Effect of Triplet State on the Lifetime of Charge Separation in Ambipolar D‑A₁‑A₂ Organic Semiconductors

An ambipolar organic semiconductor with styrene based triphenylamine derivative (MTPA) as an electron donor (D), triazine group (TRC) as an electron acceptor (A₁), and 9,10-anthraquinone (AEAQ) as a second electron acceptor (A₂) has shown an 8-fold increase in the lifetime of charge separation with a high performance as solar cell materials with respect to the D-A₁ architecture and demonstrated a general D-A₁-A₂ architecture as a promising materials design strategy for photovoltaics. Here we synthesized and characterized two new D-A₁-A₂ compounds with perylene bisimide derivatives (PDI and PBI) as A₂ using an integrated experimental and computational method to study and compare the kinetics of three MTPA-TRC-A₂ systems. A two-step sequential decay pathway was observed in both MTPA-TRC-PDI and MTPA-TRC-PBI but a direct decay pathway in MTPA-TRC-AEAQ. The charge separated state with a lifetime of 22 ns in the PDI system and 75 ns in the PBI system relaxes to the corresponding triplet state followed by the decay to ground state in 827 ns and 29.2 μs, respectively. Thus, a triplet state with a lower energy than the charge separated state shortens the lifetime of the charge separated state but increases the overall lifetime of excited states

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 (A₁), and 9,10-anthraquinone (AEAQ) as a second acceptor (A₂) in constructing two systems, YD-TRC and YD-TRC-AEAQ. The lifetime of the photoinduced charge-separated states in YD-TRC, a D–A₁ system, was found to be 215 ns and that in YD-TRC-AEAQ, a D–A₁–A₂ system, to be 1.14 μs, 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–A₁–A₂ architecture is the best at generating long-lived charge-separated states and thus is a promising design strategy for organic photovoltaics materials

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 (A₁), and 9,10-anthraquinone (AEAQ) as a second acceptor (A₂) in constructing two systems, YD-TRC and YD-TRC-AEAQ. The lifetime of the photoinduced charge-separated states in YD-TRC, a D–A₁ system, was found to be 215 ns and that in YD-TRC-AEAQ, a D–A₁–A₂ system, to be 1.14 μs, 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–A₁–A₂ architecture is the best at generating long-lived charge-separated states and thus is a promising design strategy for organic photovoltaics materials