Composition Stoichiometry of Cs₂AgBiBr₆ Films for Highly Efficient Lead-Free Perovskite Solar Cells

Addressing the toxicity issue in lead-based perovskite compounds by seeking other nontoxic candidate elements represents a promising direction to fabricate lead-free perovskite solar cells. Recently, Cs2AgBiBr6 double perovskite achieved by replacing two Pb2+ with Ag+ and Bi3+ in the crystal lattice has drawn much attention owing to the convenient substitution of its chemical compositions. Herein, the dependence of the optoelectronic properties and corresponding photovoltaic performance of Cs2AgBiBr6 thin films on the deposition methods of vacuum sublimation and solution processing is investigated. Compared to the vacuum sublimation based one, the solution-processed Cs2AgBiBr6 shows inherently higher crystallinity, narrower electronic bandgap, longer photoexcitation lifetime, and higher mobility. The excellent optoelectronic properties are attributed to the accurate composition stoichiometry of Cs2AgBiBr6 films based on solution processing. These merits enable the corresponding perovskite solar cells to deliver a champion power conversion efficiency (PCE) of 2.51%, which is the highest PCE in the Cs2AgBiBr6-based double perovskite solar cells to date. The finding in this work provides a clear clue that a precise composition stoichiometry could guarantee the formation of high quality multicomponent perovskite films