Hybrid Density Functional Study on the Electronic Structures and Properties of P3HT-PbS and P3HT-CdS Hybrid Interface for Photovoltaic Applications

Abstract

The efficiency of charge transport mainly depends on the interfacial energy level alignment between the conjugated polymer and the inorganic substrate. It provides an accurate understanding, predicting as well as controlling the optimal power conversion efficiency of various type of hybrid photovoltaic systems. In this article, we use hybrid functional (HSE06) to study the electronic structures and properties at the interface of poly(3-hexylthiophene)(P3HT)/CdS and P3HT/PbS for solar cell applications. We found that the dangling bonds at the inorganic surface introduce in-gap states and greatly reduce the device performance. We used pseudo-hydrogen atoms as the passivation agent to remove the dangling bonds and eliminate the in-gap states to construct the energy alignment at the hybrid interface. The calculated interfacial density of states reveal a better performance in P3HT/CdS, compared to P3HT/PbS. P3HT/CdS possesses a LUMOP3HT/CBMCdS and HOMOP3HT/VBMCdS energy offset large enough for sufficient exciton separation across the interface and prevents charge recombination. In contrast, the reason for low power conversion efficiency in P3HT/PbS lies on its HOMOP3HT/VBMPbS offset which is too small to break the exciton binding energy for charge separation. Moreover, we reported the dependency of the energy level alignment and open circuit voltage on the interfacial molecular orientations. Our DFT calculation can be used to predict candidate materials for the development of efficiency optoelectronic devices. (C) 2018 Wiley Periodicals, Inc.