Radiation effects on fabricated Cu2S/CdS heterojunction photovoltaic cells

The photovoltaic properties including I-ri characteristics. junction capaci tance (C-V), short-circuit current (I-sc), open-circuit voltage (V-oc), fil l factor (ff), efficiency (eta) and spectral response of Cu2S/CdS heterojun ction cells have been examined before and after exposure to nuclear radiati on. This included gamma -rays of Co-60, and electron beams (at 1.5 MeV ener gy). The short-circuit current (I-sc) decreased, while the open-circuit voltage (V-oc), the fill factor (ff) and the efficiency (eta) increased after heat treatment (at 260 degreesC in air for 20 min). The I-sc effect during expos ure to gamma -rays was studied. It was found that I-sc increases as the dos e rate increases. The sensitivity dependence of the I-sc density on dose ra te was observed to be linear, and hence a universal constant for its sensit ivity is found to be 45 (nA/cm(2)) (rad/s). No permanent damage was shown until about 300 Mrad for gamma rays and 380 M rad for electron beams. After these doses, the I-sc and V-oc slightly decre ased on increasing the absorbed dose. After heat treatment, the spectral response was modulated. It was found tha t the wavelength response against the photocurrent decreased from 1000 to 8 00 nm and the photocurrent also slightly decreased in the range of waveleng ths from 800 to 450 nm and increased from 350 to 540 nm. Heat treatment bef ore irradiation improved the photovoltaic cells. After irradiation by gamma -rays and electron beams, the photocurrent went back to its original value by annealing (for 2 h at 500 degreesC). The capacitance-voltage behavior d ecreased after irradiation and hence the doping decreased. (C) 2001 Publish ed by Elsevier Science Ltd.