Squaraine dyes containing diphenylamine group: Effects of different type structures on material properties and organic photovoltaic performances

摘要

Four donor-acceptor-donor (D-A-D') unsymmetrical squaraines (USQs) with different molecular skeletons (XZ-type and YZ-type), containing diphenylamine group with/without methoxy substituent were synthesized as donor materials in bulk-heterojunction (BHJ) organic photovoltaics (OPVs). The introduction of methoxy group in USQs has little different effects on the overall photovoltaic performance. Conversely, the different molecular skeleton types of the USQs have significant influence on their material properties and photovoltaic performances. Compared to BIDPSQ and BIDPOMeSQ with XZ-type molecular skeleton, IDPSQ and IDPOMeSQ with YZ-type molecular skeleton display closer solid-state packing, much lower highest occupied molecular orbital (HOMO) energy level, higher hole mobility and smaller phase separation domain size. Consequently, YZ-type USQs exhibit the most excellent performance with power conversion efficiency (PCE) of similar to 4%, which is approximately 300% higher than those of XZ-type USQs. Surprisingly, even though IDPSQ and IDPOMeSQ show wide band gaps, the corresponding devices still achieve a highest PCE of similar to 4%, which is comparable to or even higher than the PCEs of some reported SQ-based devices with low band gaps. These results indicate the YZ-type molecular skeleton and the electron-donating diphenylamine group are very promising to construct highly efficient squaraine donor materials.