Methods for manufacturing three-dimensional thin-film solar cells

Abstract

Methods for manufacturing three-dimensional thin-film solar cells 100, using a template. The template comprises a template substrate comprising a plurality of posts and a plurality of trenches between said plurality of posts. The three-dimensional thin-film solar cell substrate is formed by forming a sacrificial layer on the template, subsequently depositing a semiconductor layer, selectively etching the sacrificial layer, and releasing the semiconductor layer from the template. The resulting three-dimensional thin-film solar cell substrate may comprise a plurality of single-aperture unit cells or dual-aperture unit cells. Select portions of the three-dimensional thin-film solar cell substrate are then doped with a first dopant, while other select portions are doped with a second dopant. Next, emitter 525 and base metallization regions 532 are formed.

Description

[0001]This application claims the benefit of provisional patent applications 60 / 828,678 filed on Oct. 9, 2006 and 60 / 886,303 filed on Jan. 24, 2007, which are hereby incorporated by reference.FIELD[0002]This disclosure relates in general to the field of photovoltaics and solar cells, and more particularly to methods for manufacturing three-dimensional (3-D) Thin-Film Solar Cells (TFSCs). Even more particularly, the presently disclosed subject matter relates to methods for manufacturing 3-D single-aperture and dual-aperture TFSCs.DESCRIPTION OF THE RELATED ART[0003]Renewable, high-efficiency, and cost-effective sources of energy are becoming a growing need on a global scale. Increasingly expensive, unreliable, and environmentally-risky fossil fuels and a rising global demand for energy, including electricity, have created the need for alternate, secure, clean, widely available, cost-effective, environmentally-friendly, and renewable forms of energy. Solar photovoltaic (PV) electricit...

AI Technical Summary

Problems solved by technology

However, due to relatively low solar cell efficiencies (e.g., less than 12% for most thin-film technologies and roughly 12% to 18% for most crystalline silicon solar cell technologies), high costs of raw materials (e.g., silicon for crystalline silicon wafer solar cells) and manufacturing processes, limitations on cost-effective and efficient electrical storage, and a general lack of infrastructure to support solar cell proliferation, to date there has been limited use of this energy solution (currently, electricity generation by solar photovoltaics accounts for less than 0.1% of total worldwide electricity generation).

Crystalline silicon wafers offer higher performance, but at higher costs (due to the relatively high cost of starting monocrystalline and multicrystalline silicon wafers).

Thin-film technologies may offer lower manufacturing costs, but typically at lower performance levels (i.e., lower efficiencies).

For both approaches, the price-per-watt typically increases as cell efficiencies rise (due to higher material and/or manufacturing costs).

Due to a rapid annual growth rate of more than 40% during the past ten years and the concurrent demands for silicon material by both semiconductor microelectronics and solar PV industries, the solar PV industry has been experiencing a shortage of polysilicon feedstock supply.

The polysilicon feedstock shortage has significantly constrained the solar PV industry growth, particularly during the past several years.

In fact, the solar cell industry currently consumes over half of the worldwide production of high-purity polysilicon feedstock.

This has led to large increases in the price of monocrystalline and multicrystalline silicon wafers, which now account for roughly half of the total solar module manufacturing cost.

This wafer thickness reduction, however, presents additional challenges related to mechanical rigidity, manufacturing yield, and solar cell efficiency.

While very-high-volume solar fabs in the range of 100 MWp to 1 GWp should facilitate longer term cost reductions (including LCOE) through high-volume manufacturing economies of scale, the relatively high initial fab investment costs, which may easily exceed $100M, may impose certain limits on solar photovoltaic fab construction options.

TFSCs typically offer low cost, reduced module weight, reduced materials consumption, and a capability for using flexible substrates, but are usually much lower in efficiency (e.g., usually 5% to 12%).

In the case of prior art thin crystalline silicon films, there are a number of major problems and challenges with the use of flat silicon films (such as epitaxially growth silicon films with thicknesses below 50 microns) for low-cost, high-performance solar cells.

These include: relatively low solar module efficiencies (typically 7% to 12%), field degradation of module efficiencies, scarce and expensive absorber materials (e.g., In and Se for CIGS and Te for CdTe), limited validation of system field reliability, and adverse environmental impact of non-silicon technologies such as CIS/CIGS and CdTe.

With regard to the prior art crystalline silicon (c-Si) thin-film solar cell (TFSC) technology, there are difficulties associated with sufficient surface texturing of the thin silicon film to reduce surface reflectance losses, while reducing the crystalline silicon film thickness.

This places a limit on the minimum flat (co-planar) monocrystalline silicon thickness due to production yield and cell performance (efficiency) considerations.

In the case of a flat or co-planar film, it is essential to use surface texturing since the reflectance of an untextured crystalline silicon film is quite excessive (can be greater than 30%) and result...

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