P–N Junction Passivation in Kesterite Solar Cells by Use of Solution-Processed TiO2 Layer

Samaneh Ranjbar,Guy Brammertz,Siddhartha Garud,Afshin Hadipour,Maria Batuk,Marc Meuris,Joke Hadermann,Bart Vermang,Antonio F Da Cunha,Sylvester Sahayaraj,Jef Poortmans

doi:10.1109/jphotov.2017.2692208

Abstract

In this work, we used a solution-processed TiO2 layer between Cu2ZnSnSe4 and CdS buffer layer to reduce the recombination at the p–n junction. Introducing the TiO2 layer showed a positive impact on V OC but fill factor and efficiency decreased. Using a KCN treatment, we could create openings in the TiO2 layer, as confirmed by transmission electron microscopy measurements. Formation of these openings in the TiO2 layer led to the improvement of the short-circuit current, fill factor, and the efficiency of the modified solar cells.

Highlights

K ESTERITE Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are being investigated as a cost effective alternative for highly efficient Cu(In,Ga)(S,Se)2 (CIGS) solar cells
A few studies already reported on the passivation of kesterite solar cells by introducing atomic layer deposited (ALD)-coated TiO2 and Al2O3 layers between the kesterite absorber layer and CdS buffer layer
This kink anomaly that severely degrades the fill factor (FF) might be attributed to a high barrier at the conduction band

Summary

INTRODUCTION

K ESTERITE Cu2ZnSn(S,Se) (CZTSSe) solar cells are being investigated as a cost effective alternative for highly efficient Cu(In,Ga)(S,Se) (CIGS) solar cells. Based on this study a negative offset, called cliff-like band alignment, in which the conduction band of the buffer layer is lower than the one of the absorber layer decreases VOC in CIGS/CdS solar cells. This negative offset is a barrier for injected electrons under forward bias that leads to accumulation of injected electrons and increasing the recombination. Wu et al introduced an atomic layer deposited (ALD) TiO2 layer between a CZTSSe absorber and CdS buffer layer that improved VOC while short-circuit current (JSC ) and fill factor (FF) were similar to the unpassivated solar cells. Techniques such as e-beam lithography [12], [22] have been used to create the nanosized openings through the passivation layers

EXPERIMENTAL

Characterization of CZTSe Solar Cells With Modified p–n Junction

Electrical Analysis of CZTSe Solar Cells With Modified p–n Junction

CONCLUSION