Microcrystalline Silicon-Germanium Alloys for Absorption Layers in Thin Film Solar Cells

Abstract

Thin microcrystalline silicon-germanium films (μ-Sil.xGex:H) prepared by PECVD at 95 MHz have been investigated. The optical absorption of these films increases in the infrared spectral region with increasing germanium content. In addition to the shift of the indirect gap an increase of the absorption coefficient above the band edge is observed. The material shows high crystallinity and exhibits good structural quality similar to pure μ-Si:H films. The films are homogeneous on a macroscopic to a microscopic scale as confirmed by Raman spectroscopy and Electron Microscopy methods. p-i-n solar cells with pc-Sil-xGex:H i-layers have been prepared for the first time. An efficiency of η = 3.1 % under AM1.5 has been obtained for a cell with 150 nm thin i-layer.

Thin film solar cells incorporating microcrystalline Si1–xGex as efficient infrared absorber: an application to double junction tandem solar cells

“…The Ge content in the films was estimated from the peak position of the SiÀSi optical mode (v Si-Si ) in the Raman spectrum according to v Si-Si %520-70x (cm À1 ) [10,13]. In this study, we did not attempt the profiling technique of Ge content during the film deposition, which is known to improve the carrier collection characteristics in hydrogenated amorphous Si 1-x Ge x (a-Si 1-x Ge x :H) solar cells [14].…”

“…Here, we propose an alternative approach, i.e., the absorption enhancement of the bottom cell by alloying with germanium. Hydrogenated microcrystalline Si 1-x Ge x (mc-Si 1-x Ge x :H) alloys have been developed as a narrower variable band gap absorber for multi-junction solar cell application [9][10][11][12]. Recently, we have fabricated p-i-n single junction solar cells incorporating mc-Si 1-enhancement in the infrared response with excellent performance stability under prolonged light soaking [12].…”

Electron spin resonance study of hydrogenated microcrystalline silicon–germanium alloy thin films

“…The lc-Si 1Àx Ge x :H films can be grown at lowtemperature ($200°C) by plasma-enhanced chemical vapor deposition (PECVD), demonstrating the higher absorption coefficients compared to lc-Si:H over the entire solar spectrum [1][2][3][4]. Although this material is advantageous in terms of optical absorption, the photocarrier transport properties of lc-Si 1Àx Ge x :H layers and solar cells degrade severely as the Ge content increases in the film [2][3][4]. Despite the importance of material characterization, the dependence of electronic properties of lc-Si 1Àx Ge x :H upon variation of alloy composition has not been studied in detail.…”

Carrier collection characteristics of microcrystalline silicon–germanium p–i–n junction solar cells

“…However, the achievable efficiency of the a-Si:H/lc-Si:H tandem solar cells is still limited by the lack of infrared response in the lc-Si:H bottom cell owing to its weak infrared absorption. To extend the spectral sensitivities of solar cells into longer infrared wavelengths, we have proposed the application of hydrogenated microcrystalline silicongermanium alloys (lc-Si 1Àx Ge x :H) as a bottom cell material in a triple-junction structure, i.e., a-Si:H/lc-Si:H/lcSi 1Àx Ge x :H. The lc-Si 1Àx Ge x :H films can be grown at low-temperature ($200°C) by plasma-enhanced chemical vapor deposition (PECVD), exhibiting the higher absorption coefficients compared to lc-Si:H over the entire solar spectrum [1][2][3][4]. Although this material is advantageous in terms of optical absorption, the photocarrier collection in lc-Si 1Àx Ge x :H p-i-n solar cells has been shown to degrade severely as the Ge content increases in the i-layer particularly for x > 0.2 [3,4].…”