Harvard College

Massachusetts Institute of Technology

Mark T Winkler

Eric Mazur

Michael J Aziz

Tonio Buonassisi

Brian R Tull

Riley E Brandt

Austin Joseph Akey

Method for making thin crystalline or polycrystalline layers. The method includes electrochemically etching a crystalline silicon template to form a porous double layer thereon, the double layer including a highly porous deeper layer and a less porous shallower layer. The shallower layer is irradiated with a short laser pulse selected to recrystallize the shallower layer resulting in a crystalline layer. Silicon is deposited on the recrystallized shallower layer and the silicon is irradiated with a short laser pulse selected to crystalize the silicon leaving a layer of crystallized silicon on the template. Thereafter, the layer of crystallized silicon is separated from the template. The process of the invention can be used to make optoelectronic devices.

Method for producing thin layers of crystalline or polycrystalline materials

Photovoltaic devices (e.g., solar cells) are disclosed that include at least three radiation absorbing layers, each capable of absorbing radiation over a different wavelength range of the solar radiation spectrum. Any two of these three wavelength ranges can be partially overlapping, or alternatively they can be distinct. The layers are disposed relative to one another so as to form two junctions, each of which includes a depletion region. In some cases, the radiation absorbing layers can collectively absorb radiation over a wavelength range that spans at least about 60%, or 70%, or 80%, and preferably 90% of the solar radiation wavelength spectrum. By way of example, in some embodiments, one layer can exhibit significant absorption of solar radiation (e.g., it can absorb at least one radiation wavelength at an absorptance greater than about 90%) at wavelengths less than about 0.7 microns while another layer can exhibit significant absorption of the solar radiation at wavelengths in a range of about 0.7 microns to about 1 micron. The third layer can in turn exhibit a significant absorption of solar radiation at wavelengths greater than about 1 micron.

Multijunction photovoltaic device

Methods and apparatus for processing a substrate (e.g., a semiconductor substrate) is disclosed that includes irradiating at least a portion of the substrate surface with a plurality of short radiation pulses while the surface portion is exposed to a dopant compound. The pulses are selected to have a fluence at the substrate surface that is greater than a melting fluence threshold (a minimum fluence needed for the radiation pulse to cause substrate melting) and less than an ablation fluence threshold (a minimum fluence needed for the radiation pulse to cause substrate ablation). In this manner a quantity of the dopant can be incorporated into the substrate while ensuring that the roughness of the substrate's surface is significantly less than the wavelength of the applied radiation pulses.

Engineering flat surfaces on materials doped via pulsed laser irradiation

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Brooklyn, NY, United States of America

Mark T Winkler