Organic–inorganic hybrid solar cells were expected to adopt the advantages of both organic and inorganic materials. Due to several crucial problems, the power conversion efficiency of most hybrid solar cells was lower than 1%. Recent work reported the highest power conversion efficiency of a hybrid solar cell as 11.3%, which increased the research interest into organic–inorganic hybrid solar cells. This article focuses on the progress in state-of-the-art research on organic–inorganic hybrid solar cells and the associated key issues, including the energy band alignment of the organic and inorganic components, interface control of the heterojunction, and the use of ordered nanostructures were discussed. The challenges and prospects for organic–inorganic hybrid solar cells in the near future are discussed.

Recent progress in organic–inorganic hybrid solar cells

Dynamic shadowing growth is a simple and powerful nanofabrication technique that combines oblique angle deposition with substrate manipulation in a thin film deposition system, which mainly utilizes self-shadowing effect to form well-aligned nanorod arrays. Many unique nanostructures have been fabricated or designed by properly programming the substrate motions, deposition sources, deposition rates, and shadowing effects in multi-step shadowing growth processes. The formed nanostructures have found many promising applications such as chemical and biological sensors, energy storages, nanomotors, etc., due to their unique characteristics of well-controlled morphologies, structures, and compositions. This review is focused on the design and fabrication of both compositionally and morphologically complex nanostructure arrays by multilayer and co-deposition shadowing growth techniques, and the emphasis will be put on the design and fabrication of multi-component nanostructures with different morphologies.

Advanced multi-component nanostructures designed by dynamic shadowing growth

Integration of silicon nanowires in solar cell structure for efficiency enhancement: A review

Hybrid solar cells with an energy conversion efficiency of 1.04% were fabricated by spin-coating poly(3-hexylthiophene) (P3HT) polymer onto vertically aligned n-type GaAs nanowire arrays synthesized by molecular beam epitaxy. Experimental parameters such as the P3HT solvent mixing ratio of chlorobenzene to dichlorobenzene and nanowire surface etching were studied with a view to improving the energy conversion efficiency.

https://iopscience.iop.org/article/10.1088/0957-4484/20/46/465205/pdf

A GaAs nanowire/P3HT hybrid photovoltaic device.

In this study, we show that the correct determination of surface morphology using scanning force microscopy (SFM) imaging and power spectral density (PSD) analysis of the surface roughness is an extremely demanding task that is easily affected by experimental parameters such as scan speed and feedback parameters. We present examples were the measured topography data is significantly influenced by the feedback response of the SFM system and the PSD curves calculated from this experimental data do not correspond to that of the true topography. Instead, either features are "lost" due to low pass filtering or features are "created" due to oscillation of the feedback loop. In order to overcome these serious problems we show that the interaction signal (error signal) can be used not only to quantitatively control but also to significantly improve the quality of the topography raw data used for the PSD analysis. In particular, the calibrated error signal image can be used in combination with the topography image in order to obtain a correct representation of surface morphology ("true" topographic image). From this "true" topographic image a faithful determination of the PSD of surface morphology is possible. The corresponding PSD curve is not affected by the fine-tuning of feedback parameters, and allows for much faster image acquisition speeds without loss of information in the PSD curve.

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Nanoscale measurement of the power spectral density of surface roughness: how to solve a difficult experimental challenge

A radial p-n junction solar cell based on vertically free-standing silicon nanowire (SiNW) array is realized using a novel low-temperature and shallow phosphorus doping technique. The SiNW arrays with excellent light trapping property were fabricated by metal-assisted chemical etching technique. The shallow phosphorus doping process was carried out in a hot wire chemical vapor disposition chamber with a low substrate temperature of 250°C and H2-diluted PH3 as the doping gas. Auger electron spectroscopy and Hall effect measurements prove the formation of a shallow p-n junction with P atom surface concentration of above 1020 cm−3 and a junction depth of less than 10 nm. A short circuit current density of 37.13 mA/cm2 is achieved for the radial p-n junction SiNW solar cell, which is enhanced by 7.75% compared with the axial p-n junction SiNW solar cell. The quantum efficiency spectra show that radial transport based on the shallow phosphorus doping of SiNW array improves the carrier collection property and then enhances the blue wavelength region response. The novel shallow doping technique provides great potential in the fabrication of high-efficiency SiNW solar cells.

/pdf/realization-of-radial-p-n-junction-silicon-nanowire-solar-4k0dw86h10.pdf

Realization of radial p-n junction silicon nanowire solar cell based on low-temperature and shallow phosphorus doping.

The hydrogenated amorphous silicon thin films with heavily Ti doping were deposited by combination of hot-wire chemical vapor deposition and magnetron sputtering. The sheet resistance for as-deposited heavily Ti-doped amorphous silicon thin films exhibits typical semiconductor features. However, the electrical properties of crystallized Ti-doped silicon thin film by pulse laser melting shows the metal-like behavior, which indicates the happening of an insulator-to-metal transition with the crystallization process. The transition implies the formation of an intermediate band originated from the Ti deep levels.

Insulator-to-metal transition in heavily Ti-doped silicon thin film

Aligned amorphous and crystallized silicon nanorods (SiNRs) were successfully fabricated at low temperatures using radio frequency magnetron sputtering and hot wire chemical vapor deposition with glancing angle incident flux. The influences of the deposition pressure, sputtering power, substrate rotation and hydrogen dilution ratio on the diameter, density, orientation and crystallization of the Si nanorods were systematically investigated. With increasing sputtering power, the density of Si nanorods decreases and the diameter of SiNRs increases. The pressure has the opposite effect on the growth of SiNRs compared with the sputtering power. By combining glancing angle deposition (GLAD) with the hydrogen diluted silane in hot wire chemical vapor deposition (HWCVD), aligned crystallized Si nanorods with a crystalline volume fraction of 0.55 were achieved under a substrate temperature of 140 °C. The Si nanorods have been tested for photovoltaic application.

https://iopscience.iop.org/article/10.1088/0957-4484/20/27/275201/pdf

Aligned amorphous and microcrystalline Si nanorods by glancing angle deposition at low temperature

The hydrogen dilution profiling (HDP) technique has been developed to improve the quality and the crystalline uniformity in the growth direction of mu c-Si:H thin films prepared by hot-wire chemical-vapor deposition. The high H dilution in the initial growth stage reduces the amorphous transition layer from 30-50 to less than 10 nm. The uniformity of crystalline content X-c in the growth direction was much improved by the proper design of hydrogen dilution profiling which effectively controls the nonuniform transition region of Xc from 300 to less than 30 nm. Furthermore, the HDP approach restrains the formation of microvoids in mu c-Si: H thin films with a high Xc and enhances the compactness of the film. As a result the stability of mu c-Si: H thin films by HDP against the oxygen diffusion, as well as the electrical property, is much improved. (c) 2005 American Institute of Physics.

Meifang Zhu

Papers

Realization of radial p-n junction silicon nanowire solar cell based on low-temperature and shallow phosphorus doping.

Insulator-to-metal transition in heavily Ti-doped silicon thin film

Aligned amorphous and microcrystalline Si nanorods by glancing angle deposition at low temperature

The compact microcrystalline Si thin film with structure uniformity in the growth direction by hydrogen dilution profile

Nano-structure in micro-crystalline silicon thin films studied by small-angle X-ray scattering