Protonation-associated regulation of buried PEDOT:PSS interfaces enables improved performance in inverted perovskite solar cells

Abstract

The buried poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/perovskite interface strongly influences inverted perovskite solar cells, whereas the acidic and hydrophilic PSS-rich surface can adversely affect perovskite film formation and interfacial stability. Here, an alcohol-assisted 4-tert-butylpyridine (tBP) post-treatment is used to regulate the buried interface before MAPbI3 deposition. Zeta-potential and Fourier-transform infrared measurements indicate pronounced tBP/PSS acid-base and ionic interactions, while x-ray photoelectron spectroscopy provides an independent surface-sensitive probe of the associated chemical-state and compositional changes. The fitted PSS/PEDOT S 2p area ratio decreases from approximately 8.07 for pristine PEDOT:PSS to 6.88 for tBP/isopropanol (IP)-treated PEDOT:PSS, and the N 1s spectra of the tBP-containing samples show treatment-dependent changes in the pyridinic-N environment. These interfacial changes are accompanied by improved perovskite film quality and a reduced space-charge-limited-current trap-filled-limit voltage, from 0.76 V for the untreated sample to 0.57 V for tBP/IP, corresponding to an approximately 25% reduction in the relative trap-density metric for comparable device geometry. The tBP/IP treatment gives the best photovoltaic performance, increasing the power conversion efficiency from 14.99% to 17.61% and retaining more than 95% of the initial efficiency after 450 h of unencapsulated ambient shelf storage.