Study Of Anti-reflection Texture And PCD Tools Cutting On Photovoltaic Crystal Silicon

Micro-textured surface can effectively reduce the optical loss of monocrystalline silicon solar cells and improve the photoelectric conversion efficiency of solar cells.Alkali corrosion technology is widely used for traditional monocrystalline silicon solar cells to prepare random pyramid texture.However,due to the restriction of silicon crystal structure,the anti-reflection performance of random pyramid texture is difficult to achieve great improvement.So it is of great value to explore a new antireflection texture and its processing technology for reducing the reflectance and improving the photoelectric conversion efficiency of solar cells.In this paper,a V-ring groove texture for anti-reflection was designed,and a calculation model was established to calculate the weighted reflectance of this textue.Furthermore,the effects of structural parameters on the reflectance of V-ring groove texture are studied.Then,the calculation model of the stress field induced by scratching single crystal silicon is established.The aub-surface stress distribution in scratching of silicon is discussed and the critical undeformed chip thickness for ductile-brittle transition in cutting of silicon is studied.At last,the experimental study on cutting V-ring groove texture of silicon with a polycrystalline diamond(PCD)cutting tool is carried out,and the machining quality of the texture and wear mechanism of PCD cutting tool are discussed.The main work of this paper is as follows:(1)Considering the tip shape of V-shaped PCD cutting tools,a V-ring groove texture is designed for the antireflection of monocrystalline silicon solar cell.Based on the optical principle,the reflectace calculation model of V-ring groove texture is established by ray tracing algorithm.The effects of structural parameters on the reflectance of V-ring groove texture are studied,and the structural parameters of V-ring groove texture are determined by considering the actual machining conditions.It is found that V-ring groove texture has more excellent antireflection performance.Under normal incident sunlight,the weighted reflectance of V-ring groove texture is 5.53%,and the weighted reflectance is reduced by 47.5%compared with the 10.54%weighted reflectance of random upright pyramid texture.(2)Based on the anisotropic physical properties of single crystal silicon,a calculation model of stress field induced by scratching is established.The subsurface stress distribution induced by scratching scratching silicon(100)surface along[001]direction and[011]direction are analyzed,and the relationship between the subsurface stress distribution and the nucleation position and propagation direction of the median crack was studied.It is found that the nucleation position and propagation direction of median cracks are affected by indenter shape and scratching direction.The relationship between the nucleation or propagation angle of median cracks and the half angle of conical indenter is approximately in accordance with the Boltzmann function in the process of scratching silicon(100)surface along[001]direction.While the relationship between the nucleation or propagation angle of median cracks and the half angle of conical indenter is approximately in accordance with the linear function in the process of scratching silicon(100)surface along[011]direction.(3)Based on the crack propagation mechanism in nano-scale of Si-Si bond,the calculation model of anisotropic fracture strength of single crystal silicon was established,and the cutting force model in cutting of silicon was established by considering the anisotropy of monocrystalline silicon.The stress distribution on the elastoplastic interface of silicon subsurface was calculated.A nucleation and propagation criterion for median cracks in silicon subsurface was established,and the critical undeformed chip thickness for ductile-brittle transition in cutting of silicon was defined as the maximum undeformed chip thickness that would not induce the nucleation and expansion of median cracks.The effects of crystal orientation,friction coefficient in cutting process,negative rake angle of cutting tool and nose radius of tool tip on the critical undeformed chip thickness were studied.It was found that the critical undeformed chip thickness in cuuting of silicon showed anisotropy with the change of cutting direction.A large critical undeformed chip thickness can be obtained by reasonable selection of tool parameters.When the friction coefficient in cutting process is in the range of 0.05 to 0.30,using a cutting tool with rake angle of-40 degrees is more conducive to ductile cutting of single crystal silicon.And a sharp tip is also beneficial for increasing the critical undeformed chip thickness.(4)The V-shaped polycrystalline diamond(PCD)cutting tool was used to perform cutting experiments of V-ring groove texture on silicon surface.The quality of the machined texture was analyzed.It was found that there were pit damages at the bottom of V-ring grooves,and side walls of machined V-ring grooves collapse due to small width of unmachined parts between the structures.In addition,the cutting tool suffered from edge wear in the process of continuous large-area texturing,and the main form of tool breakage is micro chipping.