Résumé
Photoactive hybrid films based on n type silicon nanowires [SiNWs] dispersed in poly(3-hexylthiophene) [P3HT], a p type conjugated polymer known for its good ordering properties, have a main interest for the production of photovoltaic films at a limited cost. Silicon nanowires synthesized at high yield by the oxide assisted growth technique have been dispersed in tetrahydrofuran: THF, and mixed with a P3HT solution in THF to form a blend of the inorganic-organic components in the appropriate proportions. The blend of SiNWs and P3HT have been deposited by spin coating on PEDOT-PSS/ITO substrates leading to the production of 100 nm thick SiNWs/P3HT thin layers of controlled compositions. The quenching of the P3HT fluorescence has shown the effective dissociation of the photogenerated pairs for an optimum composition of 6 SiNWs vol. % in the blend, which is in accordance with the low percolation threshold expected from the high aspect ratio of the nanowires. Current/voltage experiments under illumination have however led to collected photocurrents remaining limited to some 10 μA/cm2 whereas an interesting open circuit voltage of 0.65 V was obtained. It has been possible from surface potential decay experiments to assign the main limiting process to the low electron transport along nanowires of diameter smaller than 10 nm, whereas easy hole transport in the P3HT thickness was obtained. The high densities of silicon surface states acting as electron traps can simultaneously account for efficient charge pair dissociation and low photocurrents in nanosized structures.