Unraveling Bulk versus Surface Passivation Effects in Highly Efficient p-i-n Perovskite Solar Cells Using Thiophene-Based Cations

Defect passivation is nowadays considered a must-have route for high-efficiency perovskite solar cells. However, a general rule that correlates the choice of passivating agents with performance enhancements is still missing. This work compares two different thiophene salts used as passivating agents, namely thiophene methylammonium chloride (TMACl) and thiophene ethylammonium chloride (TEACl), used for the passivation of bulk and surface defects in triple-cation (CsFAMA) based metal halide perovskites. First, we observe that the surface passivation method leads to better device performances reaching a power conversion efficiency of 23.56%, with reduced voltage losses and increased fill factor when compared to the reference. Second, we demonstrate that the chemical structure of the cation dictates its capability either in passivating bulk defects effectively or to form a superficial 2D/3D heterostructure, which happens only for the TEACl case. The chemical composition and the cation dimension are responsible for device performance enhancement as observed by a joint spectroscopic and density functional theory simulations study, providing rational guidelines for further smart device design.This article is protected by copyright. All rights reserved.

G.P., R.M., and A.Z. contributed equally to this work. A.Z., R.M., G.P., F.F., L.P., M.D.B., and G.G. acknowledge Edison for the collaboration, the project for infrastructures funded by Regione Lombardia RL3776. A.Z. and G.G. acknowledge the “HY-NANO” project that received funding from the European Research Council (ERC) Starting Grant 2018 under the European Union's Horizon 2020 research and innovation program (Grant Agreement no. 802862. A.Z., R.M., G.P., F.F., L.P., V.P., M.D.B., F.D., and G.G. acknowledge the Ministero dell’Università e della Ricerca (MUR) and the University of Pavia through the program “Dipartimenti di Eccellenza 2023–2027”. G.G., M.D.B., and G.P. acknowledge FARE (Framework per l’Attrazione e il Rafforzamento delle Eccellenze per la ricerca in Italia) Project EXPRESS (Exploring photoferroelectricity in halide perovskites for optoelectronics). R.M. and G.G. acknowledge the PhD Fellowship from Eni S.p.A. N.M and P.S. acknowledge the support by Slovak Research and Development Agency (APVV-20-0111, APVV-21-0297, SK-CZ-RD-21-0043, SK-AT-20-0006) and V4-Japan/JRP/2021/96/PeDET project.


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