Interface Engineering with Formamidinium Salts for Improving Ambient-Processed Inverted CsPbI₃ Photovoltaic Performance: Intermediate- vs Post-Treatment

Abstract

Inverted all-inorganic perovskite solar cells (PSCs) have attracted increasing attention owing to excellent thermal stability, easy fabrication, and adaptable application as top cell in tandem solar cells. Apart from efficiency, ambient processing is desirable for practical production. To avoid water invasion in ambient air, surface engineering for perovskites is reported as a valid approach. However, most were performed by post-treatment, which hardly regulates the formation process of perovskite crystals. This work demonstrates a simple but effective surface intermediate-treatment strategy to stabilize CsPbI3 perovskites fabricated in ambient air and compares the different effects yielded on the inverted PSCs. By using formamidinium (FA) salts for intermediate-treatment, the strong interaction between FA cation and [PbI6]4– octahedron improves the moisture resistance, and compared with the post-treatment strategy, the accelerated crystallization rate and the shortened exposure time to moisture reduce the devastation by water during film fabrication process further. Moreover, the greatly passivated defects and optimized energy level matching between perovskite and PCBM suppress the nonradiative recombination. Resultantly, the optimized device shows enhanced efficiency from 11.39% to 15.45%, and long-term stability is improved, with 97.6% efficiency remaining after storage for 1600 h. Therefore, we believe that this work can provide a promising guideline for fabricating all-inorganic inverted PSCs in a low-cost manufacturing scheme.

Challenges and modification strategies of air-processed all-inorganic CsPbX3 perovskite films for efficient photovoltaics

“…In addition to molecular passivation at the film surface, Fu et al reported that the 1,4-butanediamine (DAB) modification could polish the intrinsically formed lead-poor surface and eliminate the nonstoichiometric components [Figure 7C] [56] . Therefore, the deep-energy-level p-type traps are reduced, improving charge transfer at the CsPbI 3 /PCBM interface.…”

“…(C) X-ray photoelectron spectroscopy results at the surface and 10 nm depth and schematic diagram of the electron-transport dynamics based on the reference and polished films. Copyright from Ref [56] .…”

Simultaneous Defect Passivation and Electric Level Regulation with Rubidium Fluoride for High-Efficiency CsPbI2Br Perovskite Solar Cells

“…Organic–inorganic hybrid perovskite solar cells (PSCs) have already obtained extensive attention on account of their excellent optoelectronic properties. − So far, the power conversion efficiency (PCE) of organic–inorganic hybrid PSCs has rapidly surpassed 26% . However, their commercial applications are unfortunately restricted due to the volatilization and hydrophilicity of organic cations (MA + , FA + ). , Therefore, an all-inorganic CsPbX 3 (X = I, Br, Cl) perovskite has been synthesized by substituting the organic cations with inorganic Cs + . − Among the CsPbX 3 group, CsPbBr 3 is well-known for the best stability, but the largest bandgap (∼2.3 eV) limits its photovoltaic performance. , In contrast, α-phase CsPbI 3 possesses the narrowest bandgap (∼1.7 eV), but it can spontaneously transform to the optically inactive δ-phase in the ambient environment, dramatically hindering its practical applications. , By regulation of the ratio of halogen atoms, the mixed-halide CsPbI 2 Br all-inorganic PSC with a PCE of 9.8% was established in 2016 for the first time . CsPbI 2 Br perovskite displays a narrower bandgap (∼1.9 eV) than CsPbBr 3 and a more excellent phase stability than CsPbI 3 even in the ambient atmosphere, making it possible for serving as an appropriate top cell in tandem solar cells .…”