In the current work, a series of bithiopheneimide (BTI)-based D-A copolymers were investigated based on the reported PDTSBTI (1) to screen excellent molecules toward organic photovoltaic (OPV) donor materials. It is found that the PCE based on the proposed derivative 4, where the silicon atom is replaced with vinyl and cyano groups on the DTS unit, shows a 70 percent improvement by Scharber diagrams compared with its prototype 1. Then, the charge transfer dynamics of 1/PC71BM and 4/PC71BM were investigated, including the intermolecular charge transfer (inter-CT) and recombination (inter-CR) rates. The theoretical data demonstrate that the ratio kinter-CT/kinter-CR of 4/PC71BM heterojunction is about 1 × 10(5) times higher than that of 1/PC71BM. These results clearly reveal that the designed donor molecule 4 will be a promising candidate for high-performance OPV device. We expect that this work from electron processing at the D/A interface may provide a theoretical guideline for further optimization and design of organic copolymer donor materials.

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Ten porphyrin sensitizers with different electron-withdrawing groups derived from the best sensitizer SM315 were investigated by means of the density functional theory (DFT) and time-dependent DFT calculations. To this end, major factors affecting the performance of the cell, including light harvesting, electron injection, dye regeneration, and conduction band energy shift are taken into consideration. Especially, the calculated distance (r) from the electron recapture center to the semiconductor surface is used to probe the charge recombination process. In addition, considering the complexity of the porphyrin sensitizers' absorption, the maximum short circuit current density (J(max)sc) is determined for investigating the light harvesting ability quantitatively. We find that when compared to SM315 with 2,1,3-benzothiadiazole, 1 with naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole shows better performance due to both larger J(max)sc and r, and 7 with diketopyrrolopyrrole could also be a promising candidate due to the much larger J(max)sc and comparable r.