Structural and Trap‐State Density Enhancement in Flash Infrared Annealed Perovskite Layers

Abstract

dye-sensitized solar cells. The most studied perovskite compound is methylammonium lead iodide (CH 3 NH 3 PbI 3 , MAPI), although it is not moisture resistant and may be hazardous to the environment. Lee et al. [2] showed that perovskite thin layers could be used directly for harvesting solar radiation similar to inorganic semiconductors. Since then, tremendous advances have been made in optimizing perovskite solar cells (PSCs), with power conversion efficiencies (PCE) reaching 25.5% and thus coming to the proximity of single-crystal Si solar cells with a record PCE of 26.1%.The initial difficulties in preparing homogeneous perovskite films were overcome by introducing an antisolvent technique, [3,4] in which a small amount of a nonpolar solvent is used to induce heterogeneous nucleation of perovskite films. However, the antisolvent technique is not suitable for upscaling as it relies on spincoating technology. Hence, a large number of different deposition techniques [5,6] were developed to cast perovskite thin films using scalable technologies such as spray coating, inkjet printing, slot-die coating, blade coating, vacuum thermal evaporation, etc.Another way to improve the film homogeneity and crystallinity is to induce the formation of crystalline colloidal clusters Perovskite solar cells are well-known for their high energy conversion efficiency, low-temperature processing, and cost-effective production. Flash infrared annealing (FIRA) of slot-die cast perovskite precursors offers an attractive manufacturing route using high-throughput roll-to-roll technology. Despite the recent progress in FIRA perovskite annealing, the optimal composition of the perovskite precursor is yet to be developed. Here, the effect of methylammonium chloride (MACl) on the perovskite structure and trap-state density as a function of the FIRA annealing time is investigated. In situ real-time grazingincidence wide-angle X-ray scattering (GIWAXS) is employed to monitor the perovskite layer formation during FIRA annealing with millisecond temporal resolution. In addition, the density of states in the bandgap is estimated using ex situ energy-resolved electrochemical impedance spectroscopy. Evidence is found that adding 10% MACl into the perovskite precursor solution significantly improves the crystallographic orientation of the perovskite layers while reducing the trap-state density by one order of magnitude. In addition, using time-resolved GIWAXS, the most favorable time window for the FIRA processing of perovskite films with the lowest mosaicity and trap-state density is identified. The results are of general importance for elucidating the appropriate temporal windows in complex and fast-evolving crystallization processes.

Combined in Situ Photoluminescence and X-ray Scattering Reveals Defect Formation in Lead-Halide Perovskite Films

“…Among optical methods, photoluminescence (PL) spectroscopy is commonly used, as PL efficiency is closely related to PCE. ,, However, the layer morphology and structure or the chemical composition of individual phases cannot be unambiguously determined by PL during perovskite formation. X-ray scattering methods are more suitable in this respect, − but their in situ utilization is limited in laboratory conditions. Typically, synchrotron-based scattering techniques, such as grazing-incidence small/wide-angle X-ray scattering (GI-SAXS/WAXS) , or the coplanar lab-based X-ray diffraction are employed, both having their pros and cons. , X-ray diffractometers are easily accessible, but the beam intensity might not be sufficient to detect fast processes that require short integration time.…”

Slowing the hot‐carrier cooling by an organic small molecule in perovskite solar cells

“…The corresponding line‐cut profiles in the in‐plane and out‐of‐plane directions are displayed in Figure 2B,C, respectively. It was found that two predominant scattering rings at ~1.0 and ~2.2 Å −1 , which correspond to the (1 1 0) and (2 2 0) planes of perovskite crystals, respectively 41,42 . Moreover, the relative intensities (I) of (1 1 0) and (2 2 0) in the in‐plane direction and the ratios of I (110) / I (220) for control and TDCA modified films are calculated to be 1.12 and 0.59, respectively.…”

“…It was found that two predominant scattering rings at $1.0 and $2.2 Å À1 , which correspond to the (1 1 0) and (2 2 0) planes of perovskite crystals, respectively. 41,42 Moreover, the relative intensities (I) of (1 1 0) and (2 2 0) in the inplane direction and the ratios of I (110) /I (220) for control and TDCA modified films are calculated to be 1.12 and 0.59, respectively. TDCA-treated film exhibited a relatively more preferred in-plane orientation growth in the (1 1 0) direction than the control film, implying that TDCA can promote preferential orientation and crystallization of perovskite films, 43 which could be one of the important consequences in improving final PSCs photovoltaic performance.…”

In Situ and Operando Characterizations of Metal Halide Perovskite and Solar Cells: Insights from Lab-Sized Devices to Upscaling Processes

“…Such a study used a custom-designed FIRA chamber. 280 Although some inspiring examples have been demonstrated so far comprising the investigation of MAPbI 3 , FAPbI 3 , mixedcation, and all-inorganic perovskites prepared from bladecoating and slot-die, there is a continued need for developing and using in situ and operando techniques for the characterization of scaling-relevant compositions. It is likely that MAPbI 3 will not be the best perovskite formulation for upscaling, which will possibly rely on FA-rich structures or complex alloys.…”