A typical bulk heterojunction photovoltaic device contains two materials, a ¿donor¿ material where excitons are produced when light is absorbed and an ¿acceptor¿ material which enables charge separation of the exciton to take place. After excitons are produced in the ¿donor¿ phase, they are converted into closely bound electron¿hole pairs at the donor¿acceptor interface. In an operating solar cell, the bound charge pair states have to dissociate by overcoming the mutual Coulomb attraction between electrons and holes, to form free mobile charges (charge-separated states) that can be extracted as photocurrent. No consensus has yet been reached on how, when and why carriers separate against their mutual Coulomb attraction, to form free independent charges from bound-charge pair states. This proposal seeks to find out of photo-excited musr can measure these charge-transfer processes.