A review on solar cells from Si-single crystals to porous materials and quantum dots

Abstract

Solar energy conversion to electricity through photovoltaics or to useful fuel through photoelectrochemical cells was still a main task for research groups and developments sectors. In this article we are reviewing the development of the different generations of solar cells. The fabrication of solar cells has passed through a large number of improvement steps considering the technological and economic aspects. The first generation solar cells were based on Si wafers, mainly single crystals. Permanent researches on cost reduction and improved solar cell efficiency have led to the marketing of solar modules having 12-16% solar conversion efficiency. Application of polycrystalline Si and other forms of Si have reduced the cost but on the expense of the solar conversion efficiency. The second generation solar cells were based on thin film technology. Thin films of amorphous Si, CIS (copper-indium-selenide) and t-Si were employed. Solar conversion efficiencies of about 12% have been achieved with a remarkable cost reduction. The third generation solar cells are based on nano-crystals and nano-porous materials. An advanced photovoltaic cell, originally developed for satellites with solar conversion efficiency of 37.3%, based on concentration of the solar spectrum up to 400 suns was developed. It is based on extremely thin concentration cells. New sensitizer or semiconductor systems are necessary to broaden the photo-response in solar spectrum. Hybrids of solar and conventional devices may provide an interim benefit in seeking economically valuable devices. New quantum dot solar cells based on CdSe-TiO2 architecture have been developed.

Keywords: Nanotechnology; Porous Si; Quantum dots; Solar cells; Solar energy conversion.

Graphical abstract

Fig. 1

Solar system based on Si-single crystals.

Fig. 2

Second generation solar cells, based on thin film.

Fig. 3A

Field-emission scanning electron microscopy (FESEM) images of (a) TiO₂ nanorod array (top view), (b) cross-sectional SEM image of TiO₂ nanorod array grown on FTO (fluorinated tin oxide), (c) top view and (d) cross-sectional of CdS Quantum Dot’s (QDs) coated TiO₂ nanorod array.

Fig. 3B

CdS QDs coated TiO₂ nanorods: (a), (b) and (c) TEM (Tunneling electron microscope) image under different magnification. (d) HRTEM image.

Fig. 4

Quantum dot representation.

Fig. 5

Quantum dot layer (SEM).

Fig. 6

Diagram of a nano-solar cell.

Fig. 7

Charge-transfer processes between CdS and TiO₂ in a QD/nanowire based solar cell.

Fig. 8

The progress of research on porous Si.

Fig. 9

The chemical etching cell.

Fig. 10

SEM plane view of a Ag loaded p- type (100) Si surface (a) and the porous Si layer produced by HF (40%), H₂O₂(35%) and (H₂O) by volume (25/15/4) after 3 s (b), 10 s (c), and 15 s (d).

Fig. 11

SEM of p-Si in different solutions for different time intervals (a) SEM – p-Si etched in 22 M HF-0.05 M KIO₃ for 1 h, (b) SEM – p-Si etched in 22 M HF-0.05 M KBrO₃ for 1 h, (c) p-Si etched in 22 M HF-0.1 M K₂Cr₂O₇ for 1 h, (d) p-Si etched in 22 M HF – 0.05 M K₂Cr₂O₇ for 1 h, (e) SEM- p-Si etched in 27 M HF – 0.05 M K₂Cr₂O₇ for 1 h, (f) p-Si etched in 22 M HF – 0.05 M K₂Cr₂O₇ for 3 h.