Surface Dedoping for Methylammonium-Free Tin–Lead Perovskite Solar Cells

Abstract

For Sn−Pb-based perovskite solar cells (PSCs), surface p-doping-related defects including Sn vacancies, FA vacancies, and I-related defects substantially impact the local work function and band structure, thus resulting in inefficient carrier transfer kinetics at the perovskite/C 60 interface. Herein, a surface dedoping strategy is rationally designed based on synergistic passivation of p-doping-related defects, in which shallow-level defects are compensated and localized electronic states caused by deep-level defects are removed. Accordingly, the back surface electrical-field by a concomitantly formed n/n + homojunction as well as reduced surface potential fluctuations minimize the electron extraction barrier. The electron mobility and built-in voltage are greatly enhanced, and carrier lifetimes are elongated to over 7 μs. Meanwhile, the cooperative stabilization of surface components suppresses I − ion migration and Sn 2+ oxidation. The resulting MA-free Sn−Pb PSCs deliver a champion efficiency of 22.05%, along with maintaining 94% of the initial efficiency after 1200 h of aging in N 2 .

Narrow Bandgap Metal Halide Perovskites for All-Perovskite Tandem Photovoltaics

“…The possible underlying mechanism of this doping/dedoping effect can be related to the factors that are responsible for the variation of the carrier concentrations . In this particular case, it might be caused by, for example, (i) the suppressed formation of defects raising the p-doping, tin vacancies and interstitial iodine defects, , owing to the enhanced lattice stability; (ii) the change of the perovskite surface composition to the state with an increased formation energy of the tin vacancies; , (iii) the change of the surface defect states being dominated by the donor-type shallow defects; , (iv) the change of the length of the metal−halide bond and/or the tilt of the MX 6 octahedral of the perovskite lattice, upon the binding of the ligands to the surface of the perovskite; and/or (v) the enhanced charge transfer doping from the next contact, i.e., ETL, in the stacked structure. ,, To the best of our knowledge, however, a comprehensive study is still lacking for mixed Sn−Pb perovskites in these aspects. Meanwhile, the cyclic diamines piperazine (PP), 4-aminopiperidine (4APP), and 4-(aminomethyl)­piperidine (4AMP) also lead to the formation of an n-type surface in mixed Sn−Pb perovskites .…”