Optimizing Solar Cell Performance: Hybrid Planar‐Si/Organic Heterojunction Solar Cells Achieve 14.75% Efficiency Through Dibenzothiophene‐Spirobifluorene‐Dithienothiophene Insertion Layer Integration

Hybrid planar‐Si/organic heterojunction solar cells have garnered substantial interest due to their potential for producing cost‐effective, high‐efficiency devices. This study investigates the photophysical properties and application of dibenzothiophene‐spirobifluorene‐dithienothiophene (DBBT‐mCbz‐DBT) in enhancing the efficiency of photovoltaic devices. Utilizing ultraviolet–visible and fluorescence spectroscopy, DBBT‐mCbz‐DBT is analyzed in solutions and doped films, showing maximum absorption at 380 nm and emission at 440 nm. Notably, the photoluminescence intensity in 4,4′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl films peaks at 40–50% DBBT‐mCbz‐DBT concentrations, which are selected for solar cell fabrication. Enhanced light absorption and charge transport are observed with a DBBT‐mCbz‐DBT layer on silicon, significantly improving device performance. The planar silicon/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (Si/PEDOT:PSS) heterojunction solar cells with DBBT‐mCbz‐DBT exhibit a power conversion efficiency of 14.75%, demonstrating substantial gains over baseline structures. The DBBT‐mCbz‐DBT layer optimizes energy band alignment, reduces recombination losses, and enhances electron transport, improving overall device efficiency. This research underscores the potential of integrating DBBT‐mCbz‐DBT in solar cells to achieve higher performance through simple, scalable fabrication methods.