Exploration of promising optical and electronic properties of (non-polymer) small donor molecules for organic solar cells

Non-fullerene based organic compounds are considered promising materials for the fabrication of modern photovoltaic materials. Non-fullerene-based organic solar cells comprise of good photochemical and thermal stability along with longer device lifetimes as compared to fullerene-based compounds. Five new non-fullerene donor molecules were designed keeping in view the excellent donor properties of 3-bis(4-(2-ethylhexyl)-thiophen-2-yl)-5,7-bis(2ethylhexyl) benzo[1,2-:4,5-c ']-dithiophene-4,8-dione thiophene-alkoxy benzene-thiophene indenedione (BDD-IN) by end-capped modifications. Photovoltaic and electronic characteristics of studied molecules were determined by employing density functional theory (DFT) and time dependent density functional theory (TD-DFT). Subsequently, obtained results were compared with the reference molecule BDD-IN. The designed molecules presented lower energy difference (Delta Epsilon) in the range of 2.17-2.39 eV in comparison to BDD-IN (= 2.72 eV). Moreover, insight from the frontier molecular orbital (FMO) analysis disclosed that central acceptors are responsible for the charge transformation. The designed molecules were found with higher lambda(max) values and lower transition energies than BDD-IN molecule due to stronger end-capped acceptors. Open circuit voltage (Voc) was observed in the higher range (1.54-1.78 V) in accordance with HOMOdonor-LUMOPC61BM by designed compounds when compared with BDD-IN (1.28 V). Similarly, lower reorganization energy values were exhibited by the designed compounds in the range of lambda(e)(0.00285-0.00370 E-h) and lambda(h)(0.00847-0.00802 E-h) than BDD-IN [lambda(e)(0.00700 E-h) and lambda(h)(0.00889 E-h)]. These measurements show that the designed compounds are promising candidates for incorporation into solar cell devices, which would benefit from better hole and electron mobility.

Automated summary

Five new non-fullerene donor molecules were designed through end-capped modifications, showing better photovoltaic and electronic characteristics compared to traditional fullerene-based donors. These designed molecules have lower energy differences, higher λ(max) values, and improved open circuit voltages (Voc), making them promising candidates for incorporation into solar cell devices with enhanced hole and electron mobility.