  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.

Materials Science;Mesoscale and Nanoscale Physics;Chemical Physics