Additive Assisted Growth of Pb-Sn Mixed Low-bandgap Absorber for Efficient Perovskite Solar cells

Pb-Sn mixed low-bandgap perovskites suffer from the quick formation of surface defects and charge traps within the perovskite surface during film formation. Furthermore, the facile oxidation of Sn⁺² into more stable Sn⁺⁴ introduces Sn vacancies and point defects, introducing non-radiative recombination pathways. This would compromise the PV parameters of the final solar device. This work accurately tries to suppress the formation of perovskite surface defects and traps via additive-assisted growth of highly crystalline perovskite film by using a controlled amount of  Phenethylammonium Hydrochloride (PEACl), i.e.,  (C₈H₁₂ClN) to the Pb-Sn mixed perovskite solution. As a result, passivated FA_0.85 MA_0.1 Cs_0.05 Pb_0.5Sn_0.5I₃ films possess lower electronic disorder, as evidenced with Urbach energy calculation. Moreover, PEACl passivated perovskite films exhibit improved crystallinity, film morphology, and lower trap densities, as evidenced with XRD, SEM, and space charge limited current experiments. In addition, PEACl performs Sn-N coordination bonding with Sn²⁺ and reduces the Sn vacancies on the perovskite surface, which helps to improve the device performance. Consequently, the power conversion efficiency boosts from 14.11% to 17.21% through the simultaneous improvement of open-circuit voltage (V_OC) and fill factor (FF).