真空闪蒸法制备钙钛矿薄膜的光学性质研究

Optical Properties of Perovskite Films Fabricated by Vacuum Flash Method

近年来,以有机无机杂化铅卤钙钛矿为吸光层的薄膜太阳能电池受到了广泛的关注,不到十年时间其光电转换效率已经从3.8%提高到了23%,这主要归因于有机铅卤钙钛矿材料光吸收系数高,带隙合适并易于调控,电子-空穴扩散长度长等优点。2016年Gr?tzelL等人利用低气压快速去除薄膜前驱体溶剂的方法,获得了高质量的甲脒和溴离子掺杂钙钛矿薄膜。相比于其他传统的溶液制备方法,这种方法能够很好的解决大面积均匀性的问题,为高效率、大面积钙钛矿太阳电池产业化提供了可能。钙钛矿薄膜的成份、结构及其光学性能对于太阳电池的器件性能起决定性作用,因此在该制备技术下,研究不同掺杂种类钙钛矿薄膜对光学性质的影响具有积极的意义。利用真空闪蒸溶液技术制备了3种成分的钙钛矿薄膜,利用扫描电镜、 X射线衍射,吸收光谱和荧光光谱等表征手段对薄膜的形貌、结构和光学性质进行了研究。结果表明,该技术可以用于制备均匀致密、无针孔的高质量甲脒、溴离子掺杂和氯离子掺杂的钙钛矿薄膜(成分分别为(FAPbI3)0.85(MAPbBr3)0.15,MA3PbI3和MAPb(IxCl1-x)3),薄膜中晶粒的尺寸分别为500, 100和200 nm左右;薄膜的形成过程为溶剂中的DMSO与钙钛矿配位,并在真空闪蒸过程中快速形成相对稳定中间相,经过加热后,薄膜中的DMSO被去除并形成钙钛矿晶体,结构为四方相;甲脒、溴离子和氯离子掺杂的薄膜对可见光有强烈的吸收作用,薄膜吸收边均在750 nm左右;薄膜的掺杂对带隙宽度没有明显影响, 3种成份的薄膜带隙宽度位于1.6 eV左右;甲基胺碘化铅的荧光发射峰在765 nm,甲脒和溴离子掺杂后发光峰位红移至774 nm,氯离子掺杂后薄膜峰位处于761 nm,有微弱的蓝移,且强度出现下降。这可能是晶粒尺寸和薄膜内部缺陷变化导致的。

In recent years, thin film solar cells with perovskite materials as light absorbers have attracted increased attention. The power conversion efficiencies(PCE) of organic lead-halide perovskite solar cells have reached 23% in ten years, resulting from perovskite absorber material with high absorption coefficient, suitable and adjustable bandgap, long carrier diffusion length. In 2016, Gr?tzelL introduced a simple vacuum-flash solution processing method(VFSP) to obtain FA and MA mixed perovskite film with high quality. Compared with other traditional solution processing methods, VFSP paved the way to realize high-PCE and large-area perovskite solar cells. In this work, the perovsikte films were fabricated by VFSP, and scanning electron microscopy(SEM), X-ray diffraction(XRD), absorption and photoluminescence spectra were used to investigate the morphology, structure and optical properties. The results showed that this method can be used to prepared uniform and pinhole-free perovskite films with FA-, Br and Cl-doping, including(FAPbI3)0.85(MAPbBr3)0.15, MAPbI3 and MAPb(IxCl1-x)3. The crystal grain sizes were 500, 100 and 200 nm, respectively. The growing process of the film was that the intermediate-phase was formed during the vacuum-flash process, and then turned into perovskite phase after annealing. The films had strong absorption in the visible region, and the absorption edges were about 750 nm. The optical absorption edge(Eg) values of the films with different compositions were about 1.6 eV. The PL intensity of the film with Cl-doping decreased and the peak showed a blue-shift compared to MAPbI3 film, which might be caused by the increase of the grain size and the reduction of the defect density.