Conjugated Polyelectrolyte Combined with Ionic Liquid as the Hole Transport Layer for Efficient Inverted Perovskite Solar Cells

Conjugated polyelectrolytes (CPEs) are promising hole transport materials for perovskite solar cells, whereas their severe intermolecular aggregation significantly affects the device performance. Here, long-chain alkyl imidazolium ionic liquid (IL) of 1-dodecyl-3-methylimidazolium bromide ([C 12 mim]Br) and conjugated polyelectrolytes of potassium poly[3-(4-carboxylatebutyl)thiophene (P3CT-K) are combined with different mass ratios. The UV–vis spectra and dynamic light scattering studies indicate that the aggregation behavior of P3CT-K is suppressed by IL, thus obtaining a smoother hole transport layer for the latter device fabrication, which efficiently improves the film quality of perovskite absorber and enhances the hole transport at the interface. As a consequence, the inverted PSCs based on P3CT-K/IL film as the HTL show considerable improvement in power conversion efficiency (PCE), from 16.21% to 18.81%, compared with pristine P3CT-K based device. These findings indicate that IL can effectively inhibit the aggregation of CPEs, providing a new pathway to further improve the performance of PSCs based on CPEs interlayer.