ZnO back reflector prepared by MOCVD technique for flexible solar cell applications

We have prepared ZnO films by MOCVD technique and applied them as a back reflector in flexible thin film silicon solar cells. The gas mixture of diethylzinc and water was used as reactant gas while diborane was employed as a doping gas. We found that the MOCVD ZnO films had a tetrapodlike morphology and their properties strongly depended on substrate temperature. When the substrate temperature increased, their grain size tended to become larger while the resistivity of the films gradually decreased. At the same substrate temperature set-point, the ZnO films grown on polyimide showed larger gain size and lower resistivity than the films grown on glass substrates. Single junction n-i-p amorphous silicon solar cells using polyimide film as a substrate were fabricated in order to estimate the effects of the MOCVD ZnO back reflector. Experimental results indicated that the MOCVD ZnO back reflector was effective in improving solar cell performance, mainly owing to an increase in Jsc. The highest cell efficiency of 6.1% was achieved at the ZnO back reflector thickness of about 2000 nm (cell active area 2.50 cm2).

► Naturally texture surface grown ZnO films by MOCVD technique.
► Application to flexible substrate.
► No use of post-treatment to modify surface of ZnO back reflector.