Design and Fabrication of the Thin-Film InGaN Solar Cells with Diffraction Gratings

With the increasing growth in economics, the oil price has gone up continuously in recent years. In addition to reduce the natural resources, the fossil fuel burn will produce a great deal of CO2 and thus the world’s weather will be influenced apparently by the green house effect. Attempt to solve these problems can be done by the use of green energy technique that gives rise to the progress of the solar cell engineering becomes quickly. Compared with the other material systems, the InGaN-based alloys are promising for the photovoltaic applications since they have the unique features including direct band gap, high drift velocity of charged carriers, and high radiation tolerance. Besides, the available photoresponse could be approach to the full solar spectrum for the tandem cells consisted of various In contents to obtain the multiple absorption band gaps. In this project, we will dedicate to exitaxial growth of InGaN solar cell by using MOCVD. In general, epitaxial growth of InGaN is challenging because InN tends to thermal decomposition at high temperature. Besides, there is a solid phase miscibility gap existed between InN and GaN. Therefore, it is difficult to achieve the good quality of the thick InGaN epilayer with high In content. In order to improve the device performances, solar cell with a doping gradient is made to induce a back surface field. Further, the sapphire substrate will be removed by using laser lift-off process and then a high reflectivity coating is performed on the backside of cell to reflect the unused photons toward the intrinsic absorption region. Finally, this thin-film solar cell is transferred to the substrate with high thermal conductivity for the purpose of reducing the thermal effect. Otherwise, the intrinsic absorption layer will be displaced by the quantum well structure with biaxial strain to increase the In content (＞20%) and to extend the absorption range. To data, researches associated with the integration of periodic diffraction gratings on Si solar cells have been extensively studied. Consequently, the diffraction optical elements (DOE) have shown the ability to improve the device efficiency significantly. However, there is almost no the report related to the influence of utilizing the DOE on InGaN solar cell. In this project, we will fabricate the DOE on top of the InGaN solar cell to increase the amount of the trapped lights and to suppress the outgoing zero-order wave as well. Experimentally, the diffraction grating with a given geometry will be designed carefully by FDTD software, and then the one-dimensional or two-dimensional periodic gratings are fabricated by holography or electron-beam lithography. It is expected that the quantum efficiency of solar cells with the DOE could be enhanced as compared to the device without it.

Project ID:PB9808-2385
External Project ID:NSC98-2221-E182-060