Benzodithiophene-thienopyrroledione-thienothiophene-based random copolymeric hole transporting material for perovskite solar cell

Hole transport materials (HTMs) with different hole extraction abilities play an important role in dictating the efficiency of the perovskite solar cells (PSCs). Besides, employing a donor acceptor (D-A) random copolymer HTM to bring out deeper HOMO energy level is highly beneficial to the hole extraction and durability of PSCs. In this context, a highly soluble D-A based random copolymeric benzodithiophene-thienopyrroledione-thienothiophene derivatives (RCP-BTT) HTM has been derived from the backbone structure of Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7). The synthesized dopant-free RCP-BTT HTM shows a deeper HOMO energy level (-5.28 eV) due to its high compatibility than PTB7 level (-5.15 eV) based on perovskite energy level. Gradient band alignment of RCP-BTT has provided efficient hole extraction in the PSCs made of Cs-containing triple cation perovskite as absorber resulting in the efficient photovoltaic performance of RCP-BTT. The RCP-BTT with dopant shows significantly increased V-oc (1.09 V) with respect to that of parent PTB7 (V-oc of 1.06 V), resulting in an enhanced efficiency of 14.57% than that of PTB7 (12.02%). On the whole, the improvement in photovoltaic performance of PSC based on the polymeric RCP-BTT HTM is attributable to its deeper HOMO energy level and exceptional hole extraction ability.