Investigating Dopant Effects in ZnO as an Electron Transport Layer for Enhanced Efficiency in Organic Photovoltaics

Abstract The power conversion efficiencies of organic solar cells greatly depend on the device architecture and choice of charge transporting materials. Improved power conversion efficiency (PCE) for inverted organic solar cells is observed when using Sn‐doped ZnO as the electron transporting layer. By doping the elements with different numbers of valence electrons (Al 3+ and Sn 4+ ions) into the ZnO matrix, device conversion efficiencies of 8.69% and 9.21%, respectively, are achieved. Conductive atomic force microscopy (CAFM) observations reveal that the Sn‐doped ZnO film exhibits better conductivity due to its larger number of carrier charges. X‐ray photoemission spectroscopy (XPS) indicates larger oxygen vacancies (OV) in Sn‐doped ZnO. Electrochemical characterization exhibits that there is a reduction in series resistance and charge transfer (CT) resistance for SZO, indicating the optimal charge transport capability of the electron transport layer (ETL). Ultrafast time‐resolved studies further show that, in comparison with Al‐doped ZnO and un‐doped ZnO, the elevated carrier concentration in Sn‐doped ZnO plays a significant role in augmenting the photocurrent. Thus, it is determined how dopants in ETL influence CT mechanisms, enhancing the photovoltaic conversion efficiency, thus contributing to the development of cost‐effective and efficient photovoltaic technologies.