| Cu based I-III-VI chalcopyrite-structure compounds have attracted great interests for potential optoelectronic devices applications, which can be applied in both thin film solar cell and photodetector. To lower the cost and increase the band gap of CIS for different application, it is necessary to dope with congeners for CIS. Nowadays the element of Ga is used for CIS doping. However, the elements of In and Ga are scarce and expensive, which limit the large-scale production of CIGS thin film. Therefore more and more attentions have been paid to lower the cost for high-performance optoelectronic devices. In this work, we select Al element as the replacement of In element for CuInSe2 (CIS) thin film. Compared to the disadvantage of In element, the Al element is abundant and cheap. In addition, due to the radius of Al element smaller than that of In element, the band gap of Al doped CuIn1-xAlxSe2 (CIAS) thin film can be adjusted over a much wider rang:from 1 eV for CuInSe2 to 2.7 eV for CuAlSe2. The radio-frequency (RF) magnetron sputtering process and selenization process were employed for the preparation of CIAS thin films. The CIAS-based photodetector have been prepared and the electrical and optical propertied also have been studied. In addition, the CIAS solar cell was prepared. The main innovative results is summarized as follows:1. Preparation of CIS thin films and the effect of composition on structure, optical and morphology properties of CIS thin films. The CIS thin films were prepared by RF magnetron sputtering process and then selenization of precursors. The EDX results show that with the selenization temperature of 550℃, the composition of CIS thin films selenized by Cu-rich metal precursors shows significantly deviation, which were in Cu-poor state. The surface of Cu-poor CIS thin films exhibits cauliflower-like, and the cauliflower-like particle is likely to be the mixture of CIS phase and In2Se3 phase. The Raman spectra show that the intensity of A1 mode is decreasing due to the films with significantly composition deviation. Although composition deviation is serious, the CIS thin films also belong to the chalcopyrite structure, which indicates that the CIS-based solar cell have a high tolerance on composition.2. The CIAS thin films are successfully prepared by RF magnetron sputtering process and the selenization process. The selenization temperature has deep influence on structural property of films. In addition, with the increasing replacement of In element by A1 element the lattice volumes show a reduction, and the band gap of CIAS thin films increases. With the selenization temperature of 520℃, the XRD result indicates that the A1 element can’t dope into CIS lattice and replace of In element. Only if the selenization temperature increases to 550℃, the A1 element has enough energy to dope into CIS lattice. With the increasing A1 content of selenization temperature at 550℃, the XRD (112) diffraction peak and Raman A1 mode frequency exhibit blueshift, which indicate the lattice shrink. In addition, the optical band gap of CIAS thin films shows an increase from 1.28 eV to 1.47 eV with the increasing A1 content. The SEM analysis reveals that the grain size became smaller evidently when the A1 content beyond 30% in the CIAS thin films.3. The photodetector device based on CIAS thin film was prepared and the properties were studied. The structure of photodetector device is AZO/CuIn0.78Al0.22Se2/Mo/Glass. It can be seen that the threshold voltage of device decreases and the reverse current increases sharply varying from darkness to illumination. Under the reverse bias voltage of 2 V, the photocurrent achieved 5 times amplification compared to the dark current. Fitted series resistance of photodetector is up to kiloohm, which under illumination is lower than that in darkness. Ideality factor values show a deviation between device and ideal diode. The device exhibits good spectral response in visible light, which indicates that the device based on CIAS thin film can be applied in photodetector.4. Preparation and properties of CIAS thin film solar cell. The current-voltage (Ⅰ-Ⅴ) measurements show that the CIAS thin film solar cell with Al content of 9.1% shows no photovoltaic property, while the CIAS thin film solar cell with A1 content of 6.1% exhibits photovoltaic property, and the conversion efficiency is 0.44%. It indicates that the surface roughness of absorber has significant influence on the property of solar cell. The solar cell conversion efficiency is relevant to the series resistor. The larger value of series resistor will decrease the short current of solar cell. |
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