A Study towards the Possibility of Ultra Thin CdS/CdTe High Efficiency Solar Cells from Numerical Analysis

摘要

Polycrystalline cadmium telluride (CdTe) is the leading material for realization of low cost and high efficiency solar cell for terrestrial use. In this work, a conventional structure of CdTe thin film solar cells [1] was investigated and conversion efficiency as high as 13.2% was achieved with the CdTe baseline structure of SnO_2/CdS/CdTe. To explore the possibility of ultra thin and high efficiency CdS/CdTe solar cells, the CdTe absorber layer and CdS window layer were decreased to the extreme limit and 1 μm thin CdTe layer is found to show reasonable range of efficiency with stability. Moreover, it was found that there were scopes to increase cell efficiency by reducing the cadmium sulfide (CdS) window layer thickness. The CdS window layer was reduced to 60 nm together with the insertion of zinc oxide (ZnO) or zinc stannate (Zn_2SnO_4) as the buffer layer to prevent forward leakage current. All the simulations have been done using Analysis of Microelectronic and Photonic Structures (AMPS 1D) simulator. The maximum conversion efficiency of 18.3% (Voc = 1.00 V, Jsc = 26.15 mA/cm~2, FF = 0.769) was achieved with 1 μm-CdTe absorber layer, 60 nm-CdS window layer and 100 nm of ZnO or Zn_2SnO_4 buffer layer. Furthermore, it was found that the cell normalized efficiency linearly decreased with the increasing operating temperature at the gradient of -0.4%/℃, which indicated better stability of the CdS/CdTe solar cells.