Study On Photoelectric Properties Of Mg₂Si Heterojunction For Thin Film Solar Cells

The fabrication and photoelectric properties of Magnesium Silicide?Mg₂Si?/Si heterojunction were studied.The influences of the thickness of Si and Mg films on the structure,morphology,optical and electrical properties of Mg₂Si/Si heterojunction were analyzed.Firstly,Mg₂Si films were grown on silicon and glass substrates by magnetron sputtering and high vacuum annealing.Two kinds of heterostructures of Mg₂Si/p-Si and Mg₂Si/n-Si are designed based on Mg₂Si thin films.This paper mainly studies the preparation of Mg₂Si/p-Si and Mg₂Si/n-Si thin film heterojunction on p-Si?High resistance:R>3000?,Low resistance:R<1-5??and n-Si?High resistance:R>2000?,Low resistance:R<1-10??,and the effect of deposition of different thickness of Mg film on the surface morphology of Mg₂Si/p-Si and Mg₂Si/n-Si thin film heterojunction.By using the optimal preparation process,the samples were annealed at 400?for 5 hours.It was found that Mg₂Si films were formed under these conditions,thus forming Mg₂Si/p-Si and Mg₂Si/n-Si film heterojunction.The results show that the XRD peaks of Mg₂Si films prepared on Si substrates of different specifications are in good agreement with those of Mg₂Si standard,which indicates that the single phase Mg₂Si films are prepared.At the same time,the Mg₂Si films grown on Si substrates have preferential growth characteristics at?220?.Through the analysis of the prepared Mg₂Si surface morphology by using scanning electron microscopy?SEM?,it can be seen that,in general,with the increase of the deposited Mg film thickness,the surface morphology of the heterojunction of Mg₂Si/Si film becomes denser and the grain continuity increases.At the same time,the effects of depositing Si films with different thickness on glass substrates on the preparation of Mg₂Si films were studied.The results show that as the thickness of the deposited Si film increases,it helps to form a continuous thin film layer.The prepared samples were annealed at 400?for 4 hours,and then the samples were tested by XRD and SEM.It was found that all Mg₂Si films were formed.Secondly,the absorption and transmittance of Mg₂Si/p-Si and Mg₂Si/n-Si thin film heterojunction were measured by UV-VIS-NIR spectrophotometer.The effects of the thickness of the deposited mg films on the absorption and transmittance of the Mg₂Si/p-Si and Mg₂Si/n-Si thin film heterojunctions were studied.The results show that the surface morphology of Mg₂Si films on p-type Si substrate is discontinuous and uneven when the deposited mg films are thin,which is one of the reasons for the decrease of light absorption.At the same time,Mg₂Si/p-Si thin film heterojunction was fabricated on p-type low resistance Si substrate.The absorption spectrum of the structure in the wavelength range of 500-900 nm was significantly.Meanwhile,using the hall effect test system respectively on the p-type silicon?High resistance:R>3000?,Low resistance:R<1-5??and n-type silicon?High resistance:R>2000?,Low resistance:R<1-10??on the preparation of Mg₂Si/p-Si and Mg₂Si/n-Si thin film heterojunction mobility of hall,hall coefficient,sheet carrier concentration,carrier concentration test.Through the electrical properties of the Mg₂Si/p-Si thin film heterojunction prepared on a high-resistance Si substrate,it was found that the whole structure had a low carrier mobility,especially when the Mg film was deposited at500 nm,the hall mobility of the Mg₂Si/p-Si thin film heterojunction formed was only0.74cm²/Vs.The electrical properties of Mg₂Si/p-Si thin film heterojunction prepared on a low resistivity Si substrate showed that the deposited Mg film thickness increased from 340 nm to 540 nm,and then decreased and then increased.Through the preparation of Mg₂Si/n-Si thin film heterojunction on the high-resistance Si substrate,it is found that with the increase of the deposited Mg film thickness,Mg atoms are gradually abundant,the scattering probability of the matrix in the Mg₂Si/n-Si structure decreases,resulting in the gradual increase of hall mobility.Through the electrical properties of the preparation of Mg₂Si/n-Si thin film heterojunction on the low-resistance Si substrate,it is found that the hall mobility of the preparation of Mg₂Si/n-Si thin film heterojunction on the low-resistance Si substrate is the highest,mainly because the hall mobility is mainly determined by the effective mass of carriers and the scattering probability.Finally,using the Newport-oriel 94041A solar cell I-V test system respectively on the p-type silicon?High resistance:R>3000?,Low resistance:R<1-5??and n-type silicon?High resistance:R>2000?,Low resistance:R<1-10??on the preparation of Mg₂Si/p-Si and Mg₂Si/n-Si thin film heterojunction volt-ampere characteristics at room temperature,980m W/cm²under simulated light conditions.The results showed that the increasing of forward bias,the resistance of the corresponding film heterojunction increases.This indicates that the metal electrode indium?In?did not form a good ohmic contact with the semiconductor heterojunction,but formed a schottky contact,which was caused by the negative deviation of the schottky junction when the positive bias voltage increased.