Flexible Zinc Oxide Based TCO Films With High Mobility And Its Application In Perovskite Solar Cells

Transparent conductive oxide films(TCOs) are an important class of optoelectronic films. It simultaneously possesses excellent transparency in the range of visible light and high conductivity. Also, there is a strong reflection in the range of infrared light. So it is a kind of ideal materials for transparent electrodes, which have been widely used as the critical components of solar cells, liquid crystal displays, gas sensors, and smart glasses.In this thesis, we focus on ZnO-based TCOs and its application in perovskite solar cells.We grow Al or F doped ZnO(AZO, FZO) TCO films and metal/FZO composite films(Cu/FZO, Ag NW/FZO) by pulsed laser deposition together with thermal evaporation and hydrothermal methods for noble metal films and nanowires. Also we systematically studied their transparent conductive properties. Then Ag NW/FZO composite film was applied as transparent electrode to fabricate perovskite thin film cell and the influence of composite film TCOs on the cell performance was also studied. The main research contents and results are as follows.1. Donor doped ZnO(AZO, FZO) transparent conductive thin films were grown by PLD,and the transparent conductive properties were studied. Doped ZnO targets with Al,F-compounds as donor dopants were prepared. In order to obtain the optimal growth conditions for donor doped ZnO(AZO, FZO) films, we investigated the effect of growth factors on transparent conductive properties, such as dopant concentration, deposition pressure, and substrate temperature. Under the optimal growth conditions, the resistivity of AZO film on glass substrate is 2.6 × 10-4Ω?cm with mobility of 28.8 cm2/Vs, and higher transmittance than 85% in the whole visible wavelength. The optimal resistivity of FZO film on PET substrate is 2.02×10-3Ω?cm with carrier concentration of 2.47 × 1020cm-3, mobility of 12.5 cm2/Vs, and the transmittance is also more than 90%.2. Flexible Cu /FZO composite films were prepared by combining the PLD method and the thermal evaporation method. Various thicknesses of copper films were first evaporated on the flexible substrate, then FZO thin films were deposited on copper films for fabricating Cu /FZO composite films. Meanwhile, we studied the effects of copper layer thickness on the performance of composite electrodes. We found that the increasing copper layer thicknessdecreases the film resistivity continuously(from 4×10-3 to 2.2×10-5 Ω?cm). But, the transmittance also decreases(from 80% to 5%). Hall effect experiment results confirmed that the decline of resistivity is mainly due to the increase of carrier concentration. The increase in carrier concentration is due to the carrier injected from the copper layer to the FZO layer, for the difference of Fermi level.3. Flexible Ag NW/FZO composite films were also prepared by combining the PLD method and hydrothermal method. We investigated the effect of the length of silver nanowires,spin coating process on the transparent conductive properties of Ag NW film. The experiment results show that silver nanowires(about 60 um) is more suitable for preparing the transparent conductive film than the short silver nanowires(about 15 um). When the suspension concentration is 4mg/mL, Rs of Ag NW film is 19.2 ohm / square with light transmission rate of 90.14%, higher than that of ITO(89.8%). After FZO layer coated on Ag NW film, such composite films can keep its transparent conductive properties, and exhibit high haze value(36.5%-38%). Furthermore, it can effectively improve the film mechanical properties.4. Ag NW/FZO composite films, which possess high transparent conductive performance and high haze value, were applied as transparent electrodes for perovskite thin film cells. We assembled Ag NW/FZO/TiO2/CH3NH3PbI3/HTM/metal electrode perovskite cells by two-step method, and preliminarily explored the preparation process of the device. The efficiency of perovskite cell can increased from 2.95% to 4.1% compared with the traditional FTO based perovskite cell, which is mainly due to the high haze value. The high haze value of TCE could increase light scattering, hence increase optical path length, improve light absorption and the efficiency of solar cells.