Reduced Defects of MAPbI₃ Thin Films Treated by FAI for High‐Performance Planar Perovskite Solar Cells

Abstract

Organolead trihalide perovskite films with a large grain size and excellent surface morphology are favored to good-performance solar cells. However, interstitial and antisite defects related trap-states are originated unavoidably on the surfaces of the perovskite films prepared by the solution deposition procedures. The development of post-growth treatment of defective films is an attractive method to reduce the defects to form good-quality perovskite layers. Herein, a post-treatment tactic is developed to optimize the perovskite crystallization by treating the surface of the one-step deposited CH 3 NH 3 PbI 3 (MAPbI 3 ) using formamidinium iodide (FAI). Charge carrier kinetics investigated via time-resolved photoluminescent, open-circuit photovoltage decay, and time-resolved charge extraction indicate that FAI post-treatment will boost the perovskite crystalline quality, and further result in the reduction of the defects or trap-states in the perovskite films. The photovoltaic devices by FAI treatment show much improved performance in comparison to the controlled solar cell. As a result, a champion solar cell with the best power conversion efficiency of 20.25% is obtained due to a noticeable improvement in fill factor. This finding exhibits a simple procedure to passivate the perovskite layer via regulating the crystallization and decreasing defect density.

Surface Engineering of All‐Inorganic Perovskite Quantum Dots with Quasi Core−Shell Technique for High‐Performance Photodetectors

“…Further, when FAI concentration exceeds to 2 mg mL −1 (see device D), the performance of FAI‐treated photodetectors decline, and the reason is that the excess FAI remained in the film, in this way, excess cations in perovskite crystal increases nonradiative energy transfer to the trap‐states, thus affecting the performance negatively. [ 2,27 ] Therefore, all these findings suggest that the 1 mg mL −1 of FAI salt doping in colloidal perovskite CQDs can effectively passivate the surface defects, to enhance the light absorption capability, to prolong the carriers' life, and to improve colloidal crystallinity, consequently the device performance can be enhanced. The device performance in this work and those related work reported previously are summarized in Table S1, Supporting Information.…”

“…These results suggest that a small amount of FAI was added into the CsPbBr 3 perovskite and the composition of the films changes a little and then CsFAPbBr 3‐x I x is formed. [ 2 ] The peak at 12° for 2 mg mL −1 is associated with FAI. [ 30 ] The intensity of (110) and (200) peaks for FAI doped perovskite film (quasi core−shell) shows strongest peak in the XRD patterns (see Figure 3b and Figure S1, Supporting Information), providing the evidence for the improved crystalline quality in the FAI‐doped samples as compared with pristine film and bilayer film.…”

“…Metal halide perovskites with common formula ABX 3 , where A is monovalent cation (methylammonium (MA), formamidinium (FA), or inorganic alkali metal cesium (Cs)), B is divalent cation (e.g., lead), and X is a halide anion (i.e., Cl, Br, and I), [ 1 − 4 ] have offered the immense potential as both light‐emitting and light‐absorbing direct‐band solution‐processed semiconductors. Organic−inorganic perovskites have been widely investigated in past few years, and have been extensively studied in the field of solar cells, light‐emitting diodes, and photodetectors [ 2,5,6 ] for their superior photoelectric properties. [ 4,7 ] Under the environmental stress, however, phase dissociation with organic−inorganic perovskites and volatile nature of organic species significantly restrict their commercial applications.…”

“…quasi core−shell QDs technique, and then ligand‐exchange it by injecting FAI salt into the CsPbBr 3 CQDs solution. [ 2,15 ] By changing the dopant concentration, the electronic properties of QDs can be exquisitely controlled, and the strong quantum confinement can lessen the band tailing in perovskites QDs. In this way, all the problems raised in bilayer technique can be successfully tackled with quasi core−shell QDs technique.…”

Organic‐Inorganic Halide Perovskites: From Crystallization of Polycrystalline Films to Solar Cell Applications

“…Some additives are often used to passivate the perovskite layer in order to stablilize the ion and suppress ion migration, as shown in Figure g. Thiourea is used to passivate the perovskite layer by the formation of Pb‐S, which stabilizes the energy of perovskite structure .…”