Rational design of two-dimensional PDI-based small molecular acceptor from extended indacenodithiazole core for organic solar cells

A pair of linear two-dimensional conjugated non-fullerene acceptors, named as TVIDTPDI and TVIDTzPDI, which have the same perylene diimide end-capping groups, but different in two-dimensional conjugated central core (the dithienyl vinylene-fused indacenodithiophene or dithienyl vinylene-fused indacenodithiazole), were successfully synthesized and evaluated as acceptor materials in organic solar cells (OSCs). Such core units in these small acceptors play a decisive role in the formation of the nanoscale separation of the blend films, which were systematically investigated through absorption spectra, electrochemical properties, density functional theory calculations, AFM images, and charge mobility measurement by space-charge-limited current SCLC method. By incorporation of the dithienyl vinylene-fused indacenodithiazole-based core, TVIDTzPDI showed better planarity in the core unit with a dihedral 45.4° and 49.6° angle of between central core and the PDI. Moreover, the TVIDTzPDI blend with PTB7-Th displays higher and more balanced mobilities (μ_h = 4.56 × 10⁻⁴ and μ_e = 6.12 × 10⁻⁴ cm² V⁻¹ s⁻¹) in comparison with those of TVIDTPDI blend with PTB7-Th. Therefore, the TVIDTzPDI/PTB7-Th based OSCs showed a higher PCE of 2.09% than that of the TVIDTPDI/PTB7-Th devices (1.50%). The purpose of this study is to provide a facile strategy to design PDI-based two-dimensional conjugated small molecular acceptors and understand the impact of installing the two dimensional core and more electron-deficient thiazole unit in such small molecular acceptors.