Amorphous Zn(O,Se) buffer layer for Cu(In,Ga)Se2 thin film solar cells

Abstract

Amorphous Zn(O,Se) was used as a buffer layer with Cu(In,Ga)Se2 absorber in thin film solar cells. The complete device was fabricated using vacuum technique only, and no wet method was involved. The solar cells parameters were investigated with a change in the thickness of the buffer layer from 100 to 300 nm. In addition, the performance of the fabricated solar cells was compared to that of a reference solar cell, using CdS as a buffer layer on Cu(In,Ga)Se2. The preliminary results of this Cd-free solar cells showed a reasonable device performance. Also, the parasitic absorption in the blue region for the Cu(In,Ga)Se2/Zn(O,Se) device has been reduced, due to high transparency and high optical band gap of amorphous Zn(O,Se) buffer. Moreover, the Zn(O,Se) is relatively less toxic than the CdS buffer layer. Thus, the parasitic absorption in the 350–550 nm range and the toxicity raised from using CdS as a buffer layer have been overcome. Furthermore, open circuit voltage, short circuit current and an overall photoconversion efficiency of the device were enhanced to 454 mV and 27.1 mA/cm2 and 5.0% respectively with decreasing the thickness of amorphous Zn(O,Se) buffer layer to 100 nm.