Electron-Selective Epitaxial/Amorphous Germanium Stack Contact for Organic-Crystalline Silicon Hybrid Solar Cells

Carrier transport properties can be improved through suppressing the charge carrier recombination and decreasing the contact resistance using the proper carrier-selective contact. In this work, an epitaxial/amorphous germanium (epi/a-Ge) stack thin film is introduced into the rear surface of organic–inorganic hybrid (OIH) solar cells as an efficient electron-selective contact. This novel electron-selective stack contact simultaneously contributes low recombinative and resistive losses through a three-material system composed of n-type silicon (n-Si), epitaxial silicon germanium (epi-SiGe), and amorphous germanium (a-Ge), which promotes the tailoring of band structures, the passivation of surface dangle bond defects, and the formation of Ohmic contact. The results show obvious improvement in the open-circuit voltage (Voc) (from 549.5 to 643.0 mV) and fill factor (FF) (from 70.5 to 75.4%), corresponding to the increase in the power conversion efficiency (PCE) of OIH solar cells (from 10.3 to 12.9%). This work indicates novel application of the carrier-selective stack contact to achieve high-performance OIH solar cells with a simple and low-temperature process.