Study On New Type Of Oxide Transparent Conductive Films Applied To Solar Cells

As a direct band-gap compound semiconductor with wide band gap（3.37eV）, ZnO has high transmittance in the visible range, as high as90%or even more. Moreover, ZnO has such advantages as follows: itsabundance in materials, low cost, nontoxicity, easy to achieve excellentdoping, higher thermal and chemical stability under the exposure tohydrogen plasma and nitrogen plasma than ITO. Therefore, ZnO-basedtransparent conductive films especially their doping systems have beenconsidered as an alternative potential material instead of ITO filmsbecause of their comparable photoelectric performance so far. Theresearch of doped ZnO thin films is of important practical significanceand has great pragmatic value. All in all, it has attracted increasinglywidespread attention and become a new research hotspot in the lastdecades. In this thesis, ZnO is chosen as a matrix material. First, ZnO: Al/ZnO bilayer films with high quality transparent and conductive propertieson quartz glass substrates have been prepared by electron beamevaporation technique （EBE）. Curtain means of characterization methodssuch as X-ray diffraction, Hall measurement and transmittance spectra areemployed to characterize the structure, electrical and optical performanceof the bilayer films. We investigated the effect of buffer layer depositiontime equal to buffer thickness and Al doping proportion in the targets onthe properties of the films. The results illustrate that the insertion of ZnObuffer layer can improve the performance of the film. X-ray diffractionmeasurement shows that the crystal quality of the films is improved withthe increase of the film thickness. The optimized experimental conditionsfor gaining films with excellent electrical properties are that the bufferlayer depositing time is30min, which means that the buffer thickness is50nm or so, the Al proportion is1wt%in the targets. It is found that thebuffer layer deposition time and low Al proportion have little effect onthe optical transmittance of the films. However, the optical performanceof the films with high Al proportion becomes lower because of thedecrease of film crystal quality caused by high Al proportion.Next, we make exploratory research on the photoelectric performanceof Eu doped ZnO thin films. ZnO: Eu/ZnO bilayer films on quartz glasssubstrates have been prepared by electron beam evaporation technique. X-ray diffraction measurement also shows that the insertion of ZnObuffer layer indeed improve the crystal quality of the films. We analyzethe effect of Eu doping concentration on the electrical properties of thefilms. The average transmittance in the visible range is above85%. In thecase that the molar ratio of Eu3+and Li+is3:1, the red emission of Eu3+iseffectively induced. As to the luminous mechanism, we explain thephenomenon as follows: Eu³⁺mixed into the ZnO crystal lattices formsmany centers of luminescence. The energy transfers from ZnO to Eu3+.The sensitizer of Li+can be served to assist solvent and compensatecharge.