Study Of The Micro-columns’ Effects On Improving The Performance Of Solar Cells

With the rapid growth of the economy, energy development and inhibition of pollution have become the core elements of social development. Solar energy is considered as one of the most potential renewable energy. As a main application form of solar energy, solar cells have attracted a lot of attention. Among all kinds of solar cells, crystalline silicon solar cells (both mono-and multi-crystalline) have always been the dominant ones in practical commercial applications. Improving the performance of crystalline silicon solar cells has always been the research focus of companies and labs. Solar cells with radial junctions are considered to have great potential in making low-cost and high-efficiency solar cells with their special surface structures and carriers collection properties.Here proposed in this article is the work on the comparisons of the antireflection properties and the performance of columnar and planar solar cells. How the quality of the materials and the radius of the columns influence the performance of solar cells with radial junctions have also been studied. Several important results have been obtained from our study.1) The chemical etching method which has been widely applied in the industry and the Inductively Coupled Plasma (ICP) etching method have been combined together. These techniques help fabricate textures on the tops and sides of the wires, which can introduce multi-reflectance into the structure and reduce the reflectivity. Both the experimental and simulatice results prove that the microwire solar cells have better performance in antireflection and absorprtion.2) The microwire structures exhibit complex reflection property. When the wavelength of the incident light is around 500nm, the columnar structure with radius of 6μm can reduce the reflectivity more than 40%, comparing to the columnar structure with radius of 12μm. However, when the wavelength of the incident light is around 800nm, the reflectivity of the columns with radius of 12μm is 14% lower than that of the columns with radius of 6μm. By analyzing the collection properties of the carriers generated by incident light of different wavelength, columns with shorter radius have better antireflection effects since they exhibit better absorption properties in the’more importantly’short wavelength part.3) Radial junctions can improve the Isc and efficiency of the solar cells effectively, and the increase of the ratio has exceeded 16% and 10%, respectively. The reflectivity, EQE, IV curves and efficiency results of columnar and planar solar cells have been compared. And the columnar solar cells have better performance in all these parameters mentioned above than the planar ones, especially in Isc and efficiency.4) How the radius of microwires affect the cell’s performance has been studied. The External Quantum Efficiency (EQE) and Isc of the microwire solar cells with radius of 9μm are higher than those of the microwire solar cells with radius of 9μm by over 10%(around 900nm) and 3.5%, respectively. The influence of the minority carrier lifetime of materials on the performance of the solar cells has also been studied. The columnar solar cells made by materials with lifetime of 1.0μs improve the EQE and Isc by more than 10%(around 900nm) and 6.4% respectively, comparing to the columnar solar cells made by materials with lifetime of 0.5μs. Influenced by the quality of the pn junction and the contact resistance of the grating electrodes, microwire solar cells with shorter radius do not exhibit higher efficiency. However, according to the results of ISc*Vov, microwire solar cells with shorter radius have greater potential in fabricating high-efficiency solar cells.5) The efficiency of the microwire solar cells has been improved by 20%. In the study, multi-crystalline silicon with minority carrier lifetime of 0.5μs and 1.0μs has been used. By combing the lab and industry techniques together, multi-crystalline silicon microwire solar cells with efficiency over 14% have been prepared (14% is much higher than the reported highest efficiency of mono-and multi-crystalline silicon microwire solar cells, which are 12% and 7% respectively). After improving the preparation process and technique (such as improving the design of grating electrodes), the efficiency of the microwire solar cells would be more competitive. This suggests that the industry technique can be applied in producing high-quality microwire solar cells, which may lay a foundation for the large-scale fabrication of microwire solar cells. Moreover, this also proves the great potential of the solar cells with radial junctions in making high-efficiency and low-cost solar cells.