Abstract
Photovoltaics are increasingly becoming an indispensable addition to global electrical power generation, and research into more efficient PV devices is key to making this a feasible alternative to more highly polluting power generation methods. To reduce “wasted” light incident on PV cells new surfaces incorporating topographically novel gratings have been created and characterised with the goal of improving light trapping within the glass covering, enhanced levels of transmitted light diffraction and haze, and reduced surface reflection.
By use of a CO2 laser, these glass surface gratings were produced through empirical research, with comprehensive characterisation throughout. Topographical data provided by optical profilometry shows that repeated passes of the laser, coupled with retardation, were able to excavate deeper grating tracks whilst retaining a recognisable track cross section. The development and implementation of a novel asymmetric liquid cooling arrangement provided the required reliability during these exothermic processes.
It was determined that laser pass retardation >100ms gave negligible benefit in reliability other than when glass to air cooling was employed, and no measurable benefit if liquid cooling is utilised. Catastrophic failure of glass samples was evident when cooling was inconsistent, with partial-area insulation causing sufficient thermal stress to enable critical fractures to propagate.
Spectrophotometry focused on the visible light spectrum shows that haze was increased from insignificant levels (74.3% for glass with a 0.3 mm spaced grating in a cross-hatched pattern having undergone 100 passes of a CO2 laser set to 12W output. Light transmission over the same spectral range fell with the application of the grating from 93.3% for unprocessed glass and covered a range of 58.0% to 89.2% across all samples. Performance for the gratings was based on weighted values of both transmission and haze, with greatest performance factor from a 0.3 mm spaced, simple grating of 100 passes at 12W. All of these optimum values were gained from samples which had undergone a washing regime developed over a thorough programme of phased characterisation and ultrasonic bathing in deionised water.
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Speaker's Bio
Stephen Davies is a MRes student at the Faculty of Science and Engineering, University of Chester. His supervisors are Alice Gillett and Simon Hodgeson.