Investigation of interfacial engineering and charge dynamics in (Sb2S3)-based solar cells
Ee, Ling Gui
Date of Issue2014
School of Electrical and Electronic Engineering
Solid-state dye-sensitized solar cell (ssDSCs) is an emerging technology with the potential to surpass first and second generation solar cells. To date, ssDSC has demonstrated efficiency up to 12.3 %. Challenges due to organic dye stability, degradation and leakage of liquid electrolyte posed difficulties in commercialization. Henceforth, efforts were invested to replace dye and liquid electrolyte materials. A promising semiconductor material antimony sulphide (Sb2S3) owing to its high absorption coefficient (a= 1.8 x 105 cm-1 ) and relatively low band gap (1.7- 1.9 eV) is used to fabricate ssDSCs. For these types of solar cells, the sensitizer is sandwiched in between the mesoporous TiO2 layer and hole-transporting material (HTM). The absorber layer thickness ranges from several nm to tens of nanometers, also known as extremely thin absorber (ETA) solar cells. Antimony sulphide is synthesized by a facile low cost chemical bath deposition (CBD) method. For device fabrication, different strategies were pursued to evaluate antimony sulphide layer in the device. The photo-anode, control of recombination through interfacial layers such as ln(OH)xSy, surface modification and different hole-transporting materials were studied to investigate and enhance photovoltaic performance in devices. Studies on different sized Ti02 nanoparticles allowed a better understanding of the growth mechanism of chemical bath deposition. Although smaller nanoparticle size provides a much larger effective surface area for sensitizer attachment, the smaller pore size leads to an over-aggregation of Sb2S3 particles on the surface pores. An optimum nanoparticle size of> I 00 nm was established and reported to exhibit light scattering effect, achieving an efficiency of2.3% after post treatment. The photo-physical behavior of the annealed prepared by atomic layer deposition (ALD) Sb2S3 was studied by transient absorption spectroscopy (T AS). Crystallized Sb2S3 domains give rise to strong non-degenerate two-photon absorption and slower hot charge carrier cooling ( ~ 17 ps). The crystallized domains also slow down the charge carrier recombination from 7.5 ns to 16.7 ns. The increased light absorption, slower hot charge carrier cooling and charge carrier recombination suggest that the annealed Sb2S3 is more suitable for light harvesting application than the as-deposited. The findings suggest that the significance of tuning the morphology of this material system to enhance its photovoltaic performance.