Evolution of Structure and Optoelectronic Properties During Halide Perovskite Vapor Deposition

Abstract

The efficiency of perovskite-based solar cells has increased dramatically over the past decade to as high as 25%, making them very attractive for commercial use. Vapor deposition is a promising technique that potentially enables fabrication of perovskite solar cells on large areas. However, to implement a large-scale deposition method, understanding and controlling the specific growth mechanisms are essential for the reproducible fabrication of high-quality layers. Here, we study the structural and optoelectronic kinetics of MAPbI 3 , employing in-situ photoluminescence (PL) spectroscopy and grazing-incidence small/wideangle X-ray scattering (GI-SAXS/WAXS) simultaneously during perovskite vapor deposition. Such a unique combination of techniques reveals MAPbI 3 formation from the early stages and uncovers the morphology, crystallographic structure, and defect density evolution. Furthermore, we show that the nonmonotonous character of PL intensity contrasts with the increasing volume of the perovskite phase during the growth, although bringing valuable information about the presence of defect states.

Pizza Oven Processing of Organohalide Perovskites (POPOP): A Simple, Versatile and Efficient Vapor Deposition Method

“…Furthermore, intensity tests of the X-ray beam and laser excitation were made to exclude any detrimental influence (observer effect) on the in situ monitoring. The X-ray fluence was 10 8 photons/cm 2 /s, two orders of magnitude below 10 10 suggested by Held et al [19] to prevent degradation and well below the 10 16 decomposition threshold reported by Svanström et al [22] We did not observe a degradation by illumination either, by comparing the evolution under continuous and discontinuous (30s off, 5s on) light illumination, Figure S12 (Supporting Information). Note, the in situ experiments were conducted with a temperature setpoint at 170°C, enabling a slightly decelerated reaction, allowing for more precise tracking and a faster heating to setpoint, despite the smaller heater.…”

“…are reflected in differences in the crystallographic and optoelectronic properties. We sought to follow the evolution from template to perovskite by making use of the in situ capabilities of GIWAXS, [18] and combining it with optoelectronic insights from photoluminescence monitoring, as proposed by Mrkyvkova and Held et al [19][20][21] The reaction chamber for the in situ setup is designed to mimic the reference chamber closely, yet one notable difference between the setups is the temperature profile. To exclude artefacts introduced hereby, we compared films reacted with different temperature profiles, either with a progressive heating profile or the reference flat temperature profile in Figure S11 (Supporting Information) after the same reaction times.…”

“…In other in situ monitoring of perovskite growth, this PL behavior marks the perovskite nucleation featuring highly emissive perovskite clusters, as confirmed by X-ray diffraction. [19,[25][26][27] . In our case, identification of GIWAXS perovskite signal in stage two is made complicated by three factors: the much lower X-ray fluence (chosen to minimize observer ef-fect), the departure from grazing incidence broadening the signal (due to thermal expansion of the holder) and intrinsic geometrical broadening due to measurement conditions.…”

“…Two factors influence the position of the photoluminescence emission: changes in perovskite cluster size (with an inversely proportional relationship, cf. quantum confinement) [19,26,27,30] and halide exchange (more iodine incorporation decreases the bandgap). Regarding the fading quantum confinement effect redshifting the bandgap in stage 2, an estimation of the perovskite cluster size using Brus' equation [31] gives a monotonic increase from 8 to 21 nanometers of the perovskite cluster diameter during this stage (cf.…”

Substoichiometric Mixing of Metal Halide Powders and Their Single-Source Evaporation for Perovskite Photovoltaics

“…In situ GIWAXS allows tracking of the formation, fluctuation, and disappearance of the different crystalline phases during evaporation, as well as their orientation with respect to the substrate for the thin films once deposited. Readers interested in this technique are referred to the work of Held et al or the review of Qin et al Energy-dispersive X-ray spectroscopy (EDX) complements this structural information with chemical insights. The resulting metal halide templates are then converted into perovskite thin films and implemented in photovoltaic devices.…”