Flexible perovskite solar cells (f‐PSCs) have attracted great attention because of their unique advantages in lightweight and portable electronics applications. However, their efficiencies are far inferior to those of their rigid counterparts. Herein, a novel histamine diiodate (HADI) is designed based on theoretical study to modify the SnO2/perovskite interface. Systematic experimental results reveal that the HADI serves effectively as a multifunctional agent mainly in three aspects: 1) surface modification to realign the SnO2 conduction band upward to improve interfacial charge extraction; 2) passivating the buried perovskite surface, and 3) bridging between the SnO2 and perovskite layers for effective charge transfer. Consequently, the rigid MA‐free PSCs based on the HADI‐SnO2 electron transport layer (ETL) display not only a high champion power conversion efficiency (PCE) of 24.79% and open‐circuit voltage (VOC) of 1.20 V but also outstanding stability as demonstrated by the PSCs preserving 91% of their initial efficiencies after being exposed to ambient atmosphere for 1200 h without any encapsulation. Furthermore, the solution‐processed HADI‐SnO2 ETL formed at low temperature (100 °C) is utilized in f‐PSCs that achieve a PCE as high as 22.44%, the highest reported PCE for f‐PSCs to date.
Organic−inorganic Pb-based halide perovskite photoelectrical materials, especially perovskite solar cells (PSCs), have attracted attention due to the significant efforts in improving the power conversion efficiency (PCE) to above 25%. However, the stability issue of the PSCs restricts their further development for commercialization. Strategies are designed to keep moisture and oxygen out of the perovskite films, such as additive, surface passivation, and solvent engineering; however, usually, the corrosion of active films by the residual solvent is mostly ignored. Solvent residue is the paramount factor influencing the stability of the perovskite film prepared by the solution method, and most solvents can be easily absorbed and accelerate the perovskite film decomposition. Here, we studied the residual solvent effect on two kinds of perovskite films obtained by different annealing processes: hot air annealing and hot bench annealing. Several detection techniques were used to study the performance of two different annealing methods, including time-of-flight secondary ion mass spectrometry (ToF-SIMS), thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FESEM). The perovskite film obtained by hot air annealing shows less residual solvent and better device performance than the hot bench annealing method. This method is expected to provide insight into reducing solvent residue to improve the stability of the PSCs, especially for future commercialization.
Perovskite films prepared using the low-temperature solution method show plentiful defects, especially at grain boundaries and on the surface. A few additives have been exploited to fabricate high-quality perovskite films made up of larger grains with smaller boundaries and surfaces, and hence fewer defects, by slowing down the crystallization process. However, when the grain size becomes too large, the uniformity of the perovskite film is compromised. Herein, an additive, 1-hexanethiol (HA), is developed not only to appropriately enlarge grain size but also to form uniform perovskite films; meanwhile, most bulk defects are effectively passivated, leading to improved perovskite solar cell performance. As predicted by the density functional theory, the HA effectively forms a complex with the PbI2 in the precursor solution, which slowly releases free Pb2+ for controlled crystallization to form optimized perovskite film. The photoluminescence and trap density measurements demonstrate that the defects within perovskite film are significantly reduced owing to fewer grain boundaries, better crystallinity, and more effective passivation by HA. As a result, the efficiency of devices reaches 22.43% with negligible hysteresis. The unencapsulation device retains about 90% of its initial value when exposed to the ambient for 90 days, demonstrating its good stability. This development paves an effective avenue toward high-quality perovskite films for general optoelectronic applications, in particular for high-efficiency solar cells.
An efficient and stable inverted planar PSC with V2Ox additives is prepared in ambient air.
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