Tandem Junction Thin Film Solar Cells with Hydrogenated Microcrystalline Silicon Germanium as Bottom Cell Absorber Layer by RF PECVD

Hydrogenated microcrystalline silicon germanium (μc-SiGe:H) alloy can absorb long-wavelength solar spectrum with lower optical bandgap and higher absorption coefficient in full wavelength range and has been explored with many techniques both in industry and in academia. In this paper, the process of intrinsic μc-SiGe:H is developed with Applied Materials’ AKT 4300 radio-frequency (13.56MHz) PECVD system to replace the commonly used hydrogenated microcrystalline silicon (μc-Si:H) as the bottom cell absorber layer. 11.72mA/cm2 short circuit current density (Jsc) is measured with 1.2μm thick μc-SiGe:H layer without doing any optimization at the device level. It provides 4.4% higher current compared to its silicon counterpart with 1.95μm thickness. The quantum efficiency measurement shows gain in the wavelength range from 600nm to 1100nm. Thickness variation over the 30cmx30cm module area is controlled small than 3.1%. The uniformity is also confirmed with the segment measurement at different locations of the module.