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Title:	Investigation of chalcogenide based buffer layers by physical vapour deposition (PVD) technique for high efficiency copper-indium-gallium-diselenide (CIGS) solar cells
Authors:	Puvaneswaran Chelvanathan (P51744)
Supervisor:	Nowshad Amin, Prof. Dr.
Keywords:	Investigation Chalcogenide Physical vapour deposition (PVD) technique Copper-indium-gallium-diselenide (CIGS) solar cells Solar cells
Issue Date:	13-Sep-2011
Description:	Among all thin film solar cells, Copper-Indium-Gallium-Diselenide (CIGS) thin film solar cells with CdS buffer layer have achieved the highest conversion efficiency of 20.3 % to date. However, CdS is usually grown by Chemical Bath Deposition (CBD), which has some major disadvantages, such as CdS is a hazardous material and CBD process yields massive toxic waste which obviously discourages the commercialization of CIGS solar cells using this technology. However, wide bandgap chalcogenide semiconductors such as InS and ZnS are the potential candidates to replace CdS as they have higher cutoff wavelength. Moreover, Physical Vapor Deposition (PVD) technique is more favorable than CBD due to its inherent scalability for large scale in-line production. Hence, the main objective of this study is to fabricate, characterize and evaluate the performance of chalcogenide based buffer layers for high efficiency CIGS solar cells. This study encompasses two parts, which are numerical modeling and practical fabrication. Numerical modeling on the effects of band gap grading of CIGS on the overall performance is carried out by using Solar Cell Capacitance Simulator (SCAPS). Results show that front surface and back surface grading enhance the overall conversion efficiency due to the carrier recombination mitigation at the buffer layer/CIGS and CIGS/back contact heteointerfaces. In addition, prospects of ultra thin CIGS absorber layer is also modeled and it is found 0.5 μm thick absorber layer with incorporation of band gap grading structures yields comparable conversion efficiency with the conventional CIGS solar cells with 2.5 μm thick absorber layer. Lastly, performance evaluation of InS and ZnS based CIGS solar cells are numerically modeled and promising result for InS/CIGS solar cell (efficiency = 17.85%, Voc = 0.693 V, Jsc = 31.80 mA/cm2 and fill factor = 0.8095) and ZnS/CIGS solar cell cell (efficiency = 19.38%, Voc = 0.695 V, Jsc= 33 mA/cm2 and fill factor = 0.8260) are obtained. In practical fabrication of InS and ZnS buffer layers, sputtering parameters such as operating pressure, RF power and substrate temperature are varied and the effects on the structural and optical properties are evaluated. Various characterization methods such as X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscope (SEM), and UVVIS are used to characterize InS and ZnS films. Lower operating pressure (below 10 mTorr), higher RF sputtering power (55 W to 110 W), and higher substrate temperature (100 °C to 200 °C) yields better InS and ZnS films. Moreover, complete CIGS devices are fabricated (Al/ZnO:Al/i-ZnO/buffer layer/CIGS/Mo) with three different buffer layers of CdS, InS and ZnS. The highest conversion efficiency of 6.62 % (Voc = 0.408 V, Jsc = 24.69 mA/cm2 and fill factor = 0.6578) is achieved for CdS/CIGS solar cell, while InS/CIGS solar cell has obtained conversion efficiency of 2.88 % with (Voc = 0.360 V, Jsc = 16.81 mA/cm2 and fill factor = 0.4767) and lastly ZnS/CIGS solar cell has achieved conversion efficiency of less than 1 %. InS and ZnS based solar cells have higher series resistance and low shunt resistance possibly due to the non-optimized ZnO:Al transparent conduction oxide layer as found in this study. Moreover, all layers need optimization for each fabrication step. In conclusion, this study has investigated the potentials of InS and ZnS buffer layers and opened up the usage for CIGS solar cells as a result of theoretical and practical investigation.,Master/Sarjana
Pages:	133
Call Number:	TK2960.P848 2012 3
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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