Constructing orderly crystal orientation with a bidirectional coordinator for high efficiency and stable perovskite solar cells

Abstract

A well-developed perovskite crystal at the beginning of a crystal lattice facilitates favourable growth orientation for efficient charge transport and the elimination of buried interfaces. However, rapid and uncontrollable crystallization of perovskites poses significant challenges in achieving desired growth orientations and controlling the growth direction during crystallization, necessitating the establishment of optimal substrate conditions. In this study, we propose a bidirectional coordination strategy involving the introduction of cesium trifluoroacetate (CsTFA) onto a tin dioxide (SnO₂) surface. Treatment with CsTFA facilitates the passivation of SnO₂ vacancies via COOH–Sn while concurrently forming intermolecular interactions with overlying perovskite crystals, manifested as CF₃⋯H–N for formamidinium (FA⁺) and CF₃⋯I–Pb, respectively. These interactions initiate the well-established beginning of the perovskite crystals and promote their vertical growth. Consequently, vertically grown perovskite crystals exhibit reduced tensile strain and fewer crystalline defects. Furthermore, a benign buried interface between the perovskite and underlying SnO₂ mitigates detrimental damage, thereby suppressing non-radiative recombination losses. This synergetic bidirectional coordination contributes to the fabrication of perovskite solar cells with a maximum power conversion efficiency of 25.60% (certified at 25.39%) and long-term stability under light illumination.