| Summary: | Abstract Transparent electrodes (TEs) are vital in optoelectronic devices, enabling the interaction of light and charges. While indium tin oxide (ITO) has traditionally served as a benchmark TE, its high cost prompts the exploration of alternatives to optimize electrode characteristics and improve device efficiencies. Conducting polymers, which combine polymer advantages with metal‐like conductivity, emerge as a promising solution for TEs. This work introduces a two‐in‐one electron transport layer (ETL) and TE based on films of polyethylenimine ethoxylated (PEIE)‐modified poly(benzodifurandione) (PBFDO). These PEIE‐modified PBFDO layers exhibit a unique combination of properties, including low sheet resistance (130 Ω sq−1), low work function (4.2 eV), and high optical transparency (>85% in the UV–vis‐NIR range). In contrast to commonly used poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the doping level of PBFDO remains unaffected by the PEIE treatment, as verified through UV–vis‐NIR absorption and X‐ray photoelectron spectroscopy measurements. When employed as a two‐in‐one ETL/TE in organic solar cells, the PEIE‐modified PBFDO electrode exhibits performance comparable to conventional ITO electrodes. Moreover, this work demonstrates all‐organic solar cells with record‐high power conversion efficiencies of >15.1% under indoor lighting conditions. These findings hold promise for the development of fully printed, all‐organic optoelectronic devices.
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