Donor-Acceptor Type Polymer Bearing Carbazole Side Chain for Efficient Dopant-Free Perovskite Solar Cells

In conventional n-i-p perovskite solar cells (PVSCs), electron donor (D)-acceptor (A) polymers have been found to be potential substitutes for doped spiro-based small molecule hole-transporting materials (HTMs) due to their excellent performance in hole mobility, film formability, and stability. Herein, a benzo[1,2-b:4,5-b ']dithiophene (BDT)-benzodithiophene-4,8-dione (BDD) copolymer PBDB-Cz is developed by employing carbazole as the conjugated side chain of BDT. PBDB-O and PBDB-T with alkoxy and thiophene as the side chain of BDT, respectively, are also synthesized and studied for comparison. The synergistic effect of the carbazole side chain and the BDT-BDD backbone to promote hole transport properties is found in PBDB-Cz. The carbazole side chain enhances both coplanarity and interaction of polymer chains, while simultaneously deepening energy levels and improving the hole mobility of the polymeric HTM. Consequently, PBDB-Cz outperforms two counterparts, exhibiting a promising power conversion efficiency (PCE) of 22.06%. Notably, the PBDB-Cz also improves the device stability, and the devices can retain more than 90% of their initial PCEs after being stored at ambient conditions for 100 days. To the best of the authors' knowledge, this is the first report to incorporate carbazole into D-A polymeric HTM by side chain engineering.