In-situ investigation of interfacial effects on charge accumulation and extraction in organic solar cells based on transient photocurrent studies

In organic solar cells, the interfacial and bulk photovoltaic processes are typically coupled based on charge transport and accumulation. In this article, we demonstrated that the in situ transient photocurrent measurements can be a powerful approach to separately investigate the interfacial effects on interfacial and bulk photovoltaic process. Based on this method, the effects of interfacial dipoles on charge extraction, accumulation, and recombination are solely studied by comparing Ca and Al devices with standard architecture of ITO/PEDOT/P3HT:PCBM/cathode. We observe that stronger interfacial dipoles can significantly decrease the charge extraction time and consequently increase the charge extraction efficiency. More importantly, stronger interfacial dipoles can also decrease the charge accumulation within the bulk photovoltaic layer. Furthermore, our experimental results indicate that the bulk-accumulated charges can act as recombination centers under device-operating condition, resulting in the recombination loss in photogenerated carriers. Clearly, our studies of transient photocurrents elucidated the charge extraction, accumulation, and recombination in OSCs. (C) 2014 Elsevier B.V. All rights reserved.