Study On The Light Trapping And The Heterojunction Solar Cells

Recently,photovoltaic energy as one renewable energy attracts most of people’s attention with the shortage of energy source and the pressure of climate abnormity.And the research on crystalline silicon solar cells is becoming frontier and hot issue in international research field.The efficiency and cost of solar cells are the key factor for the progress of photovoltaic industry.Heterojunction solar cells have the characteristics of low fabricate temperature and high efficiency.The low-temperature characteristics can reduce the thermal stress and damage of the silicon material,which reduce the requirements of the silicon material and offer the advantage of decreasing the thickness of the cell.Radial junction solar cells absorb photon in the axial direction and transport the carrier in the radial direction,which reduce the diffusion distances of the carrier and is conducive to the carrier collection.So the two structures of the cells meet the development requirements of the high efficiency and low cost.Increasing the light absorption of the solar cells is another way of improving the efficiency.So the light trapping effect of the solar cell is also very critical.The most common light trapping structure is pyramid texture.And the nanowire arrays have a special light trapping effect and are the key factor for fabricating the radial junction cells.To improve the solar cells efficiency,the pyramid structure and the nanowire arrays were fabricated and their light trapping effect was compared.Simultaneously,the radial junction solar cells were fabricated based on the nanowire arrays.Compared with the planar heterojunction solar cell,the radial heterojunction solar cell has better performance.Of course,the defects of the experiment of this paper were pointed out:the size design of the nanowire arrays needs to be improved,and the the cornerite cover of films needs to be further research.In order to guide the experiment,the simulation was carried out by AFORS-HET software before the experiment.In short,the main works are as follows:1)In order to guide the experiment and avoid a lot of repetitive work,numerical simulation of heterojunction solar cells was done and obtain.The AFORS-HET software was used for simulating the(n/i)a-Si/(p)c-Si heterojunction solar cells.The performances of HIT solar cells with different thickness of n-a-Si layer,the intrinsic layer and the density of interface defect states were simulated.The results of the simulation pointed out that the appropriate thickness of the intrinsic amorphous silicon is 5 nm and the most appropriate doping concentration for n-type amorphous silicon is 7×1019 cm-3.And the interface state density should be less than 1012 cm-2eV-1,otherwise there have a great impact on the performance of the solar cell.2)The textured surface which has pyramid shape was fabricated by wet etching.And the influence of the etching time and temperature on the morphology and the reflectivity was researched.When the etching solution consisted of 5%KOH and 2%IPA,heated to 70 ℃ for 35 min,the textured effect was the best.The lowest reflectivity can reach 11%under this condition.And the relationship of the pyramid texture size and the reflectivity was confirmed.The size of the uniform pyramid texture does not affect the reflectivity,but for the non-uniform pyramid texture,the reflectivity of some small pyramid texture with most of the big pyramid texture is the highest.Simultaneously,nanowire arrays were fabricated by lithography and reactive ion etching and the reflectivity of these two textured was contrasted.It is pointed out that nanowire array need to be further optimized based on the experimental results of the paper.3)The radial heterojunction solar cells were fabricated based on the nanowire arrays and obtain the efficiency of 10.88%.It is found that the efficiency of the radial heterojunction was higher than the planar heterojunction by testing the performance of the two type solar cells.But for the radial heterojunction solar cell of this paper,the cornerite cover of the amorphous silicon thin film is a problem,which seriously affects the efficiency of the solar cells.