, high purity, and better crystallinity, [ 23 ] which is usually achieved by tuning the annealing conditions to optimize growth of the perovskite crystal, [ 25,26 ] by incorporating additives in the precursor solution [ 27 ] or by using rapid deposition-crystallization procedures. [ 28 ] From these different studies, it is evident that optimizing the crystallization and grain growth condition is critical in achieving high quality fi lms to enhance device performance.The sequential deposition of the CH 3 NH 3 PbI 3 layer developed by Gratzel and co-workers has been recognized as an effective approach to control crystallization and grain growth of perovskite fi lms. [ 29 ] In the traditional sequential deposition process, PbI 2 is fi rst deposited onto mesoporous TiO 2 support layers. The CH 3 NH 3 I (MAI) solution is then exposed to PbI 2 to produce CH 3 NH 3 PbI 3 . The mesoporous TiO 2 support layer acts as a scaffold, transferring its morphology to PbI 2 , enabling the effi cient diffusion of CH 3 NH 3 I into PbI 2 , leading to a high conversion effi ciency of PbI 2 . However, in the planar heterojunction, the conversion of PbI 2 to CH 3 NH 3 PbI 3 can be less effi cient since the dense and compact PbI 2 fi lm retards the diffusion of MAI. [ 30 ] To address this challenge, various methods have been proposed. Vapor-assisted solution method, [ 31 ] solvent engineering of the PbI 2 solution, [ 32 ] and annealing-driven interdiffusion process [ 23 ] have been reported to achieve the complete reaction between PbI 2 and CH 3 NH 3 I, giving better quality of perovskite fi lms.Here, we take a new approach to develop mesoporous PbI 2 scaffolds, employing the nucleation and growth of PbI 2 crystallites in a wet fi lm. We demonstrate a facile time-dependent growth control that allows us to manipulate the mesoporous PbI 2 layer quality in a continuous fashion. We show that the morphology of PbI 2 infl uences the subsequent crystallization of CH 3 NH 3 PbI 3 fi lm by using angle-dependent grazing incidence X-ray scattering. The morphology of PbI 2 fi lm can be fi netuned, and thus the CH 3 NH 3 PbI 3 fi lm quality can be effectively controlled, leading to an optimization of the perovskite active layer. Using this strategy, PSSCs with inverted PHJ structure showed a PCE of 15.7% with little hysteresis. Figure 1 a shows the methodology of the time-dependent controlled growth of mesoporous PbI 2 fi lm. Briefl y, the solution of PbI 2 in N , N -dimethylformamide (DMF) was spin-coated onto the substrates under an N 2 atmosphere in a glovebox.Perovskite solar cells (PSSCs) are now a top candidate for highperformance and low-cost thin fi lm photo...

The δ → α phase transformation is a crucial step in the solution-growth process of formamidinium-based lead triiodide (FAPbI 3 ) hybrid organic−inorganic perovskite (HOIP) thin films for perovskite solar cells (PSCs). Because the addition of cesium (Cs) stabilizes the α phase of FAPbI 3based HOIPs, here our research focuses on FAPbI 3 (Cs) thin films. We show that having a large grain size in the δ-FAPbI 3 (Cs) non-perovskite intermediate films is essential for the growth of high-quality α-FAPbI 3 (Cs) HOIP thin films.Here grain coarsening and phase transformation occur simultaneously during the thermal annealing step. A large starting grain size in the δ-FAPbI 3 (Cs) thin films suppresses grain coarsening, precluding the formation of voids at the final α-FAPbI 3 (Cs)−substrate interfaces. PSCs based on the interface void-free α-FAPbI 3 (Cs) HOIP thin films are much more efficient and stable in the ambient atmosphere. This interesting finding inspired us to develop a simple room-temperature aging method for preparing coarse-grained δ-FAPbI 3 (Cs) intermediate films, which are subsequently converted to coarse-grained, high-quality α-FAPbI 3 (Cs) HOIP thin films. This study highlights the importance of microstructure meditation in the processing of formamidinium-based PSCs.