Design Simulation and Optimization of Germanium-Based Solar Cells with Micro-Nano Cross-Cone Absorption Structure

In this paper, germanium-based solar cells were designed based on germanium (Ge) materials, and the cross-cone (CC) nanostructures were used as the absorber layer of the solar cells. The optical path inside the absorber layer was increased by microstructure reflection, thereby increasing the absorption efficiency of the germanium-based solar cell. The reflectivity, transmittance, electric field and magnetic field of the corresponding position of the device were simulated and calculated by the finite difference time domain (FDTD) method. By simulating doping and simulating the external potential difference, the short-circuit current density (JSC), open-circuit voltage (VOC), output power and photoelectric conversion efficiency (η) of the device were calculated. The study found that for the entire study wavelength range (300–1600 nm), the transmittance of the device was close to none, and the average light absorption rate under air mass 1.5 global (AM1.5G) was 94.6%. In the light wavelength range from 310 nm to 1512 nm with a width of 1201 nm, the absorption rate was greater than 90%, which is in line with the high absorption of the broadband. Among them, the absorption rate at 886 nm reached 99.84%, the absorption rate at 1016 nm reached 99.89%, and the absorption rate at 1108 nm reached 99.997%, which is close to full absorption. By exploring the electrical performance of the device under different Ge nanostructure parameters, a germanium-based solar cell device under the nanocross-cone absorption structure array with both high-efficiency light absorption and excellent electrical performance was finally obtained. The study shows that the VOC of its single-junction cell was 0.31 V, JSC reached 45.5 mA/cm2, and it had a fill factor (FF) of 72.7% and can achieve a photoelectric conversion efficiency of 10.3%, surpassing the performance of most Ge solar cells today.