Stabilization of Highly Efficient and Stable Phase‐Pure FAPbI₃ Perovskite Solar Cells by Molecularly Tailored 2D‐Overlayers

Abstract

As a result of their attractive optoelectronic properties, metal halide APbI3 perovskites employing formamidinium (FA+) as the A cation are the focus of research. The superior chemical and thermal stability of FA+ cations makes α‐FAPbI3 more suitable for solar‐cell applications than methylammonium lead iodide (MAPbI3). However, its spontaneous conversion into the yellow non‐perovskite phase (δ‐FAPbI3) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired α‐FAPbI3 perovskite phase by protecting it with a two‐dimensional (2D) IBA2FAPb2I7 (IBA=iso‐butylammonium overlayer, formed via stepwise annealing. The α‐FAPbI3/IBA2FAPb2I7 based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. In addition, it showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress, that is, simultaneous exposure with maximum power tracking to full simulated sunlight at 80 °C over 500 h.

Moisture‐Resistant FAPbI3 Perovskite Solar Cell with 22.25 % Power Conversion Efficiency through Pentafluorobenzyl Phosphonic Acid Passivation

“…After cooling down to 150 °C, all substrates were transferred to a nitrogen‐filled glovebox for perovskite deposition. For the perovskite layer, FAPbI 3 perovskite precursor solution, in the presence of MACl as a crystallization aid, was prepared according to our previously reported method, [2b] by dissolving an equimolar mixture of PbI 2 and FAI with MACl in mixed solution of DMF/DMSO (4 : 1 v/v) under mild heating at about 70 °C to assist dissolution. The spinning procedure was carried out in a two‐step program at 1000 rpm for 10 s and 4000 rpm for 20 s. CB (200 μL) as antisolvent was added 10 s before the end of the last step.…”

Formamide iodide: a new cation additive for inhibiting δ-phase formation of formamidinium lead iodide perovskite

“…21 Nowadays, phase pure α-FAPbI3 films have achieved by several strategies such as using pre-synthesized FAPbI3 powder as precursor 22 or adding additives in the precursor solution. 23 To the best of our knowledge, highest PCE of 25.17% has achieved with FAPbI3 employing little amount of methylenediammonium dichloride and CsI as the additive. 3 Cation also affects the structure of perovskite compounds.…”

Recent Advances and Perspectives on Powder‐Based Halide Perovskite Film Processing

“…Therefore, stabilizing them in their desired perovskite α-phase, where FAPbI 3 exhibits an even better-suited bandgap energy compared to MAPbI 3 , is an important current research goal in the perovskite solar cell field. [43] In this context, mechanochemically synthesized CsPbI 3 and FAPbI 3 powders were found to directly crystallize in the black cubic α-phase and the degradation to the δ-phase is significantly slower than in corresponding thin films, processed via solvent-based approaches. [16,20] An overall high stability of mechanochemically synthesized perovskite powders has been repeatedly reported in literature.…”