New hole transport materials based on polybenzo[1,2-b:4,5-b']dithiophene polymers with different side chains for n-i-p perovskite solar cells

Abstract

A series of new homo- and copolymers P1–P6 with the main chains comprised exclusively of benzo [1,2-b:4,5-b']dithiophene units were synthesized using Stille polycondensation reaction. The optical and electrochemical properties of P1–P6 polymers were studied to estimate the frontier orbitals energies and the Eg values. The obtained data demonstrate the possibility of controlling the electronic properties of polybenzo [1,2-b:4,5-b']dithiophenes by varying only the structure and combinations of solubilizing alkyl side chains. The polymers P1–P6 were evaluated as hole transport materials in n-i-p perovskite solar cells. The highest efficiency of 18.6 % was delivered by the cells with one of the designed polymers with an optimal combination of alternating mono- and dialkylthiophene substituents. The high photovoltaic performance and decent operational stability were achieved using polymer films without any doping, which paves a way to design of inexpensive and scalable dopant-free materials for perovskite solar cells.