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.

Automated summary

A new copolymer PBDB-Cz with carbazole as the conjugated side chain of BDT has been developed for perovskite solar cells, showing excellent hole transport properties and a promising power conversion efficiency of 22.06%. The incorporation of carbazole improves the coplanarity and interaction of the polymer chains, as well as the hole mobility of the polymeric HTM, leading to enhanced device stability with over 90% of initial PCE retention after 100 days of ambient storage.