Performance improvement of solution-processed CdS/CdTe solar cells with a thin compact TiO2 buffer layer

Abstract

The device performance of CdS/CdTe solar cells largely depends on not only the back ohmic contact, but also the conformality of CdS window layer coating. In order to reduce the light absorption loss in CdS, the CdS thickness is usually less than 100nm. However, pinholes in CdS and non-conformal coverage of CdS on transparent conducting oxide layer will cause shunting thus leading to device performance degradation and failure. In this paper, low-temperature and low-cost fabrication methods, i.e., chemical bath deposition and electrochemical deposition, were used to deposit CdS and CdTe, respectively. It was found that the yield of device was around 20% due to shunting. In order to alleviate this problem, a compact layer of TiO2 was inserted between the fluorine-doped tin oxide and CdS as a buffer layer. The thickness effect of TiO2 was studied and showed that devices with thin (20nm thickness) TiO2 performed better than the counterparts with thick layers. It was discovered that device yield improved to 80% and stability in air substantially improved with TiO2 layer.