Effect of oxide thin films in back contact on the optical absorption efficiency of thin crystalline Si solar cells
- Effect of oxide thin films in back contact on the optical absorption efficiency of thin crystalline Si solar cells
- 변석용; 변석주; 이택성; 신동우; 김원목
- crystalline Si solar cells; back contact; Optical absorption efficiency; ZnO
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- Reduction of production cost is ever-demanding in photovoltaic industry. In crystalline Si solar cell, much effort has been given to develop crystalline Si solar cells with reduced thickness in order to achieve higher cost-effectiveness. For thin crystalline Si solar cells, maximizing the incorporation of the incoming light into the active layer is of great importance to maintain or even improve the conversion efficiency. One of the main activities for maximizing the light absorption is texturing and applying anti-reflection coating for the front surface, and the other is designing the back contact which enables minimizing losses at the back contact and redirecting the reflected light into Si by utilizing low index oxide layer such as ZnO thin films for total reflection mode at Si/oxide interface. In this study, the optical absorption efficiency of thin crystalline Si solar cells with back contact made of ZnO based oxide layer and metallic electrodes by using a direct absorption calculation algorithm which is based on the three-dimensional modeling and ray-tracing technique. As ZnO based oxide layers, undoped ZnO thin films fabricated both by normal magnetron sputtering and oblique incidence sputtering and Ga-doped ZnO layer with relatively high carrier concentration were prepared and their estimated optical constants were utilized in numerical analysis. The front surface was assumed to be either flat or Lambertian. The simulation results showed that the insertion of oxide layer could increase the absorption up to 6% when compared with only Al back contact, and that the refractive indices of oxide layers had marginal effect on the total absorption indicating the choice of oxide layer is more open from the optical point of view. More detailed analyses on optimum thickness of oxide layer depending on the oxide layer type will be discussed in this presentation.
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