Air Stable, Efficient Hybrid Photovoltaic Devices Based on Poly(3-hexylthiophene) and Silicon Nanostructures

Efficient, stable hybrid photovoltaic (PV) devices based on poly(3-hexylthiophene) (P3HT) and silicon nanowire arrays (SiNWs) are reported. A two-step, chlorination/methylation procedure is used to convert Si−H bonds into Si−C ones to reduce the velocity of charge recombination at the silicon surface as well as achieve a favorable alignment of band-edge energies. In addition, Pt nanodots (PtNDs) are deposited onto the surface of the SiNWs to further tune the band-edge alignment and passivate nonmethylated silicon sites. Methylated silicon surfaces modified with PtNDs possess a favorable internal electric field in accord with expectations based on the electron affinity (∼3.7 eV) and net positive surface dipole measured on such surfaces by ultraviolet photoemission spectroscopy. This attests to the degree of chemical control that can be exerted over the internal electric field in such systems by surface functionalization. In concert with methyl termination and decoration with PtNDs, hybrid PV devices based on composites of SiNWs and P3HT achieve an external quantum efficiency (EQE) of 76% at 800 nm and a power conversion efficiency (PCE) of 5.9% under simulated air mass 1.5 solar irradiation at 100 mW cm −2 . Moreover, these devices exhibit stable performance for more than 1200 h. In contrast, devices based on composites of hydrogen-terminated planar silicon and P3HT display an EQE of 0.19% at 560 nm and PCE of 0.006%. The ∼800 times enhancement in device performance and improvement in stability are assigned to the facile derivatization of the surface of silicon nanostructures.