Abstract
We report on our fabrication and characterization of Al2O3/Si composite nanodome (CND) structures, which is composed of Si nanodome structures with a conformal cladding Al2O3 layer to evaluate its optical and electrical performance when it is applied to thin film solar cells. It has been observed that by application of Al2O3thin film coating using atomic layer deposition (ALD) to the Si nanodome structures, both optical and electrical performances are greatly improved. The reflectivity of less than 3% over the wavelength range of from 200 nm to 2000 nm at an incident angle from 0° to 45° is achieved when the Al2O3 film is 90 nm thick. The ultimate efficiency of around 27% is obtained on the CND textured 2 μm-thick Si solar cells, which is compared to the efficiency of around 25.75% and 15% for the 2 μm-thick Si nanodome surface-decorated and planar samples respectively. Electrical characterization was made by using CND-decorated MOS devices to measure device’s leakage current and capacitance dispersion. It is found the electrical performance is sensitive to the thickness of the Al2O3 film, and the performance is remarkably improved when the dielectric layer thickness is 90 nm thick. The leakage current, which is less than 4x10−9 A/cm2 over voltage range of from -3 V to 3 V, is reduced by several orders of magnitude. C-V measurements also shows as small as 0.3% of variation in the capacitance over the frequency range from 10 kHz to 500 kHz, which is a strong indication of surface states being fully passivated. TEM examination of CND-decorated samples also reveals the occurrence of SiOx layer formed between the interface of Si and the Al2O3 film, which is thin enough that ensures the presence of field-effect passivation, From our theoretical and experimental study, we believe Al2O3 coated CND structures is a truly viable approach to achieving higher device efficiency.
Highlights
Solar cells based on bulk crystalline silicon have been well developed and dominated current photovoltaic markets, much effort has to be made to improve their cost-effeteness in order for2158-3226/2015/5(12)/127209/10127209-2 Zhang et al.AIP Advances 5, 127209 (2015)silicon-based solar cells have much wider adoption
We report on our fabrication and characterization of Al2O3/Si composite nanodome (CND) structures, which is composed of Si nanodome structures with a conformal cladding Al2O3 layer to evaluate its optical and electrical performance when it is applied to thin film solar cells
The ultimate efficiency of around 27% is obtained on the CND textured 2 μm-thick Si solar cells, which is compared to the efficiency of around 25.75% and 15% for the 2 μm-thick Si nanodome surface-decorated and planar samples respectively
Summary
Absorption improvement in c-Si thin film solar cells by means of photonic management (PM) engineering, such as photonic crystals,[4,5] nano-wires (nano-rods),[6,7] nanopores (nanoholes),[8,9] nanocones (nanodomes),[10,11,12,13,14,15] and inverted nano-pyramids[16] has been theoretically studied. All these light-trapping structures inevitably lead to significant increase in the device surface area and introduce surface defects, resulting in elevated carrier loss. Our theoretical analysis and experimental work indicate that application of thin film Al2O3 layer to Si-CND solar cells can lead to strong improvement in the device’s electrical performance, and in the meantime, the optical performance is improved
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