PTB7-Th based organic solar cell with a high Voc of 1.05 V by modulating the LUMO energy level of benzotriazole-containing non-fullerene acceptor

Abstract

The open-circuit voltage (Voc) of classical photovoltaic polymers, such as P3HT and PTB7-Th, are always restricted when combining with fullerene derivatives, due to the difficulty of modulating the energy levels of fullerene derivatives. Thus, design of new non-fullerene small molecule acceptor (NFSMA) is very significant to match with these mature polymer donors and improve the Voc and power conversion efficiency (PCE). Here, a new benzotriazole (BTA)-based NFSMA, BTA7 was synthesized by adopting A2A1DA1A2 type molecular backbone. By using a strong electron-accepting unit of malononitrile (M) as terminal segment A2, BTA7 demonstrates strong crystallinity, red-shifted absorption spectrum and down-shifted lowest unoccupied molecular orbital (LUMO) energy levels in comparison with BTA1 and BTA2. Organic solar cells (OSCs) based on PTB7-Th:BTA7 realized a high Voc of 1.05V with a moderate PCE of 4.60%. The energy loss (Eloss=Eg−eVoc) of 0.53eV is lower than the experiential minimum value of 0.6eV, which indicates PTB7-Th still has large potential to improve the Voc and photovoltaic performance after the development of novel electron acceptors.