Dihydropyrazine-reductant effects on band bending at PEDOT:PSS/perovskite interfaces in tin halide perovskite solar cells

Abstract

This study investigates the effects of reducing treatment by 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine (TM-DHP) additives on band bending in the perovskite surface near poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole-selective contacts in tin-based-perovskite solar cells. We took electron spin resonance (ESR) spectroscopy measurements of PEDOT:PSS/tin perovskite stacks in the dark and under one-sun illumination. The findings indicate that downward band bending is formed in the tin perovskite layer near the PEDOT:PSS layer. This downward bending is not favorable in terms of surface passivation and hole selectivity. On the other hand, upward band bending occurs in stacks including tin perovskite layers with TM-DHP additives, indicating that TM-DHP prevents oxidation of tin perovskite, thus unfavorable downward band bending. ESR measurements of PEDOT:PSS/tin perovskite stacks without TM-DHP under illumination suggest reduction in the number of polarons caused by electron transport from perovskite layers toward PEDOT:PSS, which is driven by the unfavorable downward band bending. However, such electron transport toward PEDOT:PSS is prevented in PEDOT:PSS/tin perovskite stacks with TM-DHP. These findings, which demonstrate TM-DHP effects on interface band bending, are important for realizing highly efficient and stable tin perovskite solar cells.