Avadh Baheri Saxena

Photoinduced electron-hole charge separation, intrinsic self-doping and novel device applications of Q1D heterojunction materials: mixed-halide MX solids

Abstract We have extensively studied, both experimentally and theoretically, the following three mixed-halide systems: (i) PtClxBr1−x, (ii) PtClxI1−x and (iii) PtBrxI1−x for a variety of concentrations x. We have obtained direct spectroscopic evidence (vibrational modes) for charge separation from resonance Raman (RR) experiments on doped and photoexcited single crystals of PtClxBr1−x. In particular, electron polarons preferentially locate on the PtBr segment while hole polarons are trapped within the PtCl segments. This polaron charge selectivity, which is potentially very useful for photovoltaic device applications, is demonstrated within theoretical calculations based on a discrete, 3 4 - filled , two-band, tight-binding, extended Peierls-Hubbard model, showing strong hybridization of PtCl and PtBr electronic bands as the driving force for separation. In contrast to PtClxBr1−x, we find that both the PtClxI1−x and the PtBrxI1−x systems exhibit qualitatively different behavior, such as intrinsic ‘self-doping’. In other words, our simulations predict that electronic charge is spontaneously removed from the PtI segment and injected into the PtCl (or PtBR) segment, thus creating hole defects in PtI and electron defects (polarons/bipolarons) in PtCl (or PtBr).