Preparation And Properties Of Silicon Based Intermediate Band Photovoltaic Materials Based On Heavily Doped Nickel

The intermediate band solar cell(IBSC)is one of the third generation photovoltaic devices,and its theoretical conversion efficiency can exceed the Shockley-Queisser limit.The preparation of intermediate band(IB)materials is the key to the research and application of IBSCs.There are many methods for preparing IB materials,including high mismatch alloys,quantum dot superlattice and supersaturated doping.Among them,supersaturated doping has some advantages from the first two.Its preparation method is relatively simple,which can avoid complex epitaxial process,so it can reduce the production cost,and it is easy to realize large-scale production.In this paper,the transition metal element nickel(Ni)was supersaturatedly implanted into crystalline silicon by ion implantation,and then the samples were annealed by rapid thermal process(RTP).At the same time,experimental equipment such as secondary ion mass spectrometer(SIMS),minority carrier lifetime tester,deep level transient spectrometer(DLTS)and related testing methods were used to measure the ion concentration distribution,minority carrier lifetime change and deep level activation energy of the materials.The formation mechanism of the IB was explored.In addition,the influence of nickel element doping and various preparation factors on the characteristics of the samples was also analyzed.The experimental results are as follows:1.For the experiment of fully activating impurity,SIMS results show that the nickel impurity concentration in the effective doping region of Si: Ni samples exceeds the value of Mott phase transition,indicating that the samples meet the basic conditions of the IB formation.The bulk resistance of the samples also decreases gradually,which proves that nickel metal impurities are effectively mixed into the silicon material,and it reduces the material resistivity and promotes the carrier migration of the materials.The increasing carrier mobility confirms the role of nickel impurity doping and further proves the effectiveness of nickel doping.The minority carrier lifetime of the samples increases gradually,which proves that the non-radiative recombination of the materials is restrained.The increasing ellipsoidal crystallization coefficient shows that nickel impurities are indeed incorporated into the material and destroy the original lattice of the material.The high-temperature annealing is conducive to the repair of the lattice and improve the lattice structure of the material.X-ray diffraction results show that the material has a single diffraction peak,and the peak intensity increases continuously,indicating that the material is a high-purity and stable single crystal phase structure.SEM images show that the surface morphology of the material gradually changes from light gray to clear and profound,indicating that high-temperature annealing improves the morphology and structure of the material.The light absorption coefficient of the sample measured by the spectrophotometer is gradually increasing,and the light absorption capacity of the visible material is enhanced,which proves the effective formation of the IB.2.For the experiment of synergistic regulation of impurity activation and lattice recovery,the bulk resistance of Si:Ni samples decreases gradually,and the lattices of the samples have been recovered more perfectly,indicating that the material properties have been further improved.The Hall mobility increases gradually,indicating that the free carriers are more active.The minority carrier lifetime is increasing,which proves that the non-radiative has been further strengthened.SEM images show that the morphological structure became stronger and more stable.The absorbance of the samples is also increasing,indicating that the light absorption capacity of the material is further enhanced and the structure of the IB tends to be stable.DLTS testing analysis shows that the deep level activation energy of the materials is at about 0.25 e V,indicating that the intermediate band is formed at about 0.25 e V above the valence band of the silicon.It concluded that the crystalline silicon doped with nickel can effectively form the IB materials.At the same time,the optimized annealing process improves the materials structure and enhances the properties of the materials.The relevant results provide an experimental basis and reference for the preparation of high-performance IBSC materials.