CuSCN as the Back Contact for Efficient ZMO/CdTe Solar Cells.

Deng-Bing Li,Michael J Heben,Adam B Phillips,Randy J Ellingson,Demilt Rhiannon,Yanfa Yan,Rasha A Awni,Fadhil K Alfadhili,Niraj Shrestha,Feng Yan,Sandip S Bista,Zhaoning Song

doi:10.3390/ma13081991

Abstract

The replacement of traditional CdS with zinc magnesium oxide (ZMO) has been demonstrated as being helpful to boost power conversion efficiency of cadmium telluride (CdTe) solar cells to over 18%, due to the reduced interface recombination and parasitic light absorption by the buffer layer. However, due to the atmosphere sensitivity of ZMO film, the post treatments of ZMO/CdTe stacks, including CdCl2 treatment, back contact deposition, etc., which are critical for high-performance CdTe solar cells became crucial challenges. To realize the full potential of the ZMO buffer layer, plenty of investigations need to be accomplished. Here, copper thiocyanate (CuSCN) is demonstrated to be a suitable back-contact material with multi-advantages for ZMO/CdTe solar cells. Particularly, ammonium hydroxide as the solvent for CuSCN deposition shows no detrimental impact on the ZMO layer during the post heat treatment. The post annealing temperature as well as the thickness of CuSCN films are investigated. Finally, a champion power conversion efficiency of 16.7% is achieved with an open-circuit voltage of 0.857 V, a short-circuit current density of 26.2 mA/cm2, and a fill factor of 74.0%.

Highlights

In the past few years, cadmium telluride (CdTe) solar cells have experienced a rapid performance improvement, with certified record power conversion efficiencies (PCEs) reaching 22.1% for cells and over 18.6% for modules [1,2]
The valence band offset between CdTe and CuSCN is favorable for the holes to be extracted from the CdTe layer
Atomic force microscopy (AFM) measurements were performed to confirm the uniformity of CuSCN film deposited on the CdTe films

Summary

Introduction

In the past few years, cadmium telluride (CdTe) solar cells have experienced a rapid performance improvement, with certified record power conversion efficiencies (PCEs) reaching 22.1% for cells and over 18.6% for modules [1,2]. The efficiency loss is mainly caused by the low p-type conductivity and high electron affinity of CdTe films [4,5], which make them crucial challenges to form a good ohmic contact between CdTe and a metal electrode. The existence of non-ohmic contact produces a back barrier and increases the recombination at the interface of CdTe and the metal electrode, significantly. Materials 2020, 13, 1991 limiting the open-circuit voltage (VOC ) and fill factor (FF) of CdTe solar cells. To overcome this issue, copper (Cu) is commonly used to improve the conductivity of CdTe and reduce the back-barrier height

Methods

Results

Conclusion