Single Crystal CuSe - CdSe and CdSe-Zn_xCd_(1_x)Se Solar Cells

摘要

Heterojunction Cu Se-CdSe and CuSe-Zn_xCd_(1_x)Se (x < 0.4) devices have been prepared on orientated single crystal substrates by a Chemiplating technique. The single crystal CdSe and Zn Cd Se substracs were grown from the vapour phase in this laboratory. The structure of the Cu Se layers was investigated using Reflection High Energy Diffraction (RHEED) and found to take the cubic modification. in the case of the CdSe substrates, the layer thickness has been found to follow an equation related to t, where t, is the chemiplating time. The current-voltage characteristics of all devices showed good rectifying characteristics except for heterojunctions formed on very low resistivity (=0.2Ωcm) CdSe substrates, where a short heat treatment of 2 minutes in air of 30 minutes in nitrogen was found to be necessary. The photovoltaic output characteristics have been measured under simulated AM1 illumination. Cells formed on CdSe were found to have higher short circuit current densities (Jsc and lower open circuit voltages (Voc) than those produced on the mixed Zn Cd Se crystal substrates. Typical values of Voc and Jsc were 200 m Voc and 3.8 mA/cm~2 for CdSe based devices and 420 m Voc and 1.0 mA/cm~2 for cells formed on for example Zn_xCd_(1-x)Se (x = 0.4). The spectral dependence of V was measured for the devices, and showed that the principal response arose from the Cu Se in most cases Photo capacitance spectra were also measured and used to identify the more important deep levels. The main threshold in all the devices indicated a dominant level with an activation energy of between 1.0 and 1.1 e V with respect to the conduction band in the CdSe or Zn_xCd_(1-x)Se respectively.