1.  Development Of ZnO Film For Solar Cell Application By Thermal Evaporation System And Its Characterizations Aditya Gupta1, Hari Prakash2 & Arun Sarma2 1School of Electrical Engineering, VIT University, Vandalur-Kelambakkam Road, Chennai , Tamil Nadu, India 2School of Advanced Sciences, VIT University, Vandalur-Kelambakkam Road, Chennai , Tamil Nadu, IndiaChennai
ABSTRACT
Bi-layered Zn rich ZnO film has been developed on uniformly etched soda-lime glass substrate using vacuum thermal evaporation system. The experiment has been performed by analyzing samples with different concentrations of etched soda-lime. At the same time, the tray containing the ZnO powder has been covered with mesh grids of different sizes each time. It has been shown this provides relatively lower resistivity and exhibits an excellent light scattering property [1] and relatively good electrical properties of the film. The produced film is characterized with SEM-EDAX, FTIR and DRS setup. This has shown improvement in its performance and quantum efficiency (QE). Thus, the developed glass/bi-layered ZnO film with a Zn-rich layer is a new promising upcoming material since its resistivity is low while its light-scattering property is still high.
Introduction:
Zinc oxide (ZnO) thin films have been extensively applied as front transparent conductive oxide (TCO) films in thin-film silicon solar cells. Since light trapping can increase the optical path length of the light inside a cell structure, and also enhances the amount of light for the electron– hole pair generation in the absorber layer of the cell, it is used to improve the efficiency of solar cells by means of photocurrent.
It was reported that [1] in case of hydrogenated amorphous crystalline (a-Si:H) solar cells, direct deposition of a-Si layer on ZnO layer extracts oxygen from the ZnO lattice, which leads to the formation of oxygen vacancies and a low blue emission region (BER) at the ZnO/p-layer interface. This causes the deterioration of both the ZnO/p-layer interface and the a-Si layer quality.
In response to these problems, and preserve the excellent light scattering property of the ZnO films, the quality of ZnO films was improved by employing a combination of etched soda-lime glass substrates and bi-layered ZnO films.
Bi-layered ZnO films having a Zn-rich (oxygen-poor) layer grown on the top of the main ZnO layer was proposed to lower the amount of unreacted H2O and suppress oxygen extraction from the surface.
This work has confirmed the above research through DRS and FTIR. To enhance the surface morphology of the coated ZnO, mesh grids of different sizes were used to cover the tray containing ZnO powder.
Band Gap Calculation:
Results and Discussion: XRD Results
Kubelka-Munk Function:
Where R is the reflectance
Extrapolation of Tauc Plot on X axis yields the Band Gap [2].
Tauc Plot:
Experimental setup:
The Base Pressure was 10-6 mbar and working Pressure is10-5 mbar.
The density of ZnO was set to 5.6g/cc. The impedance was set to 15.8 Ohms.
The soda lime solution was prepared with 20g Calcium Hydroxide, 9g Sodium Hydroxide and 3g Potassium Hydroxide.
The maximum and minimum concentrated solution was in 250 ml and 450 ml distilled water, respectively.
Big Mesh – Maximum Soda Lime
Big Mesh – Minimum Soda Lime
Small Mesh – Maximum Soda Lime
Small Mesh – Minimum Soda Lime
SEM Images
FTIR Plots
Tauc Plots (through DRS)
Big Mesh
Min Soda Lime
Big Mesh
Big Mesh–Maximum Soda Lime
Big Mesh-Minimum Soda Lime
Small Mesh-Max Soda Lime
Small Mesh–Minimum Soda Lime
Schematic of Thermal Evaporation System
Small Mesh
Small Mesh Max Soda Lime
Small Mesh Min Soda Lime
Big Mesh – Maximum Soda Lime
Big Mesh-Minimum Soda Lime
Conclusion:
Micron layer ZnO film produced on glass substrate in 2 soda lime concentrations.
Initial characterization shows that the band gap of the film is of the order of 3.0 eV.
The XRD plots give 2θ=23ͦ due to presence of Carbon. Hence maximum current should be limited to 5 or 6 Amperes.
References:
[1] Aswin Hongsingthong, Hidetoshi Wada1, Yuki Moriya1, Porponth Sichanugrist, and Makoto Konagai, Jp. Journal of Applied Physics 51, p 10NB03-1 to 10NB035 (2012), References there in
[2] S. Mosadegh Sedghia, Y. Mortazavib, A. KhodadadiaSensors and Actuators B: Chemical, Elsevier (2009), References there in
Poster Presented
29th National Symposium on Plasma Science and Technology & International Conference on Plasma and Nanotechnology Mahatma Gandhi University, Kottayam, Kerala, India 8t – 11 December 2014