Research On Regenerative Cycle Technology Of Crystalline Silicon Solar Cell

Crystal silicon solar cells have become the main energy source of photovoltaic cells due to their long service life and renewable advantages.At present,there are silicon solar cells,multi-component thin film solar cells,polymer multilayer modified electrode solar cells and nanocrystalline solar cells,among which crystalline silicon solar cells have a market share of 80%to 90%.The precious metal resources in crystalline silicon solar cells are mainly concentrated on the frame and the positive and negative materials of the crystalline silicon cell.The theoretical service life of crystalline silicon solar cells are about 25 years,but in the process of using,due to the degradation of the performance of the cells itselves or the aging of the packaging materials,the performance of the solar cells are degraded and cannot be used normally.If the solar cells are directly landfilled or incinerated,it will not only pollute the environment,but also cause waste of resources.Due to the abundant solar energy resources,Qinghai Province has become the main frontier of China's photovoltaic development with the resource conditions,technical advantages and application basis of large-scale development of photovoltaic power generation projects.Therefore,it is urgent to study the reasonable method of recycling waste solar cells to realize the reuse of high-purity silicon and precious metals in waste solar cells.At present,scholars have studied the separation of cell sheets and glass cover plates by organic solvents or heat treatment.However,there are few studies on the regenerative cycle of precious metals in solar cells.This thesis focused on the high-purity silicon and precious metals in the large-scale use of crystalline silicon solar cells for green recycling.The process was simple and easy,and the precious metal in the cell was regenerated directly.The metal resources were recovered by the alkali leaching-precipitation method and the acid leaching-recrystallization method,and the HF acid was used to remove the anti-reflection layer to obtain a relatively pure silicon wafer.The surface morphology of the cell before and after metal removal was characterized with the scanning electron microscopy?SEM?,the crystal form of the recovered product was characterized with X-ray diffractometry?XRD?,the element content on the surface of the cell was analysed with X-ray energy spectrum?EDS?,the impurity on the surface of the silicon wafer was analysed with X-ray photoelectron energy spectrometer?XPS?,and the purity of the recovered silicon wafer was analysed with X-ray fluorescence spectrometer?XRF?.The main research contents and results are as follows:?1?The thermal weight loss experiment was carried out on the encapsulation film EVA on the surface of the cell sheet,and the effects of different heating rates on the final weight loss temperature were discussed.The results show that during the weight loss process,the heating rate only affected the peak value of weight loss in the DSC curve.It had no effect on the final weight loss rate of EVA.At different heating rates,the end temperature of EVA weight loss was 600?,and the weight loss rate reached98.88%.Therefore,the waste crystalline silicon solar cell was calcined in the muffle furnace at 600?for 1 h could well remove the encapsulant film coated on the surface of the cell sheet-EVA.The calcined cell sheet was tested by ICP,and the content of main metal was elemented finally.Among them,Al accounted for 6.97%and Ag accounted for 0.12%in the cell sheet.?2?Using NaOH as the leaching medium of aluminum in the waste crystalline silicon solar cell sheet,the infiuence on leaching concentration and leaching efficiency of aluminum of different NaOH concentration,reaction temperature,solid-liquid ratio of cell sheet and NaOH solution were discussed.The optimum leaching conditions for NaOH is as follows:NaOH solution concentration with 20%,leaching temperature with 20?,solid-liquid ratio with 60 g/mL,and the leaching efficiency of aluminum was 96%under the optimum conditions.Using the leachate as a raw material,the aluminum in the leachate was recovered by chemical precipitation method.Since the precipitate was a colloid,there was a loss in the filtration and drying process,and the recovery efficiency of aluminum was 89%.The recovered aluminum hydroxide was detected by ICP,and the aluminum content was 87.04%in the obtained product,and a relatively pure aluminum hydroxide was obtained.?3?Using HNO₃ as the leaching agent to extract the silver in the battery,the infiuence on leaching concentration and leaching efficiency of silver of different HNO₃ concentration and the solid-liquid ratio of cell sheet and HNO₃ solution in the waste crystalline silicon solar cell were investigated.The optimum leaching conditions for HNO₃ is as follows:HNO₃ concentration with 5 mol/L,solid-liquid ratio with 60 g/mL,and leaching efficiency of silver was 95%under the optimum conditions.Using the leaching solution as a raw material,the silver in the leaching solution was recovered by the recrystallization methodand and the recovery efficiency was 70%.The recovered silver nitrate crystal was detected by ICP,and the silver content was 62.98%in the obtained silver nitrate crystal,a relatively pure silver nitrate was obtained.?4?Using HF to remove the anti-reflection layer on the front side of the crystalline silicon solar cell,the infiuence on the time of removing the anti-reflective layer of the waste crystalline silicon solar cell of different leaching concentration and the solid-liquid ratio were discussed.The optimum leaching condition for HF is as follows:HF concentration with 20%and the solid-liquid ratio was 60 g/mL.After 11minutes,the anti-reflection layer could be removed.The atomic content and existence of the main impurity carbon?C?,oxygen?O?,boron?B?and phosphorus?P?in the silicon wafer was tested by EDS and XPS.It was found that the XPS detection results were basically consistent with the EDS test results.The atomic ratio of C and O is around 1.6.The recovered silicon wafer was analyzed by X-ray fluorescence spectroscopy?XRF?,and the purity of the silicon reached 99.91%,obtained a relatively pure silicon wafer.