Dynamic Coupling between Electrode Interface and Donor/Acceptor Interface via Charge Dissociation in Organic Solar Cells at Device-Operating Condition

Organic solar cells exhibit both electrode/photovoltaic (E/P) interface and donor/acceptor (D/A) interface in controlling the critical photovoltaic processes. Here, on the basis of the efficient PTB7:PC₇₁BM solar cells, our studies on magneto-photocurrent with external bias provide the first evidence that the E/P interface and D/A interface are dynamically coupled at device-operating condition. Specifically, we observe a significant decrease (90%) in the critical bias required to completely dissociate the charge transfer (CT) states at D/A interface by changing the E/P interface with increased interface dipole field from ZnO to the polyelectrolyte (PFN). The experimental results demonstrate that strong dipole field at the E/P interface can effectively decrease the electron–hole binding energy at D/A interface through the enhancement of built-in field applied on CT states. Clearly, our experimental studies provide new insight on the interfacial engineering through addressing the dynamic coupling between E/P interface and D/A interface in organic bulk-heterojunction solar cells toward further improvement on photovoltaic efficiencies.