Performance Study Of MOCVD-ZnO:B Films And Its Application In Thin Film Solar Cells

Zinc oxide (ZnO) is an n-type wide band-gap compound semiconductor with the wurtzite structure,which has a wide direct band gap of3.37eV at room temperature. And it has excellent piezoelectric, optical, pressure sensitive and other features, what’s more, its abundant raw materials without toxicity, high optical transparency and electrical conductivity. Compared to ITO, a doped ZnO (ZnO:B) has comparable electrical, optical, rich in raw materials and low cost. And owing to high stability in hydrogen plasma, ZnO films as transparent conductive oxide (TCO) in solar cells have been extensively investigated. In order to practical application of ZnO films, and improve the efficiency and stability of Si thin-film cells, and accelerate industrialization, ZnO films which has back reflectors and textured light-trapping front electrodes were fabricated using metal-organic chemical vapor deposition (MOCVD) technique on glass substrates, and then,which were used in solar cells.Firstly, the undoped ZnO films were fabricated by using metal-organic chemical vapor deposition (MOCVD) technique on glass, and the influence of substrate temperature, chamber pressure, gas flow rate and film thickness on films crytalline, morphologies, electrical and optical properties have been systematically studied. It was found that substrate temperature has dramatical influence on the surface morphology of the ZnO films, the opportune substrate temperature facilitated the growth of textured ZnO film. A proper chamber pressure could make sure the ZnO have good films’crystalline quality. The gas flow rate affect the electrical stability of ZnO films. The ZnO front and back electrodes require different film thickness, and the thickness also work on surface morphology of ZnO film. We found that the high-quality conductive undoped ZnO films was fabricated in the condition of180℃,1.0Torr, DEZn/H2O100/55(sccm,DEZn/H2O),which has texture surface morphology,low resistivity,high electron mobility and high transmittance.Secondly, Base on the former study of undoped ZnO films, the structural, optical electrical properties of ZnO film doped at different B2H6flow rates was investigated in detail. Boron-doping decreased the resistivity of ZnO film dramatically, and improved the stability of ZnO film. But boron-doping also changed the influence of substrate temperature. The best substrate temperature was lower, moreover, a significant Burstein-Moss moving phenomena was observed, it means a significant increase in the optical band gap. The high-quality back reflectors and textured light-trapping front electrodes were fabricated at the substrate temperature of160℃and170℃Finally, ZnO:B film were introduced into a-Si thin film solar cells as front electrodes and back electrodes. The cells were fabricated on glass by plasma enhanced chemical vapor deposition (PECVD) method. MOCVD-ZnO films presented equal performance with SnO2film. The cells’with ZnO:B open circuit voltage (Vos), short-circuit current (Isc), conversion efficiency and fill factor were390mv,3.73mA,8.01%and0.446.