Composites of conjugated polymers and inorganic nanostructures have attracted wide interest because they can combine the desirable properties of both materials to produce efficient hybrid photovoltaic (PV) devices. 1À4 Conjugated polymers are readily processed to form films of large area, and their absorption coefficients are large so that only thin films are required for light harvesting in PV devices. The electronic and optical properties of inorganic nanostructures can be tuned simply by changing their dimensional shape and size, leading to efficient light harvesting and charge transport. The bandgap and offset of conjugated polymers and inorganic nanostructures are such that charges are separated across the organic/ inorganic interface. The effects of the shape of the inorganic semiconductor nanocrystals, choice of conjugated polymer, and fabrication process on device performance have been investigated in detail, leading to a current state-of-the-art power conversion efficiency (PCE) of 3.1%. 5 A multitude of PV structures have been developed by combining conjugated polymers with various inorganic nanostructures such as CdSe, 5,6 TiO 2 , 7,8 ZnO, 9 PbS, 10 PbSe, 11 Ge 12 and Si 13À17 to achieve highly efficient charge separation/transport.

Photoelectrochemical (PEC) cells based on silicon nanowire arrays (SiNWs) have, to date, exhibited modest power conversion efficiency (PCE) and suffered serious degradation, though they exhibit advantageous properties of charge-transfer/transport properties at the radial-junction and strong light-trap capabilities. The main challenge for this low-cost PEC cell is the surface photooxidation and photocorrosion of the silicon surface when contacting with the electrolyte. In this report, SiNWs derivatized with covalently attached methyl groups, prepared via a two-step chlorination/methylation procedure, demonstrate excellent stability even in the presence of water. Furthermore, SiNWs PEC cells utilizing a room temperature ion liquid (IL) acting as an electrolyte solvent display neglectable surface oxidation. A PEC cell based on a platinum (Pt) nanodots decorated and methylated (-CH(3)) SiNWs electrode in combination with an IL electrolyte yields a PCE of 6.0% and shows excellent stability under simulated air mass (AM) 1.5 solar spectrum irradiation, while the PCE of a PEC cell based on planar silicon only exhibits 0.003%. The inherent performance of these structures indicates that a -CH(3) (Pt) SiNWs electrode in combination with an IL is a new approach to develop a high-performance and low-cost solar cell.

We demonstrate a hybrid Schottky junction solar cell based on methyl/allyl groups terminated silicon nanowire arrays (SiNWs) and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) with a power conversion efficiency (PCE) of 10.2%. The methyl/allyl organic monolayer on silicon can act as an excellent passivation layer for suppressing surface charge recombination, which is characterized by grazing angle attenuated total reflectance Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements. The transient and steady electric output characteristics measurements indicate that the density of trap states of SiNWs are dramatically suppressed by methyl/allyl surface modification. In addition, the device based on methyl/allyl passivated SiNWs exhibits improved stable electrical output over those based on either methyl or allyl passivated ones. The improved PCE and good stability of the device are ascribed to efficient functionalization of the SiNW surface.

Hybrid solar cells based on composites of silicon nanopillar arrays (SiNPs) on silicon substrates and conjugated polymer were investigated in this study. SiNPs with three dimensional (3D) geometry could orthogonalize the directions of light absorption and charge transfer while allowing for enhanced light scattering and trapping. In addition, SiNPs were fabricated by a simple process at low temperature and displayed strong light trapping capability over a wide range of incidence angles as well as near infrared light absorption. Furthermore, a method to control the density of SiNPs had been developed to obtain pillar arrays with controllable distance, which allowed conjugated polymer to reach the bottom part of SiNPs. The thickness of organic layer played a critical role on the short-circuit current, open-circuit voltage and fill factor, and optimum thickness was indispensable to achieve the superior performance. A power conversion efficiency of 9.2% was achieved based on the heterojunction with organic thin layer under AM 1.5G illumination at 100 mW cm À2 . We believe that this model is appropriate for the fabrication of heterojunction hybrid devices based on alternative organic semiconductors or even inorganic semiconducting nanocrystals.

Hybrid organic-inorganic photovoltaic devices based on nanostructured silicon and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid devices present excellent light harvesting capabilities as well as a simple fabrication process. Unlike the metal/Si junction, PEDOT:PSS solution can be solution-casted onto the silicon surface structure to build up hybrid photovoltaic devices without using vacuum deposition techniques. Detailed electronic characterization at PEDOT:PSS/Si heterojunctions is indispensable for achieving a high-performance device. In this paper, the electronic properties of current-voltage, capacitance-voltage, and internal quantum efficiency are characterized in order to explore the organic-inorganic heterojunctions properties. The interfacial defect state density (Dit) of hybrid organic-inorganic photovoltaic devices as well as majority carrier charge transfer velocity (vn) has been extracted from the electrical measurement results. It has been found that less Dit and lower vn can lead to improved electric output characteristics of the organic-inorganic heterojunctions photovoltaic devices, which is ascribed to suppressed charge recombination at the organic-inorganic interface.