Silicon–organic pigment material hybrids for photovoltaic application

Hybrid materials of silicon and organic dyes have been investigated for possible application as photovoltaic material in thin film solar cells. High conversion efficiency is expected from the combination of the advantages of organic dyes for light absorption and those of silicon for charge carrier separation and transport. Low temperature remote hot wire chemical vapor deposition (HWCVD) was developed for microcrystalline silicon (μc-Si) deposition using SiH4/H2 mixtures. As model dyes zinc phthalocyanines have been evaporated from Knudsen type sources. Layers of dye on μc-Si and μc-Si on dye films, and composites of simultaneously and sequentially deposited Si and dye have been prepared and characterized. Raman, absorption, and photoemission spectroscopy prove the stability of the organic molecules against the rough HWCVD-Si process. Transient microwave conductivity (TRMC) indicates good electronic quality of the μc-Si matrix. Energy transfer from dye to Si is indicated indirectly by luminescence and directly by photoconductivity measurements. FxZnPc pigments with x=0,4,8,16 have been synthesized, purified and adsorbed onto H-terminated Si(1 1 1) for electronic state line up determination by photoelectron spectroscopy. For x=4 and 8 the dye frontier orbitals line up symmetrically versus the Si energy gap offering similar energetic driving forces for electron and hole injection, which is considered optimum for bulk sensitization and indicates a direction to improve the optoelectronic coupling of the organic dyes to silicon.