Thin film solar cells incorporating microcrystalline Si_1–xGe_x as efficient infrared absorber: an application to double junction tandem solar cells

Abstract

We have fabricated efficient ($7-

Fabrication of double- and triple-junction solar cells with hydrogenated amorphous silicon oxide (a-SiOx:H) top cell

“…Therefore, the multi-junction cells can convert photo-generated electron-hole pairs into electricity with reduced thermalization and transmission losses, resulting in higher power conversion efficiency. Various Si-based thin-film double-junction (2J) and triple-junction (3J) solar cells have been proposed: (i) for 2J solar cells: a-Si:H/a-Si:H [1,2], a-Si: H/a-SiGe:H [3,4], and a-Si:H/nc-Si:H [5,6]; and (ii) for 3J solar cells: a-Si:H/a-SiGe:H/a-SiGe:H [7][8][9][10][11], a-Si:H/a-SiGe:H/nc-Si:H [12][13][14][15][16], and a-Si:H/nc-Si:H/nc-Si:H [16][17][18]. The 3J structure a-Si:H/a-SiGe: H/nc-Si:H of Yan et al [19] achieved the world record initial efficiency of 16.3% and the 3J structure a-Si:H/nc-Si:H/nc-Si:H of Kim et al [15] achieved the world record stable efficiency of 13.4% for thin-film silicon solar cells.…”

Effects of process parameters onμc - Si1 − XGeX:H solar cells performance and material properties

“…The crystallinity stays nearly constant in this range, but the germanium content increases. As alloying of μc-Si:H with germanium narrows the band gap and increases the carrier recombination rate it may be responsible for the change in V oc [4].…”

“…Another approach is to increase the absorption coefficient of the absorber material by alloying silicon with germanium. Matsui et al introduced the usage of microcrystalline silicon germanium alloys (μc-SiGe:H) with increased absorption coefficient compared to μc-Si:H [4,5].…”

Geometrical optimization and electrical performance comparison of thin-film tandem structures based on pm-Si:H andμc-Si:H using computer simulation

“…In a conventional tandem device, the two elementary cells are directly stacked by successive layer deposition, which means that they are both optically and electrically coupled [5][6][7]. To provide the current to the load, this structure requires only two contact electrodes connected to the top cell P layer and to the bottom cell N layer.…”

“…In tandem devices, two PIN cells made with materials of different bandgap energies are fabricated in series [5][6][7]. A low bandgap material such as microcrystalline silicon can be used as the bottom cell in conjunction with amorphous silicon (top cell) to extend the spectral range of high collection efficiency [5,8].…”