Solar Cell Transparent Electrode And Proton Irradiation Of Triple Junction Solar Cells Research

With the progress of solar cell science and technology,the characterizations and improvement of solar cell materials,along with the development and innovation of characterization methods for new structural solar cells,are all meaningful and valuable studies.From the two points of view,the work in this thesis mainly consists of the study of contact properties of IMO(a novel TCO material) sputtered on Si,and the attempt of novel methods of induced defects detection and degradation characterization for proton-irradiated high-efficiency GaInP/GaAs/Ge triple-junction solar cells.The main content includes the following four parts:1.Study of IMO/Si.A novel transparent conductive film In₂O₃:Mo(IMO) was sputtered onto Si wafer,and IMO/Si heterojunctions formed.For IMO/p-Si contact,current-voltage(I-V) measurement showed typical rectifying characteristic.A relative large built-in potential was obtained by investigating the capacitance-voltage(C-V) characteristic,from which the schematic band alignment of IMO/p-Si was plotted.Then the band alignment of IMO/n-Si could be.deduced,and the I-V curves could be well explained.There is a narrow electronic potential well close to the interface,and the C-V curve was affected by it.Reverse saturate current-temperature(I₀-T) measurement gave an active energy E_ac,which represents the transition from the top energy level in the narrow well to IMO.The measurement of photocurrent spectrum showed signals of three discrete levels in the narrow potential well,and the energy of the transition from the top level to IMO agrees well with the E_ac.Further,based on the Poisson's equation,theoretical calculation of conduction band shape of IMO/Si was processed,and the obtained discrete levels in the narrow potential well could be compared well with the results from photocurrent spectra.Also the C-V curve was calculated,and it agreed well with the experimental data.2.ODLTS measurement system was set up.Based on the original DLTS system, pulsed exciting light was set through laser diodes controlled by pulse-generator, and the pulse parameters are convenient to set freely now.3.Optical deep level transient spectroscopy(ODLTS) technique has been used to measure defects in GaInP/GaAs/Ge multi-junction solar cells for the first time. Three modes of ODLTS were managed to detect defects in the top two sub-cells of this triple-junction cell separately,and their levels and concentrations were calculated.For one non-irradiated sample,only one intrinsic level in top sub-cell at low temperature was observed,while several levels were observed for the irradiated samples.Two defects levels in GaAs middle cell could be found in single-junction GaAs ce,lls reported by former literature.By computational simulation,the distributions of radiation-induced defects in the samples were given.4.Impedance spectroscopy(IS) measurements have been carried out to study the degradation of proton-irradiated GaInP/GaAs/Ge triple-junction solar cells.By IS measurement and analysis,parallel resistance and capacitance of each p-n junction for all the three sub-cells of the triple-junction solar cell were deduced in terms of a simple ac RC equivalent circuit.Optical method was used to distinguish the three measured RC units from each other.For the non-irradiated sample,the three measured capacitance of each p-n junction agrees well with the calculated result,while for the irradiated samples,the variation of R and C of each sub-cell related with proton energy agrees well with the results of SRIM simulation.