Concurrent cationic and anionic perovskite defect passivation enables 27.4% perovskite/silicon tandems with suppression of halide segregation

Abstract

Context & scale Wide-band-gap perovskite solar cells are considered attractive options to build tandem solar cells, combined with well-established silicon bottom cells. However, wide-band-gap perovskites, obtained through partially substituting iodine for bromine in the crystal lattice, suffer from light-induced phase segregation. In addition, perovskites, because of their ionic nature, feature various defect states, which hampers device performance. To address these issues simultaneously, we report a concurrent cationic and anionic perovskite defect passivation strategy using the phenformin hydrochloride molecule, containing both electron-rich and electron-poor functional groups. The concurrent passivation of the perovskite defects suppresses phase segregation of wide-band-gap perovskites and improves performance of monolithic perovskite/silicon tandem solar cells. Consequently, our findings provide critical insights for improved passivation of perovskites and the fabrication of wide-band-gap perovskite-based solar cells. Highlights •Phenformin HCl molecule concurrently passivates cationic and anionic perovskite defects •The concurrent passivation suppresses phase segregation of wide-band-gap perovskites •Phenformin HCl passivation improves the performance of perovskite solar cells •The passivated perovskite/silicon tandem solar cells deliver efficiencies up to 27.4% Summary Stable and efficient perovskite/silicon tandem solar cells require defect passivation and suppression of light-induced phase segregation of the wide-band-gap perovskite. Here, we report how molecules containing both electron-rich and electron-poor moieties, such as phenformin hydrochloride (PhenHCl), can satisfy both requirements, independent of the perovskite’s surface chemical composition and its grain boundaries and interfaces. PhenHCl-passivated wide-band-gap (∼1.68 eV) perovskite p-i-n single-junction solar cells deliver an open-circuit voltage (VOC) ∼100 mV higher than control devices, resulting in power conversion efficiencies (PCEs) up to 20.5%. These devices do not show any VOC losses after more than 3,000 h of thermal stress at 85°C in a nitrogen ambient. Moreover, PhenHCl passivation improves the PCE of textured perovskite/silicon tandem solar cells from 25.4% to 27.4%. Our findings provide critical insights for improved passivation of metal halide perovskite surfaces and the fabrication of highly efficient and stable perovskite-based single-junction and tandem solar cells.

Keywords Perovskite, Solar cells, Tandems, Passivation, Silicon