Minority Carrier Lifetime Of Silicon Materials Measurement System Based On Microwave Frequency-shift Method

Solar energy is the most promising renewable green energy, solar power technology becomesthe research hotspot. The minority carriers’ lifetime of the silicon which solar cells are made of,determines the solar cells’ conversion efficiency, the longer the minority carriers lifetime thehigher the conversion efficiency. The study on measurement methods of minority carriers’lifetime provides scientific basis during the process of designing and producing solar cells.The theory of minority carriers’ lifetime in Silicon is introduced, and the significant meaning ofcarriers’ lifetime to solar cells is pointed out. Several traditional methods on measuring minoritycarrier lifetime in Silicon are discussed. Based on analysis of traditional methods’ principle,system architecture and their advantages and disadvantages, improvements to the techniquemeasuring photoconductivity decay by means of microwaves are proposed, the superheterodyne detection technique of the reflected microwave signal is described, and a newmethod measuring the minority carriers’ lifetime based on microwave frequency-shift isdesigned.The structure of the system and functions of each module are described in the paper.Theoretical analyses of each functional module are given and their designs have beenaccomplished. The content of design work in this paper includes: determination of themicrowave frequency, the design of microwave oscillator; determination of light source thatmotivates the non-equilibrium carriers in silicon material; analysis of method about microwavefrequency-shift, design and test of frequency shifter; design of detection and analysis circuit ofmicrowave reflection signals.The measurement method of minority carriers’ lifetime discussed in the paper has the charactersof non-contact and non-destructive, it’s the effective way to test and monitor the materialproperties of the solar cell.