Researchers at the Huaqiao University in China have fabricated a four-terminal (4T) perovskite-silicon solar cell with a top cell based on a perovskite material with an energy bandgap of 1.67 and lower surface defects.
The scientists utilized a surface reconstruction method to remove the surface defects from the wide-bandgap perovskite by wet nano-polishing. “We found that the surface reconstruction strategy can improve the contact of the perovskite/C60 interface, release the residual lattice strain of the bulk perovskite film, and form a bromine-rich perovskite surface layer, which effectively suppresses the interface carrier loss and the ion migration,” they explained,
The proposed technique was reportedly able to remove the defect-rich regions caused by inadequate crystallization on the perovskite film surface, as well as the soft iodine-rich halide components that can adjust the energy level matching. Nano-polishing was found to retrain the phase separation and suppress the crystallinity inhomogeneity of the film, which the academics said reduces the lattice mismatch between the surface and the bulk.
They also found that nano-polishing enhances the photoluminescence (PL) intensity of the perovskite film ensuring more uniform PL distribution. “Measurements indicated a notable reduction in the non-radiative carrier recombination in the perovskite films,” they added.
In the study “Surface reconstruction of wide-bandgap perovskites enables efficient perovskite/silicon tandem solar cells,” published in nature communications, the research group explained it built the 300 mm × 300 mm perovskite cell with a substrate made of glass and indium tin oxide (ITO), a hole transport layer (HTL) made of nickel(II) oxide (NiOx) and phosphonic acid called methyl-substituted carbazole (Me-4PACz), and a perovskite absorber.
The academics fabricated two different versions of this cell, one opaque and one semi-transparent, which achieved a power conversion efficiency of 23.67% and 21.70%, respectively. Furthermore, both devices were found to retain 80% of the initial efficiency after operation at the maximum power point under 1-sun illumination for 1,505 h.
The team utilized the semi-transparent cell to build a tandem cell integrating a 158.75 mm × 158.75 mm back contact (BC) silicon solar cell purchased from Gold Stone (Fujian) Energy Company Limited with an efficiency of 12.7% as a bottom device, with the large-area perovskite cell being placed on the top of the hybrid BC silicon solar cell as a filter.
Tested under standard illumination conditions, the tandem cell achieved a power conversion efficiency of 33.10%.
“This work reveals that the surface passivation of perovskite films with a high density of defects like wide-bandgap perovskite films requires a pre-step to reduce the defect density in the initial films, indicating directions for designing surface engineering strategies for further boosting the performance of wide-bandgap perovskite solar cells,” the scientists stated.
