Efficiency improvement of organic solar cells by tuning hole transport layer with germanium oxide

Improving optical property is critical for optimizing the power conversion efficiency of organic solar cells. In the present research, we show that modification of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layer with GeO ₂ leads to 15% improvement of power conversion efficiency in a polymer solar cells through enhancement of short circuit currents. Modified PEDOT:PSS layer with optimized concentration of GeO ₂ assists active layer absorbing much light by playing a role of optical spacer. Using AFM and grazing incidence X-ray diffraction (GIXD) data, we also present the evidence that an addition of GeO ₂ does not affect crystallinity of active layer.