研究目的
To identify the factors related to technological processes which affect the magnitude of persistent photoconductivity (PPC) in thin Cu(In,Ga)Se2 films and to evaluate the concentration of metastable defects.
研究成果
The concentration of metastable defects exceeds in typical samples 1017 cm-3 and does not depend on CGI value in the range of 0.78-0.99. Annealing in selenium works well for their reduction only in case of the sodium free samples. The detailed analysis of the impact of sodium (and other alkalis) on metastable behavior is still to be performed.
研究不足
The presence of potential barriers at grain boundaries in sodium-free samples might distort the quantitative results both for thin films via reduced mobility and for solar cells through Fermi-level pinning by defects at the grains.
1：Experimental Design and Method Selection:
The study discusses PPC within a model of relaxing defects acting as donors or acceptors depending on their configurational and charge state.
2：Sample Selection and Data Sources:
Samples were fabricated in various laboratories with various treatments/processes, having average Ga/In ratio around
3：List of Experimental Equipment and Materials:
Samples were
4：8-2 μm thick, with Au or Ni/Al/Ni electrodes in planar configuration. Conductivity and PPC were monitored using a Keithley 101 current amplifier. Experimental Procedures and Operational Workflow:
Experiments were carried out in 100-330 K temperature range. Thermal equilibrium state was achieved by heating the sample above room temperature. The metastable state of PPC was created by illumination for 30 min at room temperature and cooling under illumination.
5：Data Analysis Methods:
The position of the Fermi level above the valence band was calculated by using thermal equilibrium conductivity measured at 300 K.
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