Effect of the Energy Level and the Carrier Mobility of the Hole Extraction Layer on the Performance of Planar-mixed Heterojunction Organic Solar Cells

We systematically explored the effect of the electrical property of a homogenously deposited donor layer (H_Donor) on the efficiency of planar-mixed heterojunction organic solar cells. The equivalent circuit model analysis and the dark current characteristics indicate that an increased energy barrier for the electron between the mixed layer and the H_Donor (ΔE_LUMO) decreases the leakage path, thereby resulting in an improved fill factor of the cell. Moreover, the incorporation of H_Donor with high hole mobility (μ_h) to device leads to enhanced charge collecting efficiency and decreased recombination losses. As a result, the device containing H_Donor with high μ_h and ΔE_LUMO showed 28% improvement in power conversion efficiency (5.54%) compared to that of a device with the conventional structure. We believe that this strategy will be a guideline to unlock the full potential of materials in organic solar cells.