Solution-processable porous organic polymer for tailoring the charge transport property of planar perovskite solar cells

Abstract

Herein, a soluble, highly branched, and cross-linked polymer was prepared with alkyl-modified perylene and melamine motifs by adapting the synthetic strategy for porous organic polymers (T-POP). With the expanded surface area of such a polymer relative to the linear one-dimensional conjugated polymers, the intermolecular contact between the optically active units such as perylene motifs in the back bones or branches increased in frequency, resulting in strong π-π stacking, which facilitated the charge charrier transport in planar perovskite solar cells. Additionally, its amorphous nature afforded a smooth surface without severe aggregation, which typically limits the continuous charge carrier pathways. However, the films showed rough surface morphology when the substrates such as indium tin oxide glass with high hydrophilic property were used, while the films showed smooth surfaces when it was deposited on PC70BM, which was one of the device components. Furthermore, by comparing its frontier orbital levels with those of the other components in the devices, it was confirmed that T-POP could be applied as a secondary electron transport layer on the PC70BM layer. As a result, the stability of the perovskite layer increased with a concomitant increase in the hydrophobicity of the top layer with T-POP and the power conversion efficiencies of the functioning devices increased up to 13% with respect to the devices without T-POP enhancing electron transport efficacy.