Controlled pH of PEDOT:PSS for Reproducible Efficiency in Inverted Perovskite Solar Cells: Independent of Active Area and Humidity

Abstract

Perovskite solar cells (PSCs) show great promise, but the acidity of the hole transport layer (HTL) often leads to poor perovskite crystallinity, which limits their performance and introduces inconsistency into the measurement of device parameters. In this research, inverted MAPbI 3 perovskite photovoltaics are fabricated using a pH-controlled HTL. The pH of the PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) HTL is adjusted using imidazole, and devices with acid, neutral, and base pH HTLs are compared. The neutral HTL device exhibits improved nonwettability of the HTL surface, reduced perovskite roughness, and MAPbI 3 passivation, which improve the perovskite crystallinity. The neutral HTL improves the power conversion efficiency from 12.58% to 14.25% with an active area of 11.8 mm 2 by improving the external and internal quantum efficiency and inducing excellent charge generation and extraction. Additionally, enhanced performance is also observed using active areas of 6.9 and 15.0 mm 2 . The neutral-HTL-based device exhibits very consistent performance for various active area sizes, as the uniformity of the perovskite crystals minimizes dependence on the photon absorption area. The enhanced stability of the pH-controlled HTL-based PSCs, including preventing degradation by strong acid because of its reduced acidity, allows the device to retain its power conversion efficiency (PCE) value by maintaining its fill factor even at 80% humidity. © 2019 American Chemical Society.