Effects of cathode modification using spin-coated lithium acetate on the performances of polymer bulk-heterojunction solar cells

In this report, we show that the performances of polymer bulk-heterojunction solar cells were improved by inserting thin films of lithium acetate layers between the active layer and the cathode using a spin-coating process. Comparing with the device without the cathode modification, significant enhancements of Voc (open circuit voltage) from 0.42 V to 0.55 V and device efficiency from 1.4% to 4.1% were achieved. X-ray and ultraviolet photoelectron spectroscopic studies indicate that both the improved damage tolerance of the active layer under the thermally evaporated metal and an n-type doping at the metal/organic interface play the crucial roles in the enhanced performances.