Anthony W. Catalano

Hydrogen plasma interactions with tin oxide surfaces

Abstract We have exposed films of various conductive transparent oxides (CTOs) such as SnO 2 and indium tin oxide to hydrogen plasmas in d.c. and r.f. discharges and have measured the white light optical transmission, the room air work function and the sheet resistances before and after the exposure as a function of the discharge parameters, the sample temperature and the exposure time. In addition, we have determined the surface composition of unexposed and exposed samples by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy and the depth of plasma interactions by AES profiling. Interactions with positive hydrogen ions in the plasma lead to a chemical reduction at the CTO surface. As the main consequence, the optical transmission is decreased by the formation of an absorbing oxygen-depleted surface layer.

a-Si/sub 1-x/C/sub x/:H alloys for multijunction solar cells

a-SiC:H alloys are promising candidates for the top junction alloy in triple-junction solar cells. In order to understand the limitations on electronic transport in the alloys, the photoconductivity and optical absorption were measured using photothermal deflection spectroscopy (PDS). Thin-film transistors have also been fabricated and studied. Taken together, the material and device measurements provide strong evidence that electron transport in the material is restricted by declining mobility in the alloys above a bandgap of approximately 1.9 eV. p-i-n devices based on the alloys have exhibited open-circuit voltages as high as 1.05 V, but the fill factors of the devices decline at these high voltages. The open-circuit voltage of the devices scales with optical bandgap, and measurements of V/sub oc/ versus temperature indicate that generation-recombination controls the open-circuit voltage. Triple-junction devices containing 1.85-eV a-SiC:H and 1.45-eV SiGe:H have shown conversion efficiencies of 10.2%. >

Solar cells: Present status and future prospects

Abstract Some market estimates indicate that a-Si:H based solar cells now account for the majority of sales. Although much of this market is consumer electronics, other conventional power markets may be expected to grow as the performance, reliability and cost of the devices improve. Prospects in each of these areas appear excellent. Although we believe efficiencies of 14% are realistic for single junction devices, multijunction cells will have better efficiencies and stabilities. The high performance in these devices will require improvements in the properties of compatible wide and low bandgap materials. Two of the most promising candidates are a-SiGe and a-SiC:H alloys. In this paper we examine recent developments in these materials and devices.

Correlation between bulk p-layer properties of a-Si1−xCx:H and performance of a-Si1−xCx:H/a-Si:H heterojunction solar cells☆

Bulk p-type material of a-Si1−xCx:H with 0<x<0.5 has been characterized by the optical gap, the reflective index, and the dark resistivity and its activation energy. The optical properties can be well described by existing theories of the dielectric constant of semiconductors. It is shown how the optical and electrical properties of carbon-containing p-layers affect the photovoltaic parameters of a-Si1−xCx:H/a-Si:H heterojunction p-i-n solar cell structures.

Light degradation in I-layers in the glass/TCO/a-Si:H/Pt structure

Abstract Light degradation is studied by quantum efficiency and a.c. I–V measurements, with measuring light entering from either side of the cell. Collection length in the I-layer is reduced by a factor of three after 48 hours of AM-1 light soaking. Blue light response is much better viewed from the glass side, but degrades to the same level as the metal side after light soaking. Hence the glass side cell shows more degradation even thought the final result is the same when viewed from either side. The large change in blue response on the glass side is ascribed to the introduction of the originally suppressed back diffusion at the TCO/a-Si interface.