A Furan‐Substituted Polymeric Hole‐Transporting Material for Energy Level Regulation and Less Planarity in Colloidal Quantum Dot Solar Cells

Abstract

For efficient colloidal quantum dot (CQD) solar cells (CQD‐SCs), thiol‐passivated p‐type CQDs are generally used as a hole‐transporting material (HTM); however, there are issues with the control of optoelectrical properties, low thiol passivation rate, and poor morphology with a power conversion efficiency (PCE) of approximately 11%. Although polymeric HTMs have been introduced to address these issues, maximizing efficiency and achieving green‐solvent processability and thermal stability for commercialization is necessary. Here, we synthesize a novel benzodifuran (BDF)‐based HTM (asy‐ranPBTBDF) showing an electron‐deficient state, low steric hindrance, and low planarity compared to those of a typical benzodithiophene (BDT)‐based HTM (asy‐ranPBTBDT). BDF properties lead to deep high occupied molecular orbital (HOMO) levels, close π–π stacking, excellent solubility, and amorphous properties related to efficiency, green‐solvent processability, and thermal stability. With these benefits, the asy‐ranPBTBDF‐based CQD‐SC showed enhanced open‐circuit voltage (VOC) (0.65 V) and PCE (13.29%) compared to those of the asy‐ranPBTBDT‐based device (0.63 V and 12.22%) in toxic processes with chlorobenzene. The asy‐ranPBTBDF‐based CQD‐SC showed a PCE of 12.51% in a green‐solvent process with 2‐methylanisole and improved thermal stability at 80 °C (83.8% retaining after 24 h) owing to less lateral crystallization than the asy‐ranPBTBDT‐based device (60.8% retaining after 24 h).