Very-high-efficiency double-heterostructure copper phthalocyanine/$C60$ photovoltaic cells

We demonstrate an external power conversion efficiency of $(3.6±0.2)%$ under AM1.5 spectral illumination of 150 mW/cm² (1.5 suns) with vacuum-deposited copper phthalocyanine/$C60$ thin-film double-heterostructure photovoltaic cells incorporating an exciton-blocking layer (EBL). We show that the anode work function influences the photocarrier collection characteristics through the built-in electric field. The cell parameters are less sensitive to the cathode work function, which is attributed to cathode-induced defect states in the EBL energy gap. The presence of these defect states also explains the surprisingly low resistance of the EBL to electron transport. We anticipate significant further improvements in power conversion efficiency by employing optimal structures in light-trapping geometries.