Asymmetric thieno[2,3-b]thiophene-based electron acceptor featuring a seven fused-ring electron donor unit as core for nonfullerene organic photovoltaics

Abstract

Abstract A n-type organic semiconductor (n-OS) electron acceptor (ITCNTC) based on thieno [2,3-b]thiophene-containing asymmetric seven fused-ring central unit was developed. In comparison with the reported isomer of ITCPTC, ITCNTC exhibits blue-shift absorption spectra and higher LUMO energy level. Organic solar cells (OSCs) based on wide band-gap polymer donor J71 and ITCNTC blends gave power conversion efficiencies (PCEs) of 5.18% without any post-treatment. After thermal annealing (TA), PCE was significantly boosted to 8.52%, with enhanced short circuit current density (JSC) and fill factor (FF). However, the PCE of 8.52% is lower than that of the reported J71:ITCPTC based device (11.63%), which is mainly ascribed to the narrower absorption of ITCNTC and unfavorable morphology. It is noteworthy that the average open circuit voltage (VOC) of the ITCNTC-based device (0.940 V) is 0.06 eV higher than that of the ITCPTC-based device (0.877 V), which is benefitted from the upshifted LUMO energy level of ITCNTC acceptor. These results indicate that the chemical structure of the central fused ring plays a very important role in determining the photovoltaic performance of the n-OS acceptors.