Theoretical study on structural properties of silicon-doped benzothiazole/SnO2 (1 0 0): A novel molecular design for solar cells

Conjugated polymers have recently drawn interest owing to their high-power conversion efficiency in bulk heterojunction solar cells. Based on 4-(5-bromothiophen-2-yl)-7-(5-((4-nonyl-5-ethynylthiophen-2-yl) ethynyl)-thiophen-2-yl) benzothiadiazole (A4B7BT), organic polymer monomers for solar cells are designed, aided by silicon-doping, using density functional theory (DFT) at the GGA/PW91/DNP level. Comparison and screening of stable configuration, stable energy, and frontier orbital energy gap indicate that, A4B7BT-3Si is the best configuration when the positions of 1, 3, and 5 carbon atoms on the BT unit of A4B7BT are replaced by 3Si atoms simultaneously. To further explore the photovoltaic (PV) properties of silicon-doped A4B7BT, DFT and the periodic plane slab model are combined to investigate A4B7BT-xSi (x = 1–6) adsorbed on the SnO2 (1 0 0) surface. The stable structures, Mulliken charges, frontier orbitals, energy band structures, and density of states are discussed in detail. The results reveal that the energy gap (1.17 eV) in SnO2 (1 0 0)-A4B7BT-3Si is close to that of single-crystal Si. This study potentially guides the strategic development of future PV materials.