Investigation of light induced charge carrier generation in polymer/nanoparticle blends

Organic photovoltaics are a promising approach for a cheap and easy-to-produce alternative for inorganic semiconductor solar cells. In such cells the photoactive layer consists of a polymer donor and a fullerene acceptor. Their disadvantage lies in a low power conversion efficiency which has to increase significantly for industrial purposes. For such a performance improvement, new approaches were suggested, e.g. the exchange of the acceptor material with semiconducting inorganic nanoparticles (NP). A detailed knowledge of the internal electronical processes like exciton separation and charge carrier transport in such hybrid systems is needed to find ways for further cell optimization. An important technique to investigate the charge separation process between the acceptor and donor materials is Light induced Electron Spin Resonance (LESR). Photoinduced excitons are separated at the interface of NP and polymer. These free polarons have a net spin which can be detected by ESR. We present LESR measurements on polymer:CdSe and polymer:CdTe blends. Time resolved experiments show an increased amount of trap states in comparison to polymer:PCBM blends.