Design And Properties Of Omnidirectional And Efficient Light Management Nanostructures

In recent years,renewable and clean energy resources have attracted people’s attention due to ecological pollution and climate change issues which are becoming increasingly prominent with the rapid development of social economy.Solar energy has become one of the most attractive renewable clean energy sources,due to its huge storage capacity and wide distribution.Solar cells are the most widely used photovoltaic devices,which can convert solar energy into electrical energy that provides an effective way for people to use solar energy efficiently.However,most solar cells have low cost performance due to large amount of materials and poor performance.In order to enhance the performance of solar cells while reducing the amount of materials used,the sub-micron nano light management structure was proposed.This paper proposes nano square optical trap light trapping structure and nanotube light trapping structure.The optical and electrical properties of the two light trapping structures are calculated and studied based on gallium arsenide（GaAs）and polycrystalline silicon（poly-Si）.The main research contents of this paper are as follows:（1）Optical and electrical simulations of nano square optical trap light trapping structure were performed based on GaAs and poly-Si materials,respectively.Through optical simulation,it is found for GaAs materials,excellent light confinement can be achieved within a large range of structural parameters.The structure with height H=800 nm,inner side length W_in=350 nm,and the thickness T=40 nm can produce a photocurrent density of 29.4 mA/cm² under AM 1.5G illumination.The effective thickness is only 407 nm.Under the same illumination,a2000 nm thick flat GaAs film only produces photocurrent density of 19.8 mA/cm².Electrical studies shown the GaAs optical trap structure is more sensitive to surface recombination compared to bulk recombination.The electrical performance of the device will be greatly attenuated if the surface recombination rate is greater than 10²cm/s.Therefore,the surface recombination rate must be controlled below 10² cm/s by means of surface passivation in order to achieve a reasonably high photoelectric conversion efficiency.A 16.87%photoelectric conversion efficiency can be obtained with the minority carrier lifetime is 10^-7 s and the surface recombination rate is 10²cm/s.Compared with normal incidence,the light absorption of the structure appears enhanced under oblique incidence.This confirms that the square optical trap light trapping structure has excellent omnidirectional and efficient light trapping ability.（2）We have studied the optical and electrical properties of the nanotube light trapping structure based on GaAs and poly-Si materials.The influence of nanotube structure parameters on the optical properties of nanotube and the bulk recombination and surface recombination of nanotube impact on electrical performance were studied.For GaAs materials,the structure exhibits good light trapping properties over a wide range of structural parameters.The nanotube struct with height H=1000 nm,the internal diameter D_in=80 nm,the thickness T=75nm and the outer diameter period ratio D_out:P=1:2 can produce a photocurrent of28.2 mA/cm²,when the oblique incidence angle is 60°,a photocurrent density of14.9 mA/cm² can be obtained.The average light absorption of the structure is 88%and 93%,under normal incidence and oblique incident angle of 60°,respectively.The effective thickness corresponding to these parameters is about 1032 nm.This proves the structure has excellent omnidirectional and efficient light trapping ability.The electrical studies indicate that GaAs nanotube devices are sensitive to surface recombination,so surface passivation and other means are needed to improve the electrical performance of the nanotube structure.