In recent years, the need for clean, affordable energy sources has increased. Global concern over pollution created by fossil fuels, rising energy demands, and dwindling oil supplies require new and alternative sources of energy which are clean, cost-effective, environmentally-friendly, and widely available. Photovoltaics (PV), commonly known as solar cells, answer this need by converting electromagnetic radiation into electric energy through a phenomenon known as the photoelectric effect. Solar cells are an attractive solution to the current energy crisis because of the abundant supply of light, environmental friendliness, and scalability. However, current limitations stemming from production and manufacturing methods, limited efficiencies, and a lack of infrastructure limit solar cell use.
In order for solar cell technologies to gain a wider acceptance, the cost of energy ($/Kwh) for the end user must match or be lower than that of energy from utility grids produced by conventional energy sources such as coal. Counter-intuitively, increases in the efficiencies of solar cell modules often increase the cost of energy ($/Kwh) from those modules. Increased manufacturing complexity, increased material cost, and yield dominate the cost per module of high efficiency solar cells and limit their cost-effectiveness. Recent advances in the solar cell industry concentrate on reducing solar cell cost by decreasing material cost, use, and waste. Thin-film solar cell technologies employ these and other innovative production methods to reduce cost ($/Kwh) and increase commercial solar cell use. Further, new manufacturing methods create 3-D light trapping features, without an increase in complexity or waste, which increase solar cell efficiencies.
In the past, producing light trapping features employed photolithography and ineffective etching methods, resulting in increased manufacturing cost, complexity, time, and waste. Additionally, producing 3-D features on thin-film solar cells employing these methods reduces the mechanical strength of the solar cell and increases the likelihood of damage later in the manufacturing process.
Current etching processes used in the semiconductor and photovoltaic industries are inherently limited and are unsuited for producing cost-effective solar cells. Etching processes in use today produce 3-D features on a substrate by first coating that substrate with a material known as a photoresist. The etchant preferentially etches uncoated areas of the substrate. Thus, current etching processes are able to selectively etch surface layers of a semiconductor through the use of a photoresist.
However, this process is undesirable for many applications and a need exists for etching practices that can selectively etch middle layers of a semiconductor without damaging the outer layers, decrease etch time, and increase the selectivity of an etchant without using a photoresist. An enhanced selective etching process produces a sufficiently strong 3-D thin-film silicon substrate cost-effectively without damaging the reusable template used in the 3-D TFSS process.
U.S. patent application Ser. No. 11/868,489, entitled “METHODS FOR MANUFACTURING THREE-DIMENSIONAL THIN-FILM SOLAR CELLS” by Mehrdad Moslehi and incorporated by reference herein, presents a new manufacturing process for producing 3-D thin-film silicon solar cells in which prior art manufacturing methods may not be suitable.