Electron-transport-layer-free two-dimensional perovskite solar cells based on a flexible poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) cathode

Abstract

Recently, Ruddlesden–Popper two-dimensional (2D) perovskite solar cells (PSCs) have been intensively studied, owing to their high power conversion efficiency (PCE) and excellent long-term stability. In this work, we fabricated electron-transport-layer-free 2D PSCs using modified poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as an organic cathode. After treatment with phosphoric acid, the sheet resistance of the PEDOT:PSS electrode was significantly reduced from 1095 to 82 Ω sq⁻¹. After coating with polyethylenimine (PEIE), the work function of PEDOT:PSS can be tuned from −5.08 to −4.02 eV, which is suitable for electron extraction from a perovskite film. As a result, the complex preparation of TiO₂ can be skipped, which significantly lowers the total processing temperature of the PSCs to 120 °C. PEDOT:PSS/PEIE-based 2D PSCs on glass substrates exhibit a PCE of 10.2% (under forward scan), which is comparable to that of TiO₂-based conventional PSCs. However, the stability of the PSCs fabricated using PEDOT:PSS/PEIE as the cathode becomes better, with PCE degradation suppressed from 31.3% to 15.7% after a duration of 15 days. The flexible 2D PSCs on polyethylene naphthalate substrates exhibited a PCE of 8.5% with good bendability. Our results indicate that PEDOT:PSS/PEIE is a promising cathode material for fabricating efficient, flexible and stable 2D PSCs.