Ethanol Processable Inorganic-Organic Hybrid Hole Transporting Layers Enabled 20.12 % Efficiency Organic Solar Cells

In this study, a high-performance inorganic-organic hybrid hole transporting layer (HTL) was developed using ethanol-soluble alkoxide precursors and a self-assembled monolayer (SAM). Three metal oxides-vanadium oxide (VO_x), niobium oxide (Nb₂O₅), and tantalum oxide (Ta₂O₅)-were synthesized through successive low-temperature (100 °C) thermal annealing (TA) and UV-ozone (UVO) treatments of their respective precursors: vanadium oxytriethoxide (EtO-V), niobium ethoxide (EtO-Nb), and tantalum ethoxide (EtO-Ta). Among these, the Nb₂O₅ film exhibited excellent transmittance, a high work function, and good conductivity, along with a more compact and uniform structure featuring fewer interfacial defects, which facilitated efficient charge extraction and transport. Furthermore, the deposition of a SAM of (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) on top of Nb₂O₅ further passivated defects, enhancing interfacial contact with the photoactive layer. The resulting inorganic-organic hybrid HTL of Nb₂O₅/2PACz demonstrated excellent compatibility with various photoactive blends, achieving impressive power conversion efficiencies of 19.44 %, 19.18 %, and 20.12 % for the PM6:L8-BO, PM6:BTP-eC9, and D18:BTP-eC9 based organic solar cells, respectively. 20.12 % is the best performance for bulk heterojunction organic solar cells with binary components as the photoactive layer.