Photoluminescence Enhancement in Formamidinium Lead Iodide Thin Films

Abstract

current-voltage characteristics of perovskite solar cells, an anomalous hysteresis is present. [17][18][19] This affects the stability of the power output under working conditions and leads to considerable error in evaluating real effi ciencies. This hysteresis has been speculated to originate from trapping/detrapping of charge carriers within or near the surface, ferroelectric properties of hybrid perovskite ion migration. [ 18,20,21 ] The photophysics of perovskite thin fi lms and their device performance have been shown to change upon illumination in a number of recent publications. [22][23][24][25][26][27] It was discovered that a new, red-shifted peak appears in the photoluminescence spectra of mixed-halide hybrid perovskites under 1-sun illumination. [ 23 ] The carrier diffusion length in MAPbBr 3 (Cl)-based solar cells was demonstrated to increase about 3.5 times upon laser illumination. [ 28 ] The open-circuit voltage and fi ll factor of solar cells were reported by Hu et al. to continuously increase with illumination while the short-circuit current experiences a fast increase and then a decrease upon further light exposure. [ 20 ] These illumination-induced variations of the device performance suggest that important light-induced processes are occurring in the active material. It is therefore important to study these phenomena to improve the performance and stability of hybrid perovskite photovoltaic devices.Formamidinium lead iodide (FAPbI 3 ) is a relatively, newly developed perovskite material that can potentially provide better performance than methylammonium lead iodide (MAPbI 3 ) because of its narrower bandgap, which allow absorption of photons over a broader range. [ 6,7,[29][30][31][32] Moreover, FAPbI 3 exhibits negligible hysteresis during current-voltage measurements. [ 33,34 ] In this work, the room temperature photophysical properties of FAPbI 3 thin fi lms under different environments are investigated. We observed light-induced enhancement in the photoluminescence intensity when samples are exposed to air while under continuous ultraviolet light illumination. The role of nitrogen and oxygen on the photophysical properties of the fi lm is further investigated. We demonstrated that moisture plays a fundamental role in the light-healing effect in FAPbI 3 thin fi lms. Results and DiscussionFAPbI 3 perovskite thin fi lms were deposited on FTO-coated glass substrates by spin-coating from equimolar mixtures of Formamidinium lead iodide (FAPbI 3 ) has a broader absorption spectrum and better thermal stability than the most famous methylammonium lead iodide, thus exhibiting great potential for photovoltaic applications. In this report, the light-induced photoluminescence (PL) evolution in FAPbI 3 thin fi lms is investigated. The PL intensity evolution is found to be strongly dependent on the atmosphere surrounding the samples. When the fi lm is exposed to air, its photoluminescence intensity is enhanced more than 140 times after continuous ultraviolet laser illumination for 2 h, and the average lif...

Defects engineering for high-performance perovskite solar cells

“…87 The phenomenon has been observed in perovskite solar cells with various device structures. [115][116][117] However, the significance of the light soaking effects varied between laboratories and the underlying mechanism is still under debate. One of the proposed mechanisms is that light irradiation can remove or de-activate these defects via chemical reaction, resulting in a longer PL lifetime.…”

Influence of the substrate on the bulk properties of hybrid lead halide perovskite films

“…Studies of the PL properties in air, nitrogen, and oxygen/helium environment suggest that oxygen is important for PL enhancement. 56 In fact, the role of oxygen is supported by the fact that PL intensity decreases upon white illumination in N 2 environment. 55,55,57 PL intensity enhancement upon illumination in ambient conditions has been reported and tentatively explained by a catalytic reaction induced by oxygen in inorganic SrTiO 3 thin film perovskite.…”

Exciton Recombination in Formamidinium Lead Triiodide: Nanocrystals versus Thin Films

“…Formamidinium lead triiodide in its 3D perovskite form is called α‐FAPbI 3 or “black phase” and, especially in its Cs‐ and Br‐doped variations, is one of the most popular materials for solar cell and lasing applications . Compared with the archetypal but less‐chemically durable—methylammonium lead triiodide (MAPbI 3 ) perovskite—it has a more symmetric crystal structure, absorption edge shifted toward the infrared and a better thermal stability.…”