Charge Photogeneration in Organic Solar Cells

The development of predictive models relating materials' structures to photovoltaic device performance is crucial for the optimization of organic solar cells. Several factors can favor dissociation of interfacial charge-transfer states, including a large overall free energy loss driving charge separation, large domain sizes, and strong macroscopic electric fields. However, in all these cases, modulating these parameters to enhance charge photogeneration may have a negative impact upon other aspects of device performance. Similarly, increasing the domain size to favor CT-state dissociation can reduce the efficiency of exciton diffusion to the interface, while increasing the internal electric field by reducing the photoactive layer thickness would reduce light absorption. Following Onsager theory, charge photogeneration should be favored by reducing the Coulomb binding energy of the CT states. The introduction of insulator layers at the charge separation interface and the use of redox relays both enhance the performance of dye-sensitized solar cells.