Non‐fullerene all small molecule OBHJSCs with profound device characteristics

Abstract

AbstractIn this work, we have reported two donor materials ONAF and SNAF that complement the widely used non‐fullerene acceptor ITIC, with the aim to develop non‐fullerene all small molecule organic bulk heterojunction solar cells (NF‐ASM‐OBHJSCs). Two small molecule donors A‐D‐D'‐D‐A architecture, namely ONAF and SNAF are synthesized and explored their ability to act as donor material along with the ITIC acceptor. Benzodithiophene (BDT) is used as central donor unit (dialkoxy‐BDT for ONAF and Dialkylthiophene‐BDT for SNAF) along with novel naphthodithiophene (NDT) terminal donor to improve light harvesting and charge conducting ability of the donor materials. N‐Butylrhodanine is employed as terminal acceptor to enhance the intramolecular charge transfer (ICT) and to place energy level of the donor materials. Both the small molecule donor materials have good thermal stability, broad and intense absorption displayed in the UV‐vis region with energy levels suitable for ITIC acceptor. NF‐ASM‐OBHJSCs are fabricated by using all small molecules (ONAF & SNAF) as donors and ITIC as acceptor. OBHJSCs based on SNAF displayed superior photovoltaic properties with power conversion efficiency (PCE) as 9.94 % (Jsc = 15.93 mA cm‐2, Voc = 0.96 V and FF = 0.65) compared to ONAF based devices with PCE as 7.48 % (Jsc = 14.93 mA cm‐2, Voc = 0.82 V and FF = 0.61). The substantial high PCE of SANF is attributed to the broad absorption, relatively well‐matched HOMO‐LUMO energy levels between SNAF – ITIC acceptor, better film morphology for efficient charge transport and exciton dissociation at donor/acceptor (D‐A) junction. The observed PCE is one of the best reported for the NDT‐BDT‐based all small molecule non‐fullerene OBHJSCs. Moreover, simplicity in the device fabrication procedures and low energy loss associated are added advantages with the SNAF based devices. We predict that the HOMO‐LUMO levels (CV) of D/A falling in this category, as in Figure S7, with further close energy levels will have implications on the efficiency of OBHJSCs.