Hole-transporting interlayers based on pyrazine-containing conjugated polymers for perovskite solar cells

Hybrid organic-inorganic perovskite solar cells (PSCs) have drawn great attention in the past decade due to the rapid growth of their power conversion efficiency (PCE) and the advantage of their low-cost fabrication. The hole-transport materials (HTMs) play a crucial role in achieving high efficiency and operational stability of PSCs. In this work, we report the synthesis of two novel conjugated polymers by coupling of the alkylsilyl-substituted benzo[1,2-b:4,5-b']dithiophene unit with the thiophene-bridged pyrazine block and their investigation as dopant-free HTMs in n-i-p PSCs. The devices with polymer PBPyT-ex (poly[(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo[1,2-b:4,5-b']dithiophene)-alt-5,5'-(2,5-bis(4-(2-ethylhexyl)thiophen-2-yl)pyrazine)]) demonstrate PCEs up to 17.5%, outperforming the 14.9% efficiency of PSCs with PBPyT-in (poly[(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo[1,2-b:4,5-b']dithiophene)-alt-5,5'-(2,5-bis(3-(2-ethylhexyl)thiophen-2-yl)pyrazine)]), which is attributed to the difference in the quality of HTM films. The results obtained feature the combination of pyrazine, thiophene and benzodithiophene units as a successful example of polymeric HTM backbone design for PSCs with encouraging efficiency and high operational stability over 1500 h under continuous illumination.