Efficient quantum theory for studying cold charge-transfer state dissociations in donor-acceptor heterojunction organic solar cells

In donor-acceptor (D-A) heterojunction organic solar cells, hot and cold charge transfer (CT) states are formed at the interface as the precursor for subsequent charge separations. Hot CT states dissociate easily because they are loosely bound, while for cold CT states, the origin of their high-efficiency charge separations still remains heavily debated. Here, we propose a simple but effective methodology that can be used to simulate the cold CT dissociation process and, thereby, the multiple factors which may essentially affect the charge separation efficiency and can be conveniently investigated. The energy barriers on the path from cold CT to the separated charges are analyzed by calculating the adiabatic potential energy surfaces of the lowest-energy excitonic state. The calculation results indicate that the D-A molecular coupling strength and coupling area, D-A energetic offset, charge carrier delocalizations, interfacial Coulomb screening strength, and interfacial disorders can essentially affect the charge separation efficiency of a cold CT state.