Study Of ITO Films Preparation By RF Magnetron Sputtering At Low Temperature And Effect Of Annealing Treatment Of HIT Solar Cell

HIT(Hetero-junction with intrinsic thin-layer) solar cells combining the advantage of crystalline silicon cells and thin-film silicon cells achieve the purpose of low cost and high efficiency. This paper mainly studies the preparation of ITO films at low temperature with RF magnetron sputtering and the effect of annealing treatment of intrinsic hydrogenated amorphous silicon(a-Si:H) layer to HIT solar cells.(1)1)As the upper electrode of solar cell, the photoelectric properties of ITO films and low-temperature preparation have important influence on solar cells. The deposition parameters of O2/Ar flow ratio, sputtering power(P), sputtering pressure(Pg), deposition temperature(Ts) and the target-substrate distance(D) are all optimized one by one and the impact on the change of the deposition parameters of thin films on its XRD, SEM and photoelectric properties. The dependence of the micro structure and conductivity on the changes of parameters is greater than the light transmittance. The larger O2/Ar flow ratio, the better the crystallinity, the resistivity firstly decreases and then increases; sputtering power increases, the preferred orientation of thin films change from(222) to(400), the resistivity continued to decline; the temperature of 100℃, the resistivity reaches the minimum; after annealing, the preferred orientation of thin films is(222) and(400) and the crystallinity and conductivity are all improved, thereby the transmittance basically has no obvious change. The results show that, the optimum process parameters for ITO film deposition are: O2/Ar flow ratio of 0.1/25, sputtering power of 210 W, sputtering pressure of 0.2 Pa, substrate temperature of 100℃and substrate-target distance of 2.0cm and annealed in Ar for 60 min at 200℃. The average transmittance of the prepared ITO films in the visible region is 89.4% and the resistivity is 3.8×10-4Ω·cm. 2)When deposition conditions and thickness of film are all identical, the differences on the micro structure and photoelectric properties of the two kinds of films prepared by DC and RF magnetron sputtering by means of SEM, XRD, conductivity and transmittance,respectively. Then they all be applied to simple hetero junction solar cell and be compared. In this experiment, a comparison of ITO(DC) and ITO(RF)indicates that, the surface morphology of ITO(DC) is more smooth, the grain size is smaller and more uniform distribution than ITO(RF). And the preferred crystal plane of the two is different, the diffraction peak intensity of(222) and(400) has littledifference in ITO(DC), but it is very different in ITO(RF). All of these reasons lead to that the conductivity of ITO(RF) is poorer than ITO(DC), so the application of ITO(RF) is poorer than ITO(DC) on solar cell. The two methods have their advantages and disadvantages, but they all have its suitable scope.(2)The solar cell with and without a-Si:H buffer layer is compared. The insert of a-Si:H buffer layer can make the hetero-junction interface be passived, the carrier recombination decreases, and the solar cell formed with a excellent PN junction. The comparison of solar cell with and without a-Si:H buffer layer prove that open circuit voltage and short circuit current of solar cell with a-Si:H buffer layer are improved.(3)The influence of annealing temperature and time upon HIT solar cell with a-Si:H buffer layer in vacuum is researched. The a-Si:H buffer layer is applied to a simple hetero-junction solar cell after it is heated to 320 ℃ and annealed 60 min.Finally, a HIT solar cell with Voc of 621 m V, short circuit current Isc of 9.965 m A, fill factor FF of 0.45 and the efficiency η of 11.11% is prepared.