The effect of interfacial diffusion on device performance of polymer solar cells: a quantitative view by active-layer doping

The diffusion of constituent materials at interfaces is one of the key factors for device performance and stability. In this work, the effect of interfacial diffusion of a classic interfacial material PFN on device performance of polymer solar cells was studied quantitatively by doping PFN into active layer based on P3HT:PC61BM blend. The PCEs of devices with 550 ppm PFN decrease to half compared to those of the control devices without PFN, which are mainly attributed to the decrease of short-circuit current (J (sc)) and fill factor (FF). Advanced analyses of equivalent circuit, absorption spectra, and atomic force microscopy indicates that the presence of PFN in the active layer increases the leakage current, decreases the aggregation of P3HT, and reduces the phase separation. This research reveals the physical mechanism of interfacial diffusion in device performance and provides a basis for further improving the performance and stability of PSCs.