Integrated Photovoltaic Device Development
Integrated Device Development
Figure: Spike arrays coated by indium-tin oxide (A); depositing wires into channels (B); 3D electrodes (C); and self-built ALD system (D).
In thin film solar cells, light absorption and charge transport are incompatible. Thicker films absorb more incoming photons, and have higher efficiencies of charge separation. But, the distance for charge carrier transport increases, which leads to a higher probability of recombination. Vertical electrode arrays are proposed to improve performances by absorbing light vertically and transporting charges horizontally. If the spacing between adjacent electrodes is less than the mean free diffusion length of charge carriers (500 nm for organic photovoltaics), the charge can be rapidly transferred before recombination. Dr. Ming Su's group has fabricated vertical glass spike arrays using glass fiber drawing and differential etching, followed by the plasmon enhanced chemical vapor deposition of conductive oxide thin films (Figure A). The glass channels are straight, and the spacing between adjacent channels can be reduced to 300 nm, thus such channels can be used to make narrow-gap electrodes. Highly conducting materials (conducting oxide) will be filled into the glass channels using sol-gel method (Figure B). The height, spacing and diameter of wires, and their arrangement will be changed using different sized channels and etching conditions. The spacing between two adjacent wires can be controlled by thin film deposition. Ordered 3D electrodes will be made (Figure C). The connectivity can be adjusted to allow all wires to be inter-connected to form a single cathode; or the wires that are oriented in one direction are connected as an anode and the wires oriented in another are connected as a cathode. An atomic layer deposition (ALD) was built recently in the PI's lab (Figure D), which can deposit thin films of semiconductors, oxides and metal with precise thicknesses, though at relatively slow deposition rates. After depositing thin films of conducting oxides, semiconducting films will then be deposited as functional materials. Since the spacing of semiconducting wire/tubes is close to the wavelengths of visible lights, and the semiconductors could response to different colored light, the collective interaction of light with ordered arrays of semiconducting wires may lead to improved light absorption and charge generation.
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Dr. Ming Su
NanoScience Technology Center
University of Central Florida
Orlando, FL 32826