Researchers from China's Huazhong University of Science and Technology, Wuhan University of Technology and Huaneng Clean Energy Research Institute have reported a surface reconstruction strategy utilizing a surface polishing agent, 1,4-butanediamine, together with a surface passivator, ethylenediammonium diiodide, to eliminate Sn-related defects and passivate organic cation and halide vacancy defects on the surface of Sn–Pb mixed perovskite films.
The team explained that while all-perovskite tandem solar cells have shown great promise in breaking the Shockley–Queisser limit of single-junction solar cell, their efficiency is often hindered by the surface defects induced non-radiative recombination loss in Sn–Pb mixed narrow bandgap perovskite films. The strategy detailed in their recent work not only delivers high-quality Sn–Pb mixed perovskite films with a close-to-ideal stoichiometric ratio surface, but also minimizes the non-radiative energy loss at the perovskite/electron transport layer interface.
The group designed a 0.0871 cm2 cell with the treated Sn-Pb perovskite absorber, an electron transport layer (ETL) based on buckminsterfullerene (C60), a hole transport layer (HTL) based on PEDOT-PSS, and a gold (Au) metal contact. Their Sn–Pb mixed perovskite solar cells with bandgaps of 1.32 and 1.25 eV realized power conversion efficiencies of 22.65% and 23.32%, respectively.
The best-performing BDA-EDAI2 modified device achieved a power conversion efficiency of 28.80%, an open-circuit voltage of 2.13 V (2.13 V), a short-circuit current density of 16.06 mA cm−2, and a fill factor of 84.19%. “We also verified the effectiveness of the surface reconstruction in module-level devices and obtained a champion PCE of 23.39% with an aperture area of 11.3 cm2,” the academics stated.
Furthermore, they found that the encapsulated tandem cells retained 79.7% of their initial efficiency after continuous operation under maximum power point tracking (MPPT) in ambient air for 550 h.
An unspecified third-party organization also certified that the best-performing devices achieved an efficiency of 28.49%, which the research group described as one of the highest efficiencies ever reported for all-perovskite solar cells.
