Next Generation Multilayer Graded Bandgap Solar Cells

Abstract

Direct conversion of light energy into electrical energy or photovoltaic technology has continually developed over the past five decades. Solar panels based on silicon and thin-film solar panels based on CdTe and CuInGaSe2 are now in the market. The cost of solar panels have reached~ 1.0$ Wà1, and further reduction to~ 0.5$ Wà1 will enable this technology to become a main stream energy supply in the future. Scientific research in this field should therefore be directed towards next-generation solar cells. Key features of these solar cells should be low cost of manufacturing, high conversion efficiency and durability over a period of three decades. Availability of materials required and their non-toxic nature are also important factors. High conversion efficiencies can only be achieved by harvesting photons from all energy ranges, across the ultraviolet, visible and infrared radiation regions. Devices with many bandgaps have been proposed in the early 1960s, but experimental attempts were scarce. There are few reports in the literature on grading of one layer of a p-n junction and achieving improved device parameters. However, work has not progressed forward in order to develop high performing devices. One of the authors of this book (IMD) published graded bandgap devices based on II–VI materials in 2002 and improved this idea to fully graded devices between the front and back electrical contacts in 2005. These devices were experimentally tested during the same year to achieve outstanding device parameters confirming the validity of the new designs. These fully graded devices also benefit from “impurity PV effect” and “impact ionisation” to enhance photo-generated charge carriers. With the experimental confirmation, authors focussed their work on graded bandgap devices based on low-cost, scalable and manufacturable electroplated materials. This book covers several important areas in the field. The book summarises the results of electroplating of semiconductors and details on three main solar energy materials: ZnS as a buffer layer, CdS as the window layer and CdTe as the main light-absorbing material. Growth details and material characterisation using most appropriate techniques are presented. This will serve as a handbook for new and established researchers to continue work in their research fields.