Detecting ZnSe secondary phase in Cu2ZnSnSe4 by room temperature photoluminescence

Abstract

Secondary phases, such as ZnSe, occur in Cu2ZnSnSe4 and can be detrimental to the resulting solar cell performance. Therefore, it is important to have simple tools to detect them. We introduce subband gap defect excitation room temperature photoluminescence of ZnSe as a practical and non-destructive method to discern the ZnSe secondary phase in the solar cell absorber. The PL is excited by the green emission of an Ar ion laser and is detected in the energy range of 1.2–1.3 eV. A clear spatial correlation with the ZnSe Raman signal confirms this attribution.

Optical properties of Cu_2ZnSnSe_4 thin films and identification of secondary phases by spectroscopic ellipsometry

“…The slight differences between the PL peak positions can occur due to different compositions, which may lead to different tailing properties and other dominating defects. The PL spectra from the backside of each absorber show additionally a broad peak at around 1.2 eV, known as a ZnSe defect transition in literature [30,[33][34][35]. These results are in good agreement with SE and Raman results: All samples show clear evidence for the existence of ZnSe secondary phases at the back side of the absorber for both SE and Raman spectroscopy (see Table 1 and Section 3.2).…”

“…The Raman signal from ZnSe secondary phases in CZTSe is strongly enhanced due to the resonant Raman effect for the 457.9nm laser, as the energy of its photons is in the region of the band gap energy of ZnSe (~2.7 eV). Hence, even very small ZnSe fractions in the sample can be identified with the "blue" excitation laser [10,30]. The utilization of solely the 532 nm excitation can only reveal very large amounts of ZnSe in the sample.…”

Cu‐Rich Precursors Improve Kesterite Solar Cells

“…This transition has been previously attributed to a defect related transition in ZnSe, due to resonant defect excitation. [ 17,18 ] This ZnSe emission increases towards the back of the absorber. ZnSe has been previously related with the series resistance of the solar cells, [ 2 ] however, using micro PL we are not able to range from 25° to 55° can be seen in the Supporting Information Figure S1).…”

Interference effects in photoluminescence spectra of Cu2ZnSnS4 and Cu(In,Ga)Se2 thin films

“…As an example, ZnSe is a secondary phase commonly present in CZTSe, resulting in characteristic features in the PL spectrum. 9 In the present paper, another phenomenon affecting the PL spectrum is demonstrated, namely, that of thin film interference. This effect follows from the coherent superposition of the luminescence emitted and internally reflected by the sample.…”