Annealing behavior of reactively sputtered precursor films for Cu2ZnSnS4 solar cells

Abstract

Reactively sputtered Cu-Zn-Sn-S precursor films are prepared and recrystallized by rapid thermal processing to generate Cu 2 ZnSnS 4 solar cell absorber layers. We study how the film properties are affected by substrate heating and composition. The stress, density and texture in the films were measured. Compressive stress was observed for the precursors but did not correlate to the deposition temperature, and had no influence on the properties of the annealed films or solar cells. However, the substrate temperature during precursor deposition had a large effect on the behaviour during annealing and on the solar cell performance. The films deposited at room temperature had, after annealing, smaller grains and cracks, and gave shunted devices. Cracking is suggested to be due to a slightly higher sulfur content, lower density or to minor differences in material quality. The grain size in the annealed films seems to increase with higher copper content and higher precursor deposition temperature. The best device in the current series gave an efficiency of 4.5 %.

Point defects, compositional fluctuations, and secondary phases in non-stoichiometric kesterites

“…Because of this disorder the term 'disordered kesterite' has arisen [6]. depending on the synthesis parameters, especially the annealing temperature [7]. The first hint of a temperature dependent change in the cation arrangement within the kesterite-type structure was observed in CZTS by in situ synchrotron x-ray diffraction (XRD) [8].…”

Effect of calcination temperature on the properties of CZTS absorber layer prepared by RF sputtering for solar cell applications

“…Secondary phases may remain in the film after heat treatment. Ericson et al [20] obtained highly crystalline CZTS films after annealing in H 2 S atmosphere. Surgina et al [21] have also studied the annealing effect on structural and optical properties of CZTS films grown by pulsed laser deposition in N 2 atmosphere.…”

Influence of the Cu2ZnSnS4 absorber thickness on thin film solar cells

“…Figure shows the efficiency (>4%) of CZTS solar cells from some reported data in the literature since 2008 as a function of absorber thickness. The data are grouped according to composition, expressed as the Zn/Sn ratio . There is no obvious correlation between device efficiency and absorber thickness; however, it is supposed that any trends that might emerge are in fact hidden by (a) the compositional dependence of solar cell efficiency and the diversity in compositional measurement techniques and calibration methods used and (b) the great variation of methods used to prepare the CZTS absorbers.…”

“…Reported efficiencies of Cu 2 ZnSnS 4 (CZTS) solar cells from PVD deposition as function of absorber thickness grouped by Zn/Sn . The world record 9.2% device is not included as thickness was not reported.…”