Electricity produced by coal, nuclear power, and natural gas accounts for almost 90% of the total electricity produced. Although this would suggest higher electricity prices as well as higher energy prices in general, photovoltaic is one technology where the prices are actually going down. The total number of photovoltaic modules shipped for installation has increased by more than a factor of ten in the period of 1982-2005, and has doubled in the period of 2002-2010. Crystalline silicon (c-Si) solar cells and modules have dominated photovoltaic (PV) technology from the beginning. They constitute more than 85% of the PV market today. One of the reasons for the domination of crystalline silicon in photovoltaics is the fact that microelectronics has greatly developed silicon technology. Among various solar cells multicrystalline-Si (mc-Si) solar cell maintains a tradeoff between cost and efficiency. Multicrystalline silicon technology represents roughly 80% of the c-Si market on a rupees per watt basis and dominates over other technologies such as thin film silicon, CdTe and CIGS. Mc-Si wafers have a variety of defects which affect the carrier transport and increase the recombination at the junction. Defects are dominant sites for impurity precipitation, and typically remain ungettered and unpassivated during solar cell processing. Because they are highly concentrated in mc-Si wafer they significantly degrade opto-electrical behavior of solar cells. Due to shunting, they negatively impact open-circuit voltage (Voc), short circuit current (Jsc) and fill factor. Sequential mc-Si wafers were obtained from different part of ingot. Alternate wafers were processed into solar cells. The unprocessed wafers were used to obtain the mapping of defects by PVSCAN. The processed solar cells were characterized by dark and illuminated current-voltage (I-V) plots, Lock in Thermography (LIT), Light beam induced current (LBIC), Electroluminescence (EL) and photoresponse mapping. Mc-Si wafers were also characterized through the fabrication of mesa diode arrays. These diode arrays were used to measure a variety of substrate and cell parameters including resistivity, diffusion length, Voc, Jsc, fill factor and current-voltage characteristics for analysis of the electronic transport properties. Mesa diode arrays were also used to generate a correlation between cell parameters and defect density experimentally. We also created a model for silicon solar cell to see the reliability of experimental results on mesa diodes. The comparison between experimental and modeling results showed good agreement between two results. Mc-Si wafer with an average defect density of 0.64 X 105 /cm2 produces a cell efficiency of 15.5%.
Dr. Vinay Budhraja has received B. Tech degree in Electronics and Communication Engineering from Institute of Engineering and Technology, Kanpur in 2004 and M. Tech degree from Indian Institute of Technology Kanpur in 2007 and PhD degree in Electrical Engineering from New Jersey Institute of Technology (NJIT) in 2012. During PhD, from July, 2008 - December, 2011 he worked full time at National Renewable Energy Laboratory (NREL) through the joined collaboration of NJIT with NREL. From January, 2012 – August, 2013 he worked as a postdoctoral research fellow at Department of Electrical Engineering of University of Arkansas at Fayetteville, USA. From January, 2014 – July, 2014 he worked as a post doctoral research fellow at Sandia National Lab, USA. His research interests include semiconductor devices like solar cells, MOS, thin film transistors etc. and renewable energy based on solar. In 2009, he received best poster award at 34th IEEE PVSC.