# Modeling spontaneous charge transfer at metal/organic hybrid heterostructures

## TL;DR

This study investigates how the conformational regularity of P3HT affects charge transfer at metal/organic interfaces, using DFT calculations and vibrational spectroscopy to link interfacial electronic states with polymer structure.

## Contribution

It demonstrates that regio-randomness in P3HT modifies interfacial charge transfer and electronic coupling, providing a spectroscopic method to assess charge transfer levels.

## Key findings

- Regio-randomness reduces interfacial electronic state intensity.
- Non-resonant HD-VSFG signal correlates with charge transfer level.
- Charge transfer can be quantified via non-resonant response measurement.

## Abstract

Hybrid materials are crucial in photovoltaics where the overall efficiency of the heterostructure is closely related to the level of charge transfer at the interface. Here, using various metal / poly(3-hexylthiophene)(P3HT) heterostructure models, we reveal that the level of spontaneous charge transfer and electronic coupling at these interfaces depend on the conformational regularity of the organic polymer deposited on the metal substrate. Using ab-initio quantum chemical calculations based on density functional theory (DFT) and heterodyne vibrational sum frequency generation (HD-VSFG) measurements, we show that inducing regio-randomness into the organic polymer modifies the intensity of interfacial electronic states, level of hybridization, density of interfacial charge transfer and the electronic wave function of the material. We present the HD-VSFG responses of the metal/P3HT heterojunctions containing both regio-regular and regio-random P3HT structures and show that the amount of non-resonant signal is closely related to the level of the spontaneous charge transfer at the interface. Thus, by measuring the non-resonant response of the metal/P3HT heterojunctions, the level of spontaneous charge transfer at the interface can be determined.