NOVEL LIGHT-TRAPPING SCHEMES INVOLVING PLANAR JUNCTIONS AND DIFFUSE REAR REFLECTORS FOR THIN-FILM SILICON-BASED SOLAR-CELLS

Optical optimization of planar junction amorphous and microcrystalline silicon-based thin-film solar cells offers improved conversion effici ency. Planar junction solar cells with diffuse and selective angle rea r reflectors were examined in detail. The refractive index of the diff user material needs to be as close to that of silicon as possible. Ins ulating diffuse rear reflectors must be used in conjunction with condu ctive rear-window layers of the appropriate band gap, conductivity and refractive index. The refractive index of the rear window layer shoul d be at least as large as that of the diffuser material. Rear windows comprised of ZnS, CdS and ZnSe (as well as other II-VI semiconductors and semiconductor alloys) used with a TiO2 diffuse reflector could inc rease the current of optically thin silicon solar cells beyond that po ssible using rough TCO/glass substrates. Selective angle reflectors mu st also be comprised of either the solar cell semiconductor itself (no t possible in many cases) or comprised of a material having properties similar to those of the conducting rear windows used with the diffuse reflectors.