Colorful, bandgap-tunable, and air-stable CsPb(IxBr1-x)(3) inorganic perovskite films via a novel sequential chemical vapor deposition

Recently, the emerging inorganic perovskites CsPbX3 (X = Br, I) have received great attention in the photovoltaic community due to their excellent photoelectric property and good thermal stability. However, most of the reported CsPbX3 films are fabricated by the uncontrolled solution method, and it is challenging to generate pinhole-free Br-rich films due to the over-rapid liquid-phase reaction feature and the solubility limitation of bromide. Herein, we develop a sequential chemical vapor deposition (CVD) method to fabricate colorful, bandgap tunable, and stable CsPb(IxBr1-x)(3) films. First, air-stable CsPbBr3 precursor films are fabricated via a Br-2-assisted CVD process. Second, a series of CsPb(IxBr1-x)(3) (x = 0, 0.2, 0.33, 0.5, 0.67, 0.8, 1) high-quality films with consistent compositions are then obtained by another MAI/MABr-assisted CVD process. Experimental results show that all of the CsPb(IxBr1-x)(3) films have the same cubic structure and (100) preferred orientation. With the increase of MAI component, the colors of films darken gradually, the main diffraction peaks at (100) and (200) planes shift to small angle, their optical bandgaps monotonously decrease from 2.34 eV to 1.67 eV, the grains of films grow up, and the porous films become more compact. Strikingly, it is found that CsPb(IxBr1-x)(3) films become very stable in air ambient when x is less or equal to 0.5. Therefore, we first employ a cost-effective CVD technology to modulate the anion compositions of CsPbX3 inorganic perovskite films, which shows a high potential for the photovoltaic applications such as highly efficient tandem perovskite solar cells (PSCs) and colorful smart photovoltaic windows.