Backbone Randomization in Conjugated Polymer-Based Hole-Transport Materials to Enhance the Efficiencies of Perovskite Solar Cells

The power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) using conjugated polymers (CPs) as hole-transport materials (HTMs) have been drastically enhanced. This is mainly attributed to the development of CPs with high charge mobilities. In PSCs, HTMs play important roles in extracting and transporting photo-generated holes from the perovskite layer. Thus, enhancing both charge transport in the HTM and charge transfer at the HTM/perovskite interface would be more beneficial than improving the charge transport only to enhance the PCEs of PSCs. In this study, we report two different CPs (RP33 and RP-OR) with random configurations synthesized by introduction of new units in a random manner and rearrangement of the backbone units, respectively. Both CPs exhibited better vertical charge transport and charge transfer at the interface with the perovskite layer than do their regular counterparts (P3HT and P-OR). As a result, the PCEs of the dopant-free PSCs with RP33 (16.44%) or RP-OR (19.06%) increased compared to those of the PSCs based on P3HT (15.36%) or P-OR (16.49%), respectively. Furthermore, the FAPbI3-based device with the dopant-free RP33 yielded a PCE of over 20%. These key findings, together with systematic investigations on the morphologies and electrical properties of the two pairs of CPs (P3HT vs RP33 and P-OR vs RP-OR), provide valuable insights into the impact of polymer configuration and present design rationales to achieve CPs as HTMs for efficient PSCs.