Solar Cell Front Electrode Printing Key Technology Based On Laser-induced Forward Transfer

Laser induced forward transfer(LIFT)is a high-precision,non-contact,and mask-free digital printing technology.In the photovoltaic industry,compared to screen printing,LIFT is a new type of printing technology that can effectively avoid silicon wafer breakage and does not have the problem of paste clogging.Therefore,the application of this technology to the preparation of solar cell electrodes is very promising and is also current research hotspots in this field.From the perspective of actual industrial production.This paper takes LIFT-based photovoltaic solar cell front electrode printing as a starting point,and conducts research on the key technologies involved in the process.The specific research content is as follows:(1)The influence of motion parameters on the uniformity of the silver paste film during the operation of the laser-induced front electrodes equipment was modeled and analyzed.The three-dimensional model and uniformity evaluation index of the silver paste film used in the simulation are given,and then the multiphase flow model of silver paste and air is deduced based on the volume of fluid(VOF)method,and the rheological characteristics of the silver paste used in the simulation are described.The finite element simulation of the self-healing properties of the transfer material silver paste with non-Newtonian fluid characteristics was carried out,and then a reasonable observation time was provided for the subsequent simulation of the transportation parameters.The effects of different transmission modes(translation and rotation),different acceleration and deceleration curves,and different silver paste film parameters on the uniformity of film transmission were simulated and the results were analyzed.The results of this part can provide a theoretical basis for the feasibility of printing large-area photovoltaic silicon wafer front grid lines and the selection of suitable movement modes for the equipment during operation.(2)Guided by the above simulation results,a laser-induced front electrodes equipment prototype was built jointly with a partner company,and the effect of transportation parameters on the film uniformity during the above-mentioned laser-induced forward transfer process was further verified by experiments.First of all,starting from the function,the laser transfer equipment built is decomposed into three parts: the laser printing module,the silver paste coating module and the silicon wafer transportation module,and then the overall structure design is carried out.Based on the simulation results in Chapter 2,and other related literature materials,the key equipment such as laser,scanning galvanometer,F-θ lens,laser control card and film transport module is optimized and built.Finally,on the basis of the prototype,the transport experiment of the film under the silver paste with different transportation parameters and different film properties was carried out to verify the validity of the simulation results in Chapter 2.(3)Considering the requirements of printing efficiency when the equipment is actually working,the regulation of laser-induced forward transfer point transfer and line transfer with high galvanometer scanning speed and high laser repetition frequency is studied.First,the laserinduced forward transfer silver paste point array confirms the transfer threshold of the silver paste film under certain parameters,and observes the change rule of the point transfer morphology and the transfer threshold to provide a rough parameter range for the subsequent line transfer.Then compare the high repetition frequency and the low repetition frequency on the same spot pitch,and observe the different situations under the high repetition frequency and the low repetition frequency line transfer.Finally,under high repetition frequency,by controlling the scanning speed of the galvanometer to obtain different spot pitches,the influence of the spot pitch on the morphology of the transferred grid lines can be obtained according to this,and the transfer parameters of the silver paste grid lines with the largest aspect ratio can be obtained at the same time.