| CZTS has a band gap that matches the solar spectrum and a high light absorption coefficient,and its constituent elements are very abundant and low-cost.The lattice mismatch between CZTS and Si substrate is slight.However,the maximum photovoltaic efficiency of p-CZTS/p-Si heterojunction solar cells is only 5.8%,which is much lower than that of traditional CZTS solar cells on Mo-coated soda-lime glass substrate.In this thesis,the CZTS thin film solar cells on Si substrate were calculated numerically by heterojunction solar cell simulation software Afors-het.The problems of the structure of p-CZTS/n-Si cells were revealed,and a new structure of n-ZnO:Al/i-ZnO/n-Cd S/p-CZTS/p-Si was proposed and simulated.On this basis,CZTS films were prepared on p-Si substrate by magnetron sputtering and sulfurization.The effects of annealing temperature,annealing time and Na-doping on the microstructure,composition and morphology of CZTS films and the interfacial phase structure,morphology,composition and electrical contact characteristics between CZTS films and p-Si substrates during annealing heat treatment were studied.The results are summarized as follows:(1)The maximum conversion efficiency of p-CZTS/n-Si cells simulated by Afors-het is18.57%.The p-CZTS is the window layer and n-Si is the absorber.However,most of light cannot pass through the p-CZTS and then be absorbed by n-Si,which limits the conversion efficiency of the cell because of the high light absorption coefficient of p-CZTS.A novel structure of n-ZnO:Al/i-ZnO/n-Cd S/p-CZTS/p-Si solar cells with p-Si as the substrate is proposed.The dark J-V curves of p-CZTS/p-Si structures are linear,indicating the formation of ohmic contact between p-CZTS and p-Si.The maximum photovoltaic efficiency of solar cell of new structure reaches 28.41%without considering the parasitic series and parallel resistance and defect state.(2)CZTS films without secondary phase can be prepared on p-Si substrates.With the increase of annealing temperature from 480?to 560?,the full width at half maximum of XRD peak decreases and the grain size of the films increase and the compactness of the films become better.The Cu/(Zn+Sn)of all the samples are close to 0.8.The absorption coefficients in the visible light range are all greater than 1×104cm-1,and the band gap is close to 1.5 e V.CZTS/p-Si is in ohmic contact.The resistance of CZTS/p-Si structure decreases with the increase of annealing temperature.(3)When the annealing time was 0.5h,1h and 1.5h,CZTS films prepared on p-Si substrates have(112)crystal face preferred growth and have no secondary phase.When the annealing time was 1.5h,the film is smooth and compact,and the maximum particle size can reach 750nm.The I-V characteristic curves of CZTS/p-Si structure are liner indicating the formation of ohmic contact between p-CZTS and p-Si.The slope of I-V curve increases with the increase of annealing time,and the total resistance of CZTS/p-Si structure decreases.(4)Na-doping CZTS fabricated by sputtering Na F layer before the deposition of precursor of CZTS.Na-doping can improve the adhesion between p-Si substrate and CZTS thin films.The maximum particle size of CZTS is 800nm when the Na F sputtering time is390s.With the extension of Na F sputtering time,the CZTS peaks in XRD and Raman spectra are enhanced,and the slope of I-V characteristic curve of CZTS/p-Si structure increases significantly,which effectively improve the interface contact between CZTS and p-Si.In summary,the calculated results show that the n-ZnO:Al/i-ZnO/n-Cd S/p-CZTS/p-Si solar cell can solve the problems existing in the p-CZTS/n-Si structure and it is an appropriate structure for CZTS solar cell on Si substrate.Properly increasing the annealing temperature,annealing time and Na-doping amount can improve the characteristics of CZTS films on p-Si substrates,thereby reducing the resistance of the CZTS/p-Si structure and improving the interface contact characteristics between CZTS and p-Si substrates. |
PDF Full Text Request