A Study Of Flexible A-Si:H Thin-film Solar Cells Based On Plasmonic Structure

Energy supply problem and ecological consideration in the world have taken over as main driving forces in promoting alternative energy sources, especially photovoltaic solar energy. And the key measures to promote the application of solar cell are to reduce the cost and improve the energy conversion efficiency. Flexible hydrogenated amorphous silicon (a-Si:H) thin-film solar cell (FATFSC) has wide application as being light-weight, prehensile and portable. However, a-Si:H thin-film solar cells (ATFSC) have a disadvantage of low efficiency at the same time due to the ultrathin absorption layer. So it needs to optimize the process parameter or fabricate some novel plasmanic structure to enhance the light absorption of a-Si:H thin film and improve the efficiency of ATFSC.Firstly, the effect of O2 concentration (0.19%,0.21%,0.23% and 0.26%) on the thickness, resistivity and transmittance of front contact ITO were studied. It was demonstrated that the O2 concentration had a great effect on the electrical performance of ITO film. And the ITO film has the smallest resistivity with O2 concentration of 0.21%. Then ATFSCs were fabricated with the ITO film prepared with the four concentrations of O2, and the 0.21% one had the best conversion efficiency. Thus, the optimal O2 concentration was achieved.Secondly, based on the self-assembly of anodic alumina oxide membranes, the Al substrates with periodic semi-spherical nanodents (pitch:350 nm,500 nm) were achieved. It was demonstrated that the nanodent structure had obviously improved the optical absorption of ATFSC at the whole absorption wavelength. And the optical simulation, a method of finite-differential time-domain (FDTD) simulation, was applied to verify the light-trapping effect of nanodent structure at the same time. As a result, the short-circuit current density and energy conversion efficiency of ATFSCs with this novel nanodent structure were eventually improved by 29.4% and 30.8%, respectively, which is even better than solar cells on FTO glass with random structure, owing to that the nanodent light-trapping structure in ATFSC motivates the surface plasmon resonances (SPR) effect and the waveguide modes. In addition, the performance of ATFSC fabricated on nanodent Al substrate with a pitch of 500 nm is better than that of 350 nm.Thirdly, by using the simple, convenient and efficient anodization method, a compact layer of Al2O3 film was obtained on the surface of Al substrate. It can act as an efficient role of barrier to restrain the diffusion between Ag film and Al substrate. And ATFSC with compact Al2O3 indeed improved the energy conversion efficiency by 3.4%. Furthermore, thisdiffusion barrier can really prevent the ATFSC from being damaged at serious condition such as high temperature.Finally, ATFSC fabricated on nanodent Al substrate was encapsulated by PDMS and tested at different bending angle and oblique incidence angle. It demonstrated excellent flexibility while the FATFSC maintained 92.4% of initial efficiency even at a bending angle of 120 degree. And it can also hold 60.7% of initial efficiency at an oblique incidence of 60 degree, which indicated that the a-Si:H thin-film solar cells based on nanodent structure really achieved an outstanding light-trapping effect in wide incident angles.