[13a-A202-1~12] 13.9 Compound solar cells

▼ [13a-A202-11] Application of grading Se alloys for high efficiency CdTe solar cells

〇(DC)CHUANG LI¹, Wei Fu², Hamidou TANGARA², Chuanqi Li¹, Jingquan Zhang¹, Takeaki Sakurai² (1.Sichuan University, 2.University of Tsukuba)

Keywords:CdTe solar cell, Se alloys

Improving the efficiency of CdTe solar cells will further promote the cost-reduction of photovoltaics. For devices with CdS as the buffer layer, very thin CdS layer can greatly deteriorate the performance, on the account of the deficit open circuit voltage (Voc) and fill factor (FF). However, the CdS layer is always considered as “dead” layer, which indicated that the photons absorbed by the CdS layer cannot be converted into photocurrent. Thick CdS layer will significantly reduce the current collection at the short wavelength region (300-520nm). In this work, for optimal cell performance, 70nm CdSe was composited with a very thin CdS layer (40nm) as the buffer layer with the same application of CdTe deposition, post-annealing process, back contact (ZnTe:Cu) and back electrode (Au). The highest efficiency reached 17.38%, with Voc 823mV, Jsc 28.67mA/cm², which is the highest among CdTe solar cells with the CdS/CdSe composited window layer.
Defect distribution revealed by admittance spectroscopy was used to analyze the recombination in the devices. Introducing the Se alloys would reduce the density of the deep defect with activation energy about 0.50eV, which may relate to the complex. The reduced deep defect may be the reason for efficiency enhancement. The device with Se alloys also exhibits higher photoluminescence intensity in the buffer/absorber interface with peak redshift, indicating less nonradiative recombination and the formation of the Se alloys. The less defective Se alloys in the vicinity of the interface may be the reason for the efficiency enhancement.