A Study on the Effects of Selenization Temperature on the Properties of Na-Doped Cu2ZnSn(S,Se)4 Thin Film and Its Correlation with the Performance of Solar Cells.

Zhanwu Wang,Dongyue Jiang,Fancong Zeng,Yingrui Sui

doi:10.3390/nano11092434

Abstract

In this study, we prepared Na-doped Cu2ZnSn(S,Se)4 [noted as (Na0.1Cu0.9)2ZnSn(S,Se)4] films on the Mo substrate using a simple and cheap sol–gel method together with the post-annealing technique. The effects of selenization temperature on the properties of Na-doped Cu2ZnSn(S,Se)4 were surveyed. The results indicated that some sulfur atoms in the films were substituted by selenium atoms by increasing the selenization temperature, and all films selenized at different temperatures had a kesterite structure. As the selenization temperature increased from 520 to 560 °C, the band gaps of the film can be tuned from 1.03 to 1 eV. The film with better morphology and opto-electrical properties can be obtained at an intermediate selenization temperature range (e.g., 540 °C), which had the lowest resistivity of 47.7 Ω cm, Hall mobility of 4.63 × 10−1 cm2/Vs, and carrier concentration of 2.93 × 1017 cm−3. Finally, the best power conversion efficiency (PCE) of 4.82% was achieved with an open circuit voltage (Voc) of 338 mV, a short circuit current density (Jsc) of 27.16 mA/cm2 and a fill factor (FF) of 52.59% when the selenization temperature was 540 °C.

Highlights

Cu2 ZnSn(S,Se)4 (CZTSSe) is a helpful absorber layer for high reserves and inexpensive thin film solar cells because of its appropriate semiconductor characteristics having a tunable band gap, p-type conduction characteristics, and high absorption coefficient [1,2,3].it can be considered as a substitute to Cu(In, Ga)Se2 and CuInS2 absorbers, in which the extremely rare and expensive indium (In) is substituted by abundant and environmentally friendly zinc (Zn) and tin (Sn) [4,5,6]
There are several factors impeding the efficiency of further improvement for CZTSSe solar cells, including the crystal quality and optoelectronic properties of the CZTSSe semiconductors, as well as the energy band matching between the CZTSSe and CdS interface [10,11,12,13]
Recent research has shown that the fabrication of adjustable band gap absorbers is a practical way to solve the band matching of CdS and CZTSSe heterojunction interfaces and improve cell efficiency

Summary

Introduction

Cu2 ZnSn(S,Se) (CZTSSe) is a helpful absorber layer for high reserves and inexpensive thin film solar cells because of its appropriate semiconductor characteristics having a tunable band gap, p-type conduction characteristics, and high absorption coefficient [1,2,3]. It can be considered as a substitute to Cu(In, Ga)Se2 and CuInS2 absorbers, in which the extremely rare and expensive indium (In) is substituted by abundant and environmentally friendly zinc (Zn) and tin (Sn) [4,5,6]. Cu2 ZnSn(S,Se) as well as the device performance have been investigated in detail

Experimental Details

Device Fabrication

Characterization

Results and Discussion

Conclusions