Enhancing Photoinduced Charge Separation through Donor Moiety in Donor-Acceptor Organic Semiconductors

Three systems were designed, synthesized, and characterized to understand decay processes of photoinduced charge separation in organic semiconductors that are imperative for efficient solar energy conversion. A styrene-based indoline derivative (YD) was used as donor moiety (D), a triazine derivative (TRC) as the first acceptor (A(1)), and 9,10-anthraquinone (AEAQ) as a second acceptor (A(2)) in constructing two systems, YD-TRC and YD-TRC-AEAQ, The lifetime of the photoinduced charge-separated states in YD-TRC, a D-A(1) system, was found to be 215 ns and that in YD-TRC-AEAQ, a D-A(1)-A(2) system, to be 1.14 mu s, a 5-fold increase with respect to that of the YD-TRC. These results show that YD is a more effective donor in YD-TRC and YD-TRC-AEAQ systems at forming long-lived charge-separated states compared to a previously reported atriphenylamine derivative (MTPA) that generated charge-separated states with a lifetime of 80 ns in MTPA-TRC and 650 ns in MTPA-TRC-AEAQ, The third system was constructed using a metal-free porphyrin derivative (MHTPP) to form a MHTPP-TRC-AEAQ structure, a D-L (linker)-A system with a charge separation lifetime less than 10 ns. Therefore, the D-A(1)-A(2) architecture is the best at generating long-lived charge-separated states and thus is a promising design strategy for organic photovoltaics materials.