FABRICATION OF ZNO/CU2O AND TIO2/CU2O HETEROJUNCTION SOLAR CELL USING SPRAY PYROLYSIS METHOD.

Abdussalam Balarabe Suleiman, Sabiu Said Abdullahi, Chifu E. Ndikilar and Sabo Isiyaku. Physics Department, Federal Universıty DutseP.M.B 7156, Dutse, Jigawa State, Nigeria. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


…………………………………………………………………………………………………….... Introduction:-
Semiconductors oxides have attracted attention due to their potentials to serve as an alternative to silicon based solar cells, (Zulkiflee et al., 2016), (Fujimoto et al., 2013), (Jayathileke et al.,2007). Cu 2 O is mostly p-type semiconductor oxides, having a cubic crystal structure with a space group of Pn3m, its direct band gap of 2.1eV make it possible to possess high optical absorption property in visible spectrum thereby become suitable material for high efficient solar cells. Moreover, Cu 2 O is nontoxic, inexpensive, readily available and have low production costs which satisfy the environmental and economical requirements needed for large-scale applications in solar cell devices, gas and humidity sensors etc (Zulkiflee et al., 2016), (Jayathileke et al.,2007), (Pavan et al., 2015)., (Saehana and Muslimin, 2013). Nowadays interest is focused on metal oxides heterojunction solar cell because of their advantage of a low price compared with silicon base solar cell (Pavan et al., 2015). Among the metal oxides materials, ZnO emerge to be a good candidate because of its peculiar properties over others, as they serve as a window layer to the Cu 2 O layer. ZnO is a good electron acceptor n-types semiconducting material with a wide band gap ranged from 3.1eV to 3.37eV (Sharma, et al., 2012). This property enables it to have a reasonable number of applications in science and technological world such as optoelectronic devices (Light emitting diode, laser diode, photoelectrons, transistors etc) and solar cell (Fujimoto et al., 2013), . Moreover, its free exiton binding energy of 60eV and transparency in 0.4-2μm optical wavelength range gives it more possibility to be utilized as liquid crystal display devices, electro luminescence and also as transparent conducting oxide materials (Chen, et al.,2009)., ( Karunakaran, et al.,2011). In a similar manner, TiO 2 is a famous n-types materials with the wide band gap of more than 3eV having diverse functionalities as well as being a high efficient crystallites material with high dielectric constant.

ISSN: 2320-5407
Int. J. Adv. Res. 5 (12), 1834-1841 1835 These materials can be utilized as microelectronic devices, photocatalyst, and also used as a heterojunction solar cell devices. (Zulkiflee et al., 2016), (Fujimoto et al., 2013), (Palmieri, et al., 2008), (Gu et al., 2013). With these remarkable properties and in line with its high index of refraction of 2.7 give it more chance of usage as multi layer interference filter, antireflection coating, optical wave guide as well as window layer to the high absorber layer material for solar cell applications (Oku et al., 2014)., (Siripala et al., 2003), (Chergui et al., 2011). Many heterojunction solar cells made of Cu 2 O have been reported using differentmethods. However, the efficiency of the cell is not that much. 0.15% efficient p-Cu 2 O/n-TiO 2 thin film heterojunction solar cell has been fabricated using electrodeposition by (Hussain et al., 2012). ( solar cells using spray pyrolysis method. This is due to its low cost process, easy means of deposition that can be up scale for the large area and vacuum medium is not needed during the deposition process.
Experimental:-Cleaning step:-Before the deposition, the substrate was emerged in to a sonicator containing 1g of Sodium loren sulphate mixed with distilled water for 6minutes followed by refluxing it with methanol using the sochcelet extractor to avoid any contamination. The bottle for the solvents was rinsed with the ethanol to remove any impurities.
Preparation of ZnO and TiO 2 films:-N-type ZnO film is prepared first using 0.1M Zinc acetate (BDH) mixed with 50ml of pure ethanol, the mixture was stirred using a magnetic stirrer until the solute dissolved completely, 400 microliter of the solution was sprayed on top of FTO glass using electro dynamic spray pyrolysis machine at the rate of 2400 microlit/hr and a temp of 350⁰C. Similarly, TiO 2 film was prepared using 0.05M Titanium chloride (BDH) with 50ml of pure ethanol. The mixture was stirred using a magnetic stirrer and centrifuge for 20 minutes until all the titanium chloride dissolved completely, 400 microliter of the solution was sprayed on top of FTO glass substrate using electro dynamic spray pyrolysis machine at the rate of 2400 microlit/hr and a temperature of 450⁰C. For both ZnO and TiO 2 , the distance between the spray nozzle to the substrate was 8mm and the atomization voltage of 3500V was used.

Preparation of FTO-ZnO/Cu 2 O-Cu and FTO-TiO 2 /Cu 2 O-Cu solar cells:-
P-type Cu 2 O was electrodeposited on top of both ZnO and TiO 2 thin layers with 0.05M cupric sulfate and 3.0M lactic acid solution at a bath temperature of 60°C and electrodeposition potential of −0.6 mV for 20min. The pH was adjusted to 9 with the help of 0.1M NaOH. A graphite rod is served as a counter electrode and Ag/AgCl acted as a reference electrode. After deposition the samples were rinsed with distilled water, dried in air and a cupper contact was stuck on the Cu 2 O thin layer.

Results and discussion:-EDX measurement:-
Prior to the completion of the cell deposition, the elemental analysis of ZnO and TiO 2 films was performed using Energy Dispersive X-ray (EDX) spectroscopy. Figure 1 show the EDX spectra of the films. The results comply with what is expected from the films deposition where by the composition of all the films deposited tallies with the outcomes of the EDX spectra. The spectrum contains all the expected elements and no impurity was found.
1836    (1) where α is linear absorption coefficient,υ is light frequency, and A is the proportionality constant. The power of the parenthesis, n is taken equal to 1/2 for direct band gap materials, the absorption coefficient α is determined using ………………………………………… (2) where d is the thickness of the film, R and T are the reflectance and the transmittance respectively (Abdullahi et al., 2015) . for Cu 2 O, TiO 2 and ZnO respectively, which are within the range of the theoretical results (Pavan et al., 2015)., (Siripala et al., 2003).