Formation of porous silicon for large-area silicon solar cells: A new method

Luminescent porous silicon (PS) was prepared for the first time using a spr aying set-up, which can diffuse in a homogeneous manner HF solutions, on te xtured or untextured (1 0 0) oriented monocrystalline silicon substrate. Th is new method allows us to apply PS onto the front-side surface of silicon solar cells, by supplying very fine HF drops. The front side of N+/P monocr ystalline silicon solar cells may be treated for long periods without alter ing the front grid metallic contact. The monocrystalline silicon solar cell s (N+/P, 78.5 cm(2)) which has undergone the HF-spraying were made with a v ery simple and low-cost method, allowing front-side Al contamination. A poo r but expected 7.5% conversion efficiency was obtained under AM1 illuminati on. It was shown that under optimised HF concentration, HF-spraying time an d flow HF-spraying rate, Al contamination favours the formation of a thin a nd homogeneous hydrogen-rich PS layer. It was found that under optimised HF -spraying conditions, the hydrogen-rich PS layer decreases the surface refl ectivity up to 3% (i.e., increase light absorption), improves the short cir cuit current (I-SC), and the fill factor (FF) (i.e., decreases the series r esistance), allowing to reach a 12.5% conversion efficiency. The dramatic i mprovement of the latter is discussed throughout the influence of HF concen tration and spraying time on the I-V characteristics and on solar cells par ameters. Despite the fact that the thin surfae PS layer acts as a good anti -reflection coating (ARC), it improves the spectral response of the cells, especially in the blue-side of the solar spectrum, where absorption becomes greater, owing to surface band gap widening and conversion of a part of UV and blue light into longer wavelengths (that are more suitable for convers ion in a Si cell) throughout quantum confinement into the PS layer. (C) 199 9 Elsevier Science B.V. All rights reserved.