Molecular design of donor-acceptor conjugated copolymers based on C-, Si- and N-bridged dithiophene and thienopyrroledione derivatives units for organic solar cells

摘要

The aim of this work is to adjust the electron-withdrawing strength in donor-acceptor (D-A) conjugated polymers for the improvements of photovoltaic performances. To achieve this goal, starting from the reported a series of D-A copolymers(PCPDTTPD(Pa1), PDTSTPD (Pa2) and PDTPTPD (Pa3)) based on electron-rich C-, Si-, N-bridged bithiophene and electron-deficient thienopyrroledione (TPD), we replace nitrogen atoms with sulfur or oxygen atoms on TPD unit to form two types of new D-A copolymers (Pb1 -Pb3 and Pc1-Pc3). Compared with Pa1-Pa3, the designed copolymers of Pb1-Pb3 and Pc1-Pc3 show better performances with smaller band gaps, lower HOMO energy levels, wider optical absorption, larger open circuit voltage (V_(oc)), and larger hole mobility. The power conversion efficiencies (PCEs) of ～8.8%, ～ 10.0%, ～8.4%, ～8.5%, ～9.9% and ～7.9% for organic solar cell made from designed polymers (Pb1, Pb2, Pb3, Pc1, Pc2, Pc3) are predicted by Scharber models. Conclusively, we conclude that the introduction of the strong electron-withdrawing groups into copolymer can effectively improve the electronic properties of the polymer in order to better the performance of organic solar cells.