Charge Transfer Complexes in Organic−Inorganic Hybrid Blends for Photovoltaic Applications Investigated by Light-Induced Electron Spin Resonance Spectroscopy

So-called charge transfer complexes (CTCs) in plastic solar cell materials have recently become one of the main focuses in research on organic photovoltaics. Because these states influence the relevant parameters of organic solar cells, it is of fundamental interest to understand fully the underlying processes. In the present work, we show that CTC states can be captured by light-induced electron spin resonance (l-ESR) with a much higher sensitivity than is possible with previously applied methods, such as photoinduced absorption spectroscopy. We take advantage of the l-ESR technique to demonstrate the existence of CTC states by their direct excitation with low-energy photons in an organic polymer/fullerene blend and, for the first time, also in hybrid blends of poly(3-hexylthiophene) and CdSe nanoparticles. Moreover, the recombination kinetics is analyzed and discussed.