Characterization of Cu2S / SnO2: F P-N Junction for Solar Cell Applications
Omwoyo, Jared Gisemba
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Due to industrialization and increase in population, there is need for clean, green and renewable source of electrical energy. Traditional sources of electrical energy like fossil fuels are getting depleted, on the other hand silicon based solar cells are expensive hence the need for low cost and reliable alternative source of energy. Photovoltaic is a reliable energy source which is renewable. Photovoltaic is a process of conversion of solar energy to electricity directly using solar cells. For this study Copper (I) Sulphide (Cu2S) thin films were deposited on glass substrates by Chemical Bath Deposition (CBD) technique. Copper sulphate (CuSO4) was used as a source of copper ions, thiourea (CS (NH2)2) as a source of sulphide ions and tartaric acid as a complexing agent, ammonia solution was used to regulate the pH. SnO2: F thin films were deposited using spray pyrolysis technique (SPT) on glass substrates at substrate temperature of 3500 C using pentahydrated stannous chloride (SnCl4∙5H2O) and ammonium fluoride (NH4F) as precursors. Optical transmittance and reflectance of all film samples prepared in the range of 200 nm-1100 nm were measured using UV-VIS-NIR spectrophotometer. The optical measurements were simulated using SCOUT software to obtain optical constants. Cu2S deposited at 0.15 M Cu2+ exhibited low average transmittance of 20.91 %, high average absorbance of 51.29 % and narrow optical band gap of 2.33 eV hence a good absorber material to be used as p-type layer in solar cells applications. On the other hand, SnO2: F had high average transmittance of 79.94 % and wide optical band gap of 4.04 eV at 4 % concentration of fluorine. This shows that SnO2: F is a suitable n-type layer for solar cell applications. Cu2S had lowest refractive index of 1.44 at 0.15 M Cu2+. The four point probe was used to measure the sheet resistivity of all thin films. SnO2: F had lowest resistivity of 40.3 Ω cm at 4% concentration of fluorine while Cu2S had low resistivity of 0.40x103 Ω cm at 0.15 M Cu2+. .The Cu2S/SnO2: F p-n junction was fabricated in phases. First the n-type layer of SnO2: F was deposited onto the glass substrate by spray pyrolysis method and then the p-type layer of Cu2S thin films was deposited onto SnO2: F thin film to form a p-n junction. The solar simulator was used to measure the I-V characteristics of the fabricated cell. The fabricated cell had open circuit voltage (Voc) of 0.4075 V, short circuit current (Isc) of 0.00219 A, fill factor (FF) of 0.61 and efficiency (η) of 0.303 %. Therefore, Cu2S and SnO2: F thin films are suitable materials for fabrication of Cu2S/SnO2: F p-n junction solar cell.