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Electrical and optical properties of thin film (n)CdSe/(p)CdTe heterojunction and its performance as a photovoltaic converter

MOTHURA N. BORAH1,* , S. CHALIHA2, P. C. SARMAH3, A. RAHMAN4

Affiliation

  1. Deptt. of Physics, D.R. College, Golaghat-785621, India
  2. Department of Physics, Bahona College, Jorhat-785101, India
  3. Electronics Division, Regional Research Laboratory, Jorhat-785006, India
  4. Deptt. of Physics, Gauhati University, Guwahati-781014, India

Abstract

Thin film (n)CdSe/(p)CdTe heterojunctions were fabricated by depositing p-type CdTe thin films on n-type CdSe thin films using the thermal evaporation technique, and their electrical and optical properties at room temperature as well as elevated temperatures have been investigated by current-voltage measurements. The different junction parameters such as diode ideality factors, barrier heights, Richardson constant, short-circuit currents, open circuit voltage, etc. were determined from I-V characteristics and found changing on vacuum annealing. The ideality factors (> 2 in dark at 303K) were found to decrease with increase in temperature. At room temperature (303K), the barrier height was found to be 0.7eV in dark and showed no temperature dependence in the range from 303K to 333K. The photovoltaic performance of the junction was found to improve on vacuum annealing. The structure with concentrations Na=2.43x1016/cm3 for CdTe and Nd= 9.03×1015/cm3 for CdSe showed a photovoltaic effect with fill factor 0.46, open-circuit voltage 135 mV, short-circuit current 2.06×10-4A/cm2 for an annealed sample and corresponding quantities 0.37, 148 mV, 1.9×10-4A/cm2 for an untreated sample. The fill factor was found to decrease with increase in temperature. The junctions exhibited spectral response within 550-900 nm giving a peak at wave length 762 nm. Proper doping and annealing lead to reduction of series resistance for achieving an ideal solar cell..

Keywords

Heterojunction, Annealing, Photovoltaic effect, Spectral response.

Submitted at: April 22, 2008
Accepted at: June 9, 2008

Citation

MOTHURA N. BORAH, S. CHALIHA, P. C. SARMAH, A. RAHMAN, Electrical and optical properties of thin film (n)CdSe/(p)CdTe heterojunction and its performance as a photovoltaic converter, Journal of Optoelectronics and Advanced Materials Vol. 10, Iss. 6, pp. 1333-1339 (2008)