| ZnO:Al (AZO) thin film has low resistivity and high transmittance in the visible light range, and is stable against the bombardment of the H ions and active H atoms. These excellent properties make it the best potential substitute for the Sn-doped In2O3(ITO) as a transparent electrode for solar cells.β-FeSi2 has a small band gap and large optical absorption coefficient higher than 10-5cm-1, which makes it a good choice for the bottom sub-cell of the tandem solar cell. These two materials are nontoxic and their constituents are abundant which meet the requirements of the third generation solar cells. Deposited on quartz and silicon substrates at high temperature, AZO films show excellent optoelectrical properties which are close to those of ITO. Andβ-FeSi2 films with good crystalline quality have been prepared on Si substrate.This thesis mainly studies the deposition of AZO films with good optoelectrical properties on low cost soda lime glass and flexible substrates. And the preparation of good-crystallizedβ-FeSi2 on quartz were also studied. On the basis of the study mentioned above, the structure of the quartz/AZO/β-FeSi2 was prepared tentatively.In this thesis, AZO films with excellent optoelectrical properties were deposited on soda lime glass and organic flexible substrates, respectively, by radio frequency (RF) magnetron sputtering using ZnO:Al2O3(98:2 wt%) ceramic target. The effects of the process parameters of the RF sputtering on the structural, electrical and optical properties of the films have been studied. According to the results, the optimal parameters for the solar cells were determined as: 300°C, 0.15Pa, 150W, 20sccm for the substrate temperature, the work pressure, the sputtering power and the Ar flow rate, respectively. Under this condition, 920nm thick AZO films which has the resistivity of 4.35×10-4Ω·cm, carrier concentration of 4.61×1020cm-3, carrier mobility of 31.37cm2·V-1·s-1 and the average optical transmittance of 80.07% in the range of 400900nm were obtained on the glass substrate.After etching for 15 second by the 0.5 wt % HCl acid, the surface morphology of the AZO films prepared with different Ar flow rate were studied. It is found that with the Ar flow rate of 20sccm, the AZO film has the best textured surface morphology structure (TSMS).To block the diffusion of the impurity from the glass, an Al2O3 buffer layer was inserted between the glass and the AZO. Compared with the AZO without the buffer layer, the transmittance of the AZO film with 3nm Al2O3 buffer layer has no obvious decrease while its resistivity decrease 29.3%. This resistivity is almost the same as that of the AZO films deposited on quartz substrate at the same condition.The AZO thin films were deposited on the organic flexible substrates and glass substrate at the room temperature. It is found that the target race track depth (t) can influence the properties of the AZO films largely, which is ascribed to the distribution of the sputtering gun. Under the conditions of t>4.0mm and t<0.5mm, the properties of the AZO films on polyethylene naphthalate (PEN) were studied comparatively. At t>4.0mm, the AZO films have higher growth rate, higher crystalline quality, smoother surface, lower resisitivity, higer transmittance and optical band gap than the films prepared at t<0.5mm. At t>4.0mm, the crystalline quality and optoelectrical properties of the AZO on glass are better than those of the films on the organic flexible substrates. The crystalline and electrical properties of the AZO on PEN are better than those of the AZO on polyethylene terephthalate (PET).Using RF magnetron sputtering and ion beam sputtering, Fe/Si multi-layered films were prepared and single phaseβ-FeSi2 was obtained after annealing. The influences of the Fe/Si sub-layer thickness ratio (RFe/Si) on the crystallization, surface morphology and optical properties were studied. The sample with high RFe/Si has smoother surface and larger grain size, but the sample with small RFe/Si has better crystalline quality. Single phaseβ-FeSi2 with good optical property was successfully obtained on the quartz substrate, and the band gap of the film is 0.87eV.The effects of the boron (B) doping on the band structure ofβ-FeSi2 were studied by the first-principle calculation. The results show that the B atoms preferentially substitute the position of the Si atoms in the crystal structure of theβ-FeSi2 and make theβ-FeSi2 p type doped. According to the experimental results, the surface of the B-dopedβ-FeSi2 films is rougher than that of the undoped sample. The optical band gap of the B-doped samples is slightly lower than that of the undoped one. The B-dopedβ-FeSi2 films are p-type. With increasing of the B doped amount, the carrier concentration of the films increases, while the resisitivity and mobility decrease. The highest mobility is 39.04cm2·V-1·s-1 when the carrier concentration of the same sample is 2.35×1017cm-3. The highest carrier concentration is 1.16×1019cm-3 when the mobility is 2.08cm2·V-1·s-1.Quartz/AZO/β-FeSi2 structure was prepared for the first time. Theβ-FeSi2 film on the AZO film has a better crystalline quality than that deposited on the quartz substrate directly. Meanwhile,β-FeSi2 film protects the AZO film from being destroyed under the high temperature annealing.
|
PDF Full Text Request