Hydrogenated microcrystalline silicon germanium: A bottom cell material for amorphous silicon-based tandem solar cells

Abstract

We have developed hydrogenated microcrystalline silicon germanium, which exhibits a red-shifted absorption spectrum relative to hydrogenated microcrystalline silicon, as a candidate material for the bottom cell of amorphous silicon-based tandem solar cells. Optical absorption, x-ray diffraction, and Raman scattering spectra are presented in addition to optoelectronic properties and light-induced changes.

Thin-Film Silicon –Growth Process and Solar Cell Application–

“…38,39) Initially, aSiGe:H was adopted for bottom cell materials; however, this material shows severe photoinduced degradation. 40) Recently, c-Si:H or c-SiGe:H has been proposed as promising candidates for bottom cell materials, [41][42][43] because they do not exhibit photoinduced degradation. In this proposal, a high rate growth of these materials is crucial for low-cost fabrication of tandem solar cells, since c-Si:H as well as c-SiGe:H essentially has an indirect optical-transition nature.…”

“…Several monolayers of amorphous silicon are deposited and these layers are exposed to hydrogen atoms produced in the hydrogen plasma. These procedures are repeated alternately for [40][41][42][43][44][45][46][47][48][49][50] times to obtain the suitable thickness for the evaluation of film structure. The absence of marked reduction of the film thickness during the hydrogen-plasma treatment is difficult to explain by the etching model and hence the chemicalannealing model has been proposed.…”

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

“…When applying our optimized substrates with low reflection and low absorption losses, the even higher J sc up to 25-27 mA/cm 2 can be reached for mc-Si 0 . 9 [12]. The detail of the optimization of single junction devices will be reported elsewhere.…”

“…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].…”

Effect of Ge atoms on crystal structure and optoelectronic properties of hydrogenated Si–Ge films

“…1-7 µc-SiGe:H features a higher absorption coefficient than microcrystalline silicon (µc-Si:H) throughout the solar spectrum, [4][5][6][7][8][9] whereas the optoelectronic quality of the µc-Si 1−x Ge x :H films is usually not satisfactory due to the increased defect density with Ge incorporation. [10][11][12][13] It has been reported that the electronic conductivity in the dark and under illumination depends strongly on the structural composition of µc-Si 1−x Ge x :H films.…”