Fabrication And Characterization Of Tio2/In(Oh)Xsy/Sns Composite Eta Solar Cell

ABSTRACT

A highly structured TiO2/In(OH)xSy/SnS solar cell has been developed based on the Extremely Thin Absorber (ETA) concept. In this set up, TiO2 formed the window layer, In(OH)xSy was used as a buffer layer while SnS was used as the thin absorber film. Its small band gap (~1.3eV) makes it more appropriate for optical absorption. Titanium Dioxide (TiO2) thin films was prepared by spray pyrolysis. Deposition time for TiO2 films varied in the range of 1-4 minutes that gave film thickness of 51.02- 69.48 nm. Thereafter, thermal annealing in argon at 400 0C was done. Thin films of In(OH)xSy were deposited by chemical precipitation onto glass substrates. Thereafter, they were optically and electrically characterized as deposited and after annealing in the range 100 0C-300 0C. Chemical Bath Deposition method was also employed in depositing SnS films onto FTO glass substrates for electrical optimization of the films that were deposited at 700C. Deposition times for the SnS were varied in the range of 40-75 minutes prior to characterization. The In(OH)xSy and SnS thin films on glass substrates have electrically been characterized using a Keithley 2400 Source Meter while TiO2 films on fluorine doped Tin Oxide have been characterized by employing a SRM-232 surface resistivity meter. The optimized electrical resistivity and sheet resistance of In(OH)xSy, TiO2 and SnS thin film has been found to be 9.03±0.30 Х 107 Ωcm, 13.54 Ω/□ and 2.46 Х 105 Ωcm respectively. TiO2, In(OH)xSy and SnS thin films optimized for ETA solar cell had a band gap of 3.16 eV, 3.73 eV and 1.25 eV respectively with optical properties appropriate for window, buffer and absorber layer. Testing of the fabricated ETA solar cell has been done by a solar simulator that provides an illumination almost equivalent to the natural sunlight. Keithley meter and the solar simulator interfaced, current-voltage curve was extracted. The cell exhibited a short circuit current, Isc of 0.00245 A, open voltage, Voc of 0.0473 V, efficiency, η of about 0.53 % and a fill factor, FF of 0.551. This low efficiency was due to low shunt resistance and high series resistance of the fabricated cell. The values of optimized respective thin films before cell fabrication compare well with values that have obtained by other researchers as depicted in literature. It was concluded that annealed In(OH)xSy, SnS and TiO2 films were appropriate as a buffer, absorber and window layer respectively for solar cell applications especially within the VIS- IR light spectra owing to their optical and electrical properties that were realized in this research.