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Embargoed until 2018-08-30
Copyright: Pakhuruddin, Mohd
Embargoed until 2018-08-30
Copyright: Pakhuruddin, Mohd
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Abstract
Incomplete light absorption makes effective light-trapping (LT) crucial for realising higher short-circuit current densities (Jsc) in liquid-phase crystallised silicon (LPC Si) thin-film solar cells on glass superstrate. Through a systematic investigation, this research aims to develop, optimise and incorporate different LT features (improving both light-coupling and light-trapping) into 10 um thin solar cells crystallised by a continuous wave diode laser on borosilicate glass. The features include anti-reflection (AR) layers, back surface reflectors (BSRs), Si texturing and glass texturing. Potential Jsc estimated from optical characterisation is used to optimise different LT features. The optimised features are then incorporated into active solar cells and the actual Jsc is derived from external quantum efficiency measurement.
An AR foil is used on the front air-side of the glass to improve broadband light-coupling. With the foil, the Jsc is increased by 1.1 mA/cm2 (5.5% enhancement). BSRs are evaluated to enhance long wavelengths absorption. The optimum BSR is found by combining silver nanoparticles, white paint and the AR foil, with Jsc of 23.3 mA/cm2 (18.9% enhancement).
Si texturing is done by wet chemical etching to increase long wavelengths absorption. Porous mask texturing, ammonium fluoride and potassium hydroxide-based solutions (KOH) are evaluated. KOH-based texturing is the best method, with Jsc up to 25.4 mA/cm2 (24.5% enhancement), when combined with white paint BSR and AR foil.
Glass is mechanically abraded to enhance broadband absorption. Following abrasion, prolonged glass etching resulting in surface roughness below 600 nm is required to enable a successful crystallisation of the Si films on the textured glass. The films exhibit large grains of several hundred micrometers in width and up to centimeters in length, similar to the films crystallised on planar glass. A significant broadband absorption enhancement is achieved, but electrical degradation is observed in the solar cells, indicating incompatibility of the e-beam evaporated LPC Si solar cells with the textured superstrate.
The most effective LT scheme for the LPC Si solar cells on glass superstrate is realised by the rear Si texturing (with KOH-based solution) combined with white paint BSR and front AR foil, with Jsc of 25.4 mA/cm2 (24.5% enhancement).