Keywords: 
• 氢化微晶硅锗 /
• 近红外响应 /
• 硅基薄膜太阳电池 /
• 等离子体增强化学气相沉积

Abstract: Hydrogenated microcrystalline silicon germanium (μc-Si1?xGex:H) thin films have been developed as alternative bottom sub-cell absorbers for multi-junction thin film silicon solar cells due to their narrower band-gaps and higher absorption coefficients than conventional hydrogenated microcrystalline silicon (μc-Si:H) thin films. However, since the structure complexity was increased a lot by Ge incorporation, the influences of μc-Si1?xGex:H film properties on Ge composition have not been understood yet. In this work, μc-Si1?xGex:H thin films with various Ge content and similar crystalline volume fraction are fabricated by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD). The evolutions of μc-Si1?xGex:H material properties by Ge incorporation are characterized by X-ray fluorescence spectrometry, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, absorption coefficient spectrum, and conductivity measurement. The results show that the properties of μc-Si1?xGex:H thin films are strongly determined by Ge content. With the increase of Ge content, the absorption coefficient, (111) grain size, microstructure factor, and dark conductivity of μc-Si1?xGex:H thin films increase, while the H content, (220) grain size, and photosensitivity of μc-Si1?xGex:H thin film decrease. Then, μc-Si1?xGex:H is used as the intrinsic layer in the single junction solar cells. The performances of μc-Si1?xGex:H solar cells with different Ge content and two types of transparent conductive oxide (SnO2 and ZnO) substrates are systematically studied. The results indicate that although μc-Si1?xGex:H thin films become more defective and less compact with Ge incorporation, μc-Si1?xGex:H solar cells exhibit a significant improvement in near-infrared response, especially under the circumstances of thin cell thickness and inefficient light trapping structure. Meanwhile, by using ZnO substrates, initial efficiencies of 7.15%(Jsc=22.6 mA/cm2, Voc=0.494 V, FF=64.0%) and 7.01%(Jsc=23.3 mA/cm2, Voc=0.482 V, FF=62.4%) are achieved by μc-Si0.9Ge0.1:H solar cell and μc-Si0.73Ge0.27:H solar cell, respectively. Furthermore, the μc-Si0.73Ge0.27:H solar cell is used as the bottom sub-cell of the double-junction solar cell, and a Jsc.bottom of 12.30 mA/cm2 can be obtained with the bottom sub-cell thickness as thin as 800 nm, which is even higher than that of μc-Si:H bottom sub-cell with 1700 nm thickness. Finally, an initial efficiency of 10.28%is achieved in an a-Si:H/μc-Si0.73Ge0.27:H double junction cell structure. It is demonstrated that by using the μc-Si1?xGex:H solar cell as the bottom sub-cell in multi-junction thin film silicon solar cells, a higher tandem cell performance can be achieved with a thin thickness, which has a great potential for cost-effective photovoltaics.