| Compared with traditional transparent conductive oxide (TCO) thin films such as indium tin oxide (ITO) and SnO2thin films, impurity-doped ZnO thin films are low-cost, non-toxic and resource-rich. As front contact of silicon thin film solar cells, sputtered impurity-doped ZnO thin films show great advantages. Impurity-doped ZnO thin films have great durability against hydrogen plasmas, and could obtain excellent light trapping structures after wet chemical etching. This kind of materials has been paid much more attention due to its advantages in improving conversion efficiency of thin film silicon solar cells. Compared with general Al doped ZnO(AZO) thin films, BZO thin films show more potential as front contacts in thin film solar cells, because of the enhanced transmittance in near infrared light region. The most traditional way of depositing BZO thin films is MOCVD. But BZO thin films deposited by MOCVD have not so much high conductivity. Good electrical properties were obtained in sputtered BZO thin films, but the gap between the melting temperatures of B2O3and ZnO make it much harder to sinter a BZO target, which limited the application in industrial application. In order to avoid these weaknesses, in this thesis, BZO thin films were deposited by sputtering intrinsic ZnO target, using B2H6as doping source. The doping concentration was changed by adjusting B2H6flow rate. BZO films were also applied in thin film solar cells after post treating. The main contents and results are given as follows:(1)The influence of B2H6concentration, B2H6flow rate and Ar flow rate in doping process were investigated. The consequences showed that B2H6concentration didn’t affect substrate doping directly when Ar flow rate was high enough. But changes in B2H6flow rate and Ar flow rate would significantly affect the qualities of BZO thin films. BZO thin films deposited with suitable B2H6flow rate and Ar flow rate show good transmittances in near infrared light regions. A1.Oμm-thick BZO thin film deposited on a0.7mm-thick Eagle XG glass showed a transmittance of68.1%at1200nm wavelength. The resistivity of this film was1.07×10-3Ω·cm.(2)The role of temperature played in depositing process and thermal treatment were investigated. Higher temperature in depositing process and thermal treatment would enhance the crystal qualities of BZO films. After being annealed at a suitable temperature, BZO film got an improved resistivity of5.09×10-4Ω·cm, compared with a value of1.07×10-3Ω·cm before thermal treatment.In this thesis, a novel method of depositing BZO films was used. As the substrate temperature changing regularly during the depositing process, the crystal quality and conductivity of BZO thin films were improved. Films deposited in this way could obtain a resistivity of7.83×10-4Ω·cm without any post treatment.(3) BZO thin films capped with Al layers were annealed at high temperature, which is a novel method of thermal treating was used in this thesis. BZO films annealed in this way could be heated on higher temperature without obvious deterioration in conductivity.In this way, the crystal qualities of BZO thin films could be enhanced. Samples prepared by this method show good conductivities and transmittances. A lowest resistivity of4.64×10-4Ω·cm could be obtained after thermal treating in this way. Moreover, a structure with excellent light trapping could be obtained after Al films being etched. A haze value of96.5%,90.2%,79.6%,61.9%at wavelengths of550nm,800nm,1000nm,1200nm respectively was obtained. Such structure increased short circuit current density (Jsc) of solar cells when films were used as front contacts of microcrystalline silicon solar cells. |
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