CdTe Photovoltaic Cell Research at CSM

Researchers at the Colorado School of Mines have been working with CdTe photovoltaic cells since the early 1990's. In that time, we have acquired considerable expertise and equipment for cell fabrication and characterization. Our research is conducted under the auspices of CSM's Center for Solar and Electronic Materials.

Researchers

Tim Ohno. Tim is an academic faculty member of the Physics Department. His research specialties are surface characterization techniques and CdTe cell characterization techniques.

Reuben Collins. Reuben is an academic faculty member of the Physics Department. His research specialties are optoelectronic characterization of semiconductors and near-field scanning optical microscopy.

Victor Kaydanov. Victor is a research faculty member of the Physics Department. His research specialties are electronic characterization of semiconductor films and photovoltiac devices.

Fred Seymour. Fred is a post-doctoral fellow in the Physics Department. His research specialties are the electronic characterization of photovoltiac cells, particularly with capacitance transients and admittance spectroscopy.

Joe Beach. Joe is a research faculty member of the Physics Department. His research specialties are thin film and photovoltaic cell growth and characterization.

Fabrication Facilities

The Center for Solar and Electronic Materials and the CdTe Photovoltaics Research Group together have the equipment to make CdTe-based photovoltaic cells starting from either bare glass or commercially produced tin oxide coated glass. Available processes include:

• Indium tin oxide grown by sputtering.
• CdS grown by thermal evaporation or chemical bath deposition.
• CdTe grown by thermal evaporation or gas jet deposition.
• CdCl₂ treatments performed using aqeuous solutions, thermal evaporations, or vapor sources.
• Anneals performed in tube furnaces with controlled atmospheres.
• ZnTe:Cu back contact layers grown by thermal evaporation, with the ZnTe and Cu being deposited either in sequence or simultaneously.
• Metalization grown by Au evaporation or Ti sputtering.
• Cell isolation performed by manual scribing or photolithographic techniques.

Characterization Facilities

The Center for Solar and Electronic Materials and the CdTe Photovoltaics Research Group together have the equipment for a broad range of film and cell characterizations. Available measurements include:

• Film thickness using surface profilometry.
• Surface characterization using atomic force microscopy and Auger electron spectroscopy.
• Structural characterization using x-ray diffraction and scanning electron microscopy.
• Optical characterization using transmission, reflection, photoluminescence, electroluminescence, and ellipsometry. 
• Electronic characterization using Hall measurements, dark and light current-voltage measurements, capacitance measurements, admittance spectroscopy, capacitance transients, and quantum efficiency measurements.
• Device degradation using controlled temperature and illumination.

Graduate Student Theses

The following theses have been written by CSM graduate students investigating CdTe photovoltaic cells.

• "Effects of Post-Deposition Heat-Treatment on Morphology and Microstructure of CdTe Grown by Electrodeposition", Bin Qi, M.S, Physics.
• "Electrodeposition of Cu-doped Zinc Telluride as a p-Type Back Contact Layer for Cadmium Sulfide/Cadmium Telluride Solar Cells", Jason Selby, M.S., Materials Science.
  
• "Characterization of Electrodeposited CdTe Prepared Under Different Conditions", Esam Alarfaj, M.S., Physics.
  
• "Polycrystalline CdS Thin Films Deposited by Chemical Bath Deposition", Yuming Zhu, Ph.D., Applied Physics.
  
• "Study of Back Contact Formation on CdTe/CdS Thin Film Solar Cells", Jian Tang, Ph.D., Applied Physics.
  
• "Development of High Efficiency Polycrystalline CdTe/CdS Solar Cells Using Electrodeposition", Wenjie Song, Ph.D., Applied Physics.
  
• "An Investigation into Degradation of CdTe Solar Cells", Donald T. Morgan, M.S., Materials Science.
• "Electrical and Optical  Properties of Bias Stressed CdTe Solar Cells", Scott Townsend, Ph.D., Applied Physics.
• "Studies of the Basic Electronic Properties of CdTe Thin Films and CdTe/CdS Solar Cells", Angelo S. Gilmore, Ph.D., Applied Physics.
• "Development and Analysis of Vapor Transport Deposition of Cadmium Telluride Thin Films", James M. Kestner, Ph.D., Materials Science.
• "Fundamental Electro-Optical Studies of CdTe Solar Cells", Scott Feldman, Ph.D., Applied Physics.
• "Studies of Electronic States Controlling the Performance of CdTe Solar Cells", Fred Seymour, Ph.D., Materials Science.