Photovoltaic Device Applications of Porous Silicon

Abstract

We report on the results of our investigation of using porous Si to enhance the performance of crystalline silicon photovoltaic solar cells. Possible approaches include using the porous Si for (1) surface texturing to enhance light trapping, (2) front or back surface fields because of its wider bandgap, and (3) photon color conversion of blue light to longer wavelengths that have higher quantum efficiency in a Si solar cell. In our surface texturing study, a porous-Si-covered single-crystal Si wafer showed an integrated reflectance of only 1.4% at 500-nm wavelength compared to about 40% for a polished Si surface. For our solar cell study, we used a point-contact cell structure with diffused p+ and n+ point contacts on the back of the cell. This cell structure allows us to form the porous Si on the front surface after both the junction formation and the evaporation and alloying of metal contacts.

Characterization of Si nanostructures using internal quantum efficiency measurements

“…This scheme is based on electrochemical etching of Si to convert top surface layer into a porous material. Tsuo, et al, [16] have reported on reflection properties of porous Si. However, there are many problems associated with porous Si in solar cell structures.…”

“…Nevertheless, large area, RIE-textured mc-Si solar cells with an efficiency of -17.1 % have been reported [15]. Another similar approach aimed at reduced reflection requires anodic etching of Si to forma porous layer at the front surface [16]. Porous Si also supports a wide range of nanoscale features with broadband reflection reduction similar to black Si surfaces.…”

High-performance porous silicon solar cell development. Final report, October 1, 1993--September 30, 1995

“…Recently, a group at NREL described their efforts with applying porous silicon technology to the preparation of photovoltaic devices. 9 Their approaches included using the porous silicon for surface texturing to enhance light trapping, using the wider bandgap of porous silicon to provide a surface fi eld to reduce recombination losses, and seeking to have photoluminescence in porous silicon down-convert incoming ultraviolet light to visible for better response. Indeed they found that the presence of porous silicon greatly decreased the refl ectivity of silicon wafers, bringing it as low as 1.5% at 500 nm.…”

Improvement in Photovoltage and Stability of Porous n-Si Electrodes Coated with Platinum by Regulation of the Thickness of Nanoporous Layers

“…Considerable studies have been made on solar cells using porous Si. For p−n junction based solid-state solar cells, − porous Si is used mainly for a decrease in the surface light reflectance and an increase in the photocurrent density. For photoelectrochemical (PEC) solar cells, − the situation is rather complicated, a variety of photocurrents, photovoltages, and stabilities being reported probably because of differences in the detailed structure of porous (or nanoporous) Si layers.…”