Significance of Ambient Temperature Control for Highly Reproducible Layered Perovskite Light-Emitting Diodes

Abstract

Achieving high reproducibility in materials properties of perovskites is critical to the reliable development of optoelectronic device applications such as photovoltaics and light-emitting diodes. However, it can be difficult to obtain reproducible and optimized performance from these materials, particularly for reduced-dimensional perovskites, because different 2D/quasi-2D perovskite layer numbers have similar formation energies. Here, we report that variations in the exact ambient temperature during solution processing, even in the small range of 21–31 °C, as may occur during the day or across seasons, influence the formation and crystallographic orientation of Ruddlesden–Popper phase perovskites with a formula of PEA2MA n–1Pb n Br3n+1. We find that growth at a lower ambient temperature (∼21 °C) predominantly favors low-n phases of the perovskite, especially n = 1 with an orientation parallel to the substrate. Conversely, higher ambient temperatures (∼26 and 31 °C) yield a larger fraction of high-n phases with a vertical orientation and suppressed the formation of the low-n phases. We show that the coexistence of parallel and perpendicular orientations leads to improvements in the electrical and photophysical properties, and consequently improved light-emitting device performance. Furthermore, higher ambient temperatures affect the surface morphology through the formation of cubic grains. Consequently, the precise ambient temperature yields a relative standard deviation of 9.9% for maximum luminance, while uncontrolled temperature causes a high relative standard deviation of 71.4%. These findings highlight the importance of ambient temperature control during processing of layered perovskites. We anticipate that this study should help the field of optoelectronic device research improve the reproducibility in the fabrication of low-dimensional perovskite-based devices.

Optimization of Composition with Reduced Phase Impurity in Quasi‐2D Perovskite for Electroluminescence

“…With the variation of the thickness of the emissive layer from 60 to 325 nm, we could demonstrate the maximum efficiency for 100 nm thick perovskite film with a current efficiency of 15.4 cd A −1 and an EQE of 4.3%, in agreement with recent reports with a similar emissive material. [ 21,24,27,28 ] The thickness of the emissive layer for this n = 3 quasi‐2D perovskites in the range of 100–170 nm is found to be optimal thickness with improved charge carrier balance. Furthermore, an increase in the emissive layer thickness results in a low EQE of around 1% due to charge carrier imbalance (Figure 4d).…”

“…A device with an emissive layer thickness of 100 nm has the highest LE value of ≈15.4 cd A −1 and an EQE of 4.3% (Figure 4 and Table 1 ), in agreement with recent reports for such systems. [ 21,24,27,28 ] Furthermore, an increase in an emissive layer thickness to 220 and 325 nm shows a decrease in EQE despite higher relative PL can be due to an imbalance of charge carriers. Hence, the thickness in the range of 100–170 nm seems to be optimal for n = 3 quasi‐2D perovskites (Figure 4a,b).…”

“…[ 13,16 ] Higher phase impurity can result in inefficient energy transfer, and emission comes from individual phases rather than only the lowest bandgap phase. [ 17–19 ] Phase impurity can be controlled via having slight modulation of stoichiometric composition, [ 9 ] non‐stoichiometric compositions, [ 20 ] use of additive, [ 14 ] change of processing environment, e.g., ambient temperature variation, [ 21 ] thickness variation of the active layer, spin speed, change of host solvent, [ 22 ] and method of deposition. [ 23–25 ]…”

“…Still, PeLEDs with moderate EQE values of around 5% were also published recently, where in‐depth analysis has been carried out for perovskite layer composition as well as charge injection layers. [ 21,24,27,28 ] In general, the conventional p‐i‐n or n‐i‐p device structure with one electron injection layer and one hole injection layer (HIL) is insufficient for efficient PeLEDs. An additional hole or electron layer can help in achieving better efficiency of PeLEDs.…”

Assessing the Impact of Ambient Fabrication Temperature on the Performance of Planar CH3NH3PbI3 Perovskite Solar Cells

“…This temperature is most commonly that found inside the glove box and can vary throughout the day and across seasons by around 10°C. In 2020, the group of Han et al [20] demonstrated that the performance of perovskite based light emitting diodes (LEDs) depended on the ambient temperature over a range of 21-31°C. These authors observed different crystallographic orientation of the Ruddlesden-Popper phase perovskites with the formula of PEA 2 MA n-1 Pb n Br 3n-1 whose formation depends on the temperature in the glovebox during the solution processing.…”