AlSb Compound Semiconductor as Absorber Layer in Thin Film Solar Cells

Rabin Dhakal, Yung Huh, David Galipeau and Xingzhong Yan

Department of Electrical Engineering and Computer Science, Department of Physics, South Dakota State University, Brookings SD 57007,

USA

1. Introduction

Since industrial revolution by the end of nineteenth century, the consumption of fossil fuels to drive the economy has grown exponentially causing three primary global problems: depletion of fossil fuels, environmental pollution, and climate change (Andreev and Grilikhes, 1997). The population has quadrupled and our energy demand went up by 16 times in the 20th century exhausting the fossil fuel supply at an alarming rate (Bartlett, 1986; Wesiz, 2004). By the end of 2035, about 739 quadrillion Btu of energy (1 Btu = 0.2930711 W – hr) of energy would be required to sustain current lifestyle of 6.5 billion people worldwide (US energy information administration, 2010). The increasing oil and gas prices, gives us enough region to shift from burning fossil fuels to using clean, safe and environmentally friendly technologies to produce electricity from renewable energy sources such as solar, wind, geothermal, tidal waves etc (Kamat, 2007). Photovoltaic (PV) technologies, which convert solar energy directly into electricity, are playing an ever increasing role in electricity production worldwide. Solar radiation strikes the earth with 1.366 KWm-2 of solar irradiance, which amounts to about 120,000 TW of power (Kamat 2007). Total global energy needs could thus be met, if we cover 0.1% of the earth’s surface with solar cell module with an area 1 m2 producing 1KWh per day (Messenger and Ventre, 2004).

There are several primary competing PV technologies, which includes: (a) crystalline (c-Si), (b) thin film (a-Si, CdTe, CIGS), (c) organic and (d) concentrators in the market. Conventional crystalline silicon solar cells, also called first generation solar cells, with efficiency in the range of 15 – 21 %, holds about 85 % of share of the PV market (Carabe and Gandia, 2004). The cost of the electricity generation estimates to about $4/W which is much higher in comparison to $0.33/W for traditional fossil fuels (Noufi and Zweibel, 2006). The reason behind high cost of these solar cells is the use of high grade silicon and high vacuum technology for the production of solar cells. Second generation, thin film solar cells have the lowest per watt installation cost of about $1/W, but their struggle to increase the market share is hindered mainly due to low module efficiency in the range of 8-11% ((Noufi and Zweibel, 2006; Bagnall and Boreland, 2008). Increasing materials cost, with price of Indium more than $700/kg (Metal-pages, n. d.), and requirements for high vacuum processing have kept the cost/efficiency ratio too high to make these technologies the primary player in PV market (Alsema, 2000). Third generation technologies can broadly be divided in two categories: devices achieving high efficiency using novel approaches like concentrating and

tandem solar cells and moderately efficient organic based photovoltaic solar cells (Sean and Ghassan, 2005; Currie et al., 2008). The technology and science for third generation solar cells are still immature and subject of widespread research area in PV.