Small-Size Effects on Electron Transfer in P3HT/InP Quantum Dots

Abstract

The charge carrier photogeneration yield in hybrid polymer/nanocrystal solar cells strongly depends on the interplay between charge transfer across quantum dot (QD) organic capping layers and quantum confinement effects related to the QD size. Here we combine femtosecond transient spectroscopy and density functional theory (DFT) calculations to improve the understanding of charge transfer dynamics at P3HT/InP QD heterointerfaces as a function of core size (2.5 vs 4.5 nm) and length of the surface ligands (oleylamine vs pyridine). We find that, for large core QDs, the polaron generation yield in P3HT is enhanced by efficient exciton dissociation and charge transfer, and is limited by the length of the ligands. Conversely, for smaller size QDs, electron injection from P3HT to InP cores becomes inefficient due to the unfavorable interfacial energetics, even with short pyridine ligands. Thus, we suggest that both QD surface ligand functionalization and core size should be optimized simultaneously for the design of high-performance hybrid nanocrystal/polymer solar cells.