研究目的
To investigate the impact of the TCO substrates on the CZTSe growth, the reactions at the back contact and the electrical properties of solar cells.
研究成果
CZTSe based solar cells deposited on Mo, ZnO:Al (AZO), and SnO2:F (FTO) coated substrate have been studied. It has been found that the annealing temperature under Se has no impact on the FTO substrate up to 600°C, whereas the temperature should remain below 500°C for the 1300-nm-thick AZO. During the CZTSe deposition, FTO substrate is the most stable: no reaction are thermodynamically favored between the CZTSe phases and FTO. However, CZTSe decomposition reaction is thermodynamically possible at the ZnO interface with the formation of a ZnSe phase. Moreover both FTO and AZO layer hinder the Na diffusion from the glass to the CZTSe absorbers leading to a lack of Na compared to the standard Mo substrate. Thus Solar cells based on CZTSe were made with an efficiency of 2.3% on FTO while solar cells CZTSe deposited on Mo up to 8.0%.
研究不足
The low efficiency of CZTSe solar cell on FTO coated substrate suffers of recombination at the back contact which limits Voc, Jsc and FF. Low efficiency has been explained by the presence of the ZnO secondary phase at the back contact and the low diffusion of Na through CZTSe.
1：Experimental Design and Method Selection:
Thin Cu-Zn-Sn precursors were deposited on Mo, SnO2:F (FTO) and ZnO:Al (AZO) coated soda lime glass substrates using RF magnetron co-sputtering from Cu, Zn and Sn targets at room temperature. These films were then annealed inside a graphite box under a pure selenium atmosphere.
2：Sample Selection and Data Sources:
The composition of the absorber has been studied by Glow discharge optical spectroscopy (GD-OES) measurements. The crystallinity of the absorbers was examined by X-ray diffraction (XRD). Raman microprobe measurements were conducted using a HR800-UV Horiba Jobin Yvon spectrometer.
3：List of Experimental Equipment and Materials:
RF magnetron co-sputtering system, graphite box, selenium pellets, GD-OES, XRD, Raman spectrometer, SEM.
4：Experimental Procedures and Operational Workflow:
After annealing, a layer of 50 nm of CdS was deposited on the CZTSe absorber by chemical bath deposition and a double layer of ZnO:i / AZO of around 350 nm was deposited by sputtering to complete the solar cell.
5：Data Analysis Methods:
The electrical properties of the solar cells were characterized by current voltage measurements in dark and light illumination at 25°C (AM1.5 global spectrum). Quantum efficiencies were collected using Oriel IQE-200 instruments.
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