Cu₂ZnSnSe₄ thin film solar cells produced via co‐evaporation and annealing including a SnSe₂ capping layer

Abstract

Cu 2 ZnSnSe 4 (CZTSe) thin film solar cells have been produced via co-evaporation followed by a high-temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe 2 capping layer has been evaporated onto the absorber prior to the high-temperature treatment. This eliminates the Sn losses due to SnSe evaporation. A solar cell efficiency of 5.1% could be achieved with this method. Moreover, the device does not suffer from high series resistance, and the dominant recombination pathway is situated in the absorber bulk. Finally, different illumination conditions (white light, red light, and yellow light) reveal a strong loss in fill factor if no carriers are generated in the CdS buffer layer. This effect, known as red-kink effect, has also been observed in the closely related Cu(In,Ga)Se 2 thin film solar cells.

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).…”

Investigation of selenization process of electrodeposited Cu–Zn–Sn precursor for Cu2ZnSnSe4 thin-film solar cells

“…Lower and higher energy peaks are attributed to the CZTSe and ZnSe emission, respectively. Note that, broad peak at 1.24 eV has been also observed by other authors [25][26][27]. They suggested that ZnSe which in our case was located at the CZTSe and Mo interface contained defects in the band gap caused by inclusion of Cu or Sn.…”

Multiple phases of Cu2ZnSnSe4 detected by room temperature photoluminescence

“…SnSe and SnSe 2 can be measured with Raman spectroscopy on our CZTSe solar cell absorbers under the same measurement conditions as shown in Ref. 18. Additionally, since our samples are grown in the Sn-poor composition range, Sn-selenides are not likely secondary phases.…”

“…[14][15][16] The presence of secondary phases in CZTSe can, to a certain extent be checked using Raman spectroscopy. 17,18 It is a tougher task to distinguish the different polymorphs. So far, only neutron scattering techniques can discern the different polymorphs of CZTS/ Se.…”