SummaryAn alternative paradigm for enhancing the light utilisation in photovoltaic (PV) devices is the use of nano-particles of metals in order to make superior use of the optical field. Since the size and shape of nano-particles act as tuning variables for plasmonic effects, it should be possible to design schemes to enhance different PV technologies in wavelength regions where they could perform better. The structures could be introduced at various interfaces within a PV device. Issues are surface recombination and absorption losses, both of which are potentially significant if the density of nanoparticles is high.
In order to thoroughly understand the influence of plasmonics on the PV materials and devices by experiment, carrier lifetime measurements and photoconductivity measurements can be performed. The aim of this project is to produce a test platform which can be used to measure the change in photoconductivity of a thin layer of silicon due to the presence of a variety of plasmonic nanostructures on the surface.
MethodWe have chosen the asymmetric metal-semiconductor-metal photodetector as the basis for our plasmonic structure test platform as these devices are known to have fast response times and high sensitivities. We are optimizing the dimensions of the MSM photodetector, such as distance between metal fingers, width and lengths of metal fingers, thickness of the silicon device layer and thickness of the SiO2 passivation layer using simulations built in Athena/Atlas software. The simulation results are being used to guide the design of MSM devices for our plasmonic structure test platform. Fabrication of the initial MSM devices is currently underway.
Next stepsFollowing fabrication and testing of the MSM devices, plasmonic structures will be placed in between the metal fingers using ebeam lithography and lift-off or deposition from a liquid suspension. Photoconductivity measurements will then be performed using the IV characteristic measurement systems.
Key References1. Barnard, E. S.; Pala, R. A. and Brongersma, M. L. âPhotocurrent mapping of near-field optical antenna resonancesâ, Nature Nanotechnology, 2011, 9, 588-593 2. Chui, C. O.; Okyay, A. and Saraswat, K. âEffective dark current suppression with asymmetric MSM photodetectors in Group IV semiconductorsâ, Photonics Technology Letters, IEEE, 2003, 15, 1585-1587 3. Sesuraj, Rufina S.A.; Temple, T.L. and Bagnall, D.M. âOptical characterisation of a spectrally tunable plasmonic reflector for application in thin film silicon solar cells.â Solar Energy Materials and Solar Cells, 2013, 111, 23-30.