The structural properties of silicon-doped DBrTBT/ZnSe solar cell materials: a theoretical study

Based on 4,7-di(5-bromothiophen-2-yl)-2,1,3-benzothiadiazole (DBrTBT), novel solar cell materials are designed via silicon-doping with the help of density functional theory (DFT) calculations at the GGA/PW91/DNP level. Comparison and selection of stable configurations, stable energy, and frontier orbital energy gaps indicate that DBrTBT-Si(1) is the optimal configuration when the C(1) atoms on the benzene ring of DBrTBT are replaced by Si atoms. To further explore the photovoltaic properties of DBrTBT-Si(1), DFT calculations of the periodic plane slab model are used to investigate DBrTBT and DBrTBT-Si(1) adsorbed on ZnSe(100) and ZnSe(111) surfaces, respectively. The stable structures, Mulliken charges, frontier orbitals, and density of states are further discussed in detail. The results indicate that the band gap between valence band and conduction band becomes wider when DBrTBT-Si(1) is adsorbed on the ZnSe(111) surface, and the Eg (1.31 eV) of the ZnSe(111)-DBrTBT-Si(1) is close to that of the single-crystal Si. This study potentially guides the development of future photovoltaic materials.