Methylammonium-free, high-performance, and stable perovskite solar cells on a planar architecture

TLDR

High‑performance perovskite solar cells traditionally rely on bromine and the thermally unstable methylammonium, limiting bandgap optimization and stability. This work pursues a methylammonium‑free approach to create inherently stable perovskites compatible with tandem and flexible‑substrate applications. By tuning inorganic cations with rubidium and cesium, the authors fabricated highly crystalline, Br‑ and MA‑free formamidinium perovskites that, in a planar device with polymeric interlayers, achieved a stabilized 20.35 % efficiency—among the highest for MA‑free cells—and demonstrated markedly improved stability without heating beyond 100 °C.

Abstract

Currently, perovskite solar cells (PSCs) with high performances greater than 20% contain bromine (Br), causing a suboptimal bandgap, and the thermally unstable methylammonium (MA) molecule. Avoiding Br and especially MA can therefore result in more optimal bandgaps and stable perovskites. We show that inorganic cation tuning, using rubidium and cesium, enables highly crystalline formamidinium-based perovskites without Br or MA. On a conventional, planar device architecture, using polymeric interlayers at the electron- and hole-transporting interface, we demonstrate an efficiency of 20.35% (stabilized), one of the highest for MA-free perovskites, with a drastically improved stability reached without the stabilizing influence of mesoporous interlayers. The perovskite is not heated beyond 100°C. Going MA-free is a new direction for perovskites that are inherently stable and compatible with tandems or flexible substrates, which are the main routes commercializing PSCs.