This PDF file contains the front matter associated with SPIE Proceedings Volume 12659, including the Title Page, Copyright information, Table of Contents and Conference Committee list.

Thermally activated delayed fluorescent (TADF) OLEDs promise higher luminous efficiency than traditional OLEDs but suffer from a shorter lifetime, so identifying the degradation mechanisms is crucial to find a solution. In-depth electrical characterization of TADF devices during stressing at constant current revealed a shift in capacitance onset due to the formation of interfacial trap states. Simulations showed that this shift depends on the voltage applied before performing the C-V scan and that the emptying of trap states due to Shockley-Read-Hall recombination caused the shift.

In this article, we briefly review our recent publication on the influence of trap positions on the current density-voltage characteristics of organic semiconductor devices (PRB, 107, 1652304 [2023]). The position of traps significantly affects the total charge density and electric field in the active organic layer, consequently impacting the operating voltage of the comprising devices. Our findings showed that as the position of traps moves from the charge extraction electrode (cathode) towards the charge injection electrode (anode), the required voltage to achieve a constant current density initially increases. However, a reversed trend in the operating voltage vs. trap position is observed when the traps are present in the vicinity of the anode. We figured out that this phenomenon originates from the trap position dependence of electric field distribution.

As society's interest in beauty and wellness continues to grow, there has been a rapid expansion in the wearable device market. This growth is particularly evident in the ongoing development of healthcare devices to address the rising demand for non-invasive light treatments. Many existing devices in this field are still bulky and rely on single-point light sources, which limits their ability to uniformly treat larger areas, and can cause heat-related issues. To overcome these challenges, researchers are turning to OLED-based platforms as a promising solution [1]. OLEDs, which are predominantly used in flexible and free-form displays, are at the forefront of the next generation of display technology, and offer potential advances in the field of light treatments and wearable healthcare devices.

We demonstrate a method to control charge accumulation at the hetero interfaces of organic light-emitting diodes (OLEDs) using dipolar doping of hole transport layers (HTLs). Dipolar doping enables spontaneous orientation polarization (SOP) even in nonpolar HTLs, and consequently compensates the negative interface charge originating from SOP of the adjacent layer. This concept was applied to tris-(8-hydroxyquinolate) aluminum (Alq3) and tris (2- phenylpyridine)iridium (Ir(ppy)3)-based OLEDs. We confirmed that dipolar doping modifies the density and polarity of the net interface charge and reduces the luminescence loss due to both hole and electron accumulations via exciton polaron quenching.

QLEDs have emerged as an alternative for optoelectronic applications. However, for widespread application of QLEDs, the device efficiency is required to be improved. There is a significant energy level mismatch between the valence band of commonly used quantum dots (QDs) and the HOMO level of traditional hole transport materials (HTMs). Given the small energy level mismatch between the conduction bands of the QDs and commercial electron transport materials, charge carriers in the light-emitting layer are imbalanced. Such a charge imbalance decreases the efficiency of QLED devices, and thus it is of great importance to design novel HTL materials with small energy mismatch with the QDs. Given the numerous potential molecules in the organic space, employing expensive and time-consuming approaches based on chemical intuition and trial-and-error experimentation is practically ineffective. Thus, realizing next-generation QLEDs technologies requires a paradigm change in materials design and development. Here, we combine active learning (AL) and high-throughput quantum mechanical calculations as a novel strategy to efficiently navigate the search space in a large materials library. The AL enables a systematic material screening by accounting multiple optoelectronic properties while minimizing the number of calculations. We further evaluated the top candidates using atomistic simulations and machine learning to investigate charge mobility and thermal stability in their amorphous films. This work offers guidelines for efficient computational screening of materials for QLEDs, reducing laborious, time-consuming, and expensive computer simulations, materials synthesis, and device fabrication.

The lead-free halide-based double perovskites (Cs₂SnCl₆) have gained much attention due to its promising optoelectronic properties, non-toxic nature, and relatively better stability as compared to lead-based perovskites. In the current work, the cost-effective hydrothermal method is employed to synthesize the Bi-doped double perovskite material. Here, systematic incorporation of Bi3+ in Cs₂SnCl₆ nanocrystal is highly essential to improve the optoelectronic properties and modulate the luminescence. Here, Bi3+ is used as a dopant for host-Cs₂SnCl₆ nanocrystal and as-synthesis material preserves its cubic structures up to a certain amount of Sn4+ replacement by Bi3+. Such doped and as-synthesized perovskites are characterized in detail by using photoluminescence (PL), Ultraviolet (UV-Vis) spectroscopy, and X-ray diffraction (XRD). The PL results show that luminescence peaks around 393 nm are shifted towards the higher wavelength (lower energy) after the appropriate doping of Bi in double perovskite. The UV-Vis spectroscopy exhibits the absorption edge of the as-synthesize and Bi-doped perovskites around ~310 nm and a slight shift is observed after Bi incorporation as compared to the as-synthesized one. Also, bandgap of such perovskites lies in the range of 3.28 eV–3.62 eV. The XRD results demonstrate the diffraction peaks of the Cs2SnCl6 double perovskites at 14.55°, 24.27°, and 29.03°, which originated from the planes of (111), (220), (222) respectively. Finally, chromaticity plots (obtained from the PL) confirm the enhancement of blue luminescence due to the Bi-incorporation. Therefore, all the results confirm that highly stable Bi-doped Cs₂SnCl₆ perovskites can be a suitable candidate for fabricating several wavelength-tuneable optoelectronic devices.

Hole transport layers (HTLs) have a significant role in the performance of organic and organic-inorganic solar cells. In this experiment, we have investigated HTLs for Pb-Sn binary perovskite solar cells (PSCs) to maximize the power conversion efficiency (PCE). CuI, PTAA, and PEDOT:PSS were chosen as HTLs to fabricate the MAPb0.75Sn0.25(I0.50Br0.50)3 perovskite solar cells. The solar cells were fabricated using an inverted p-i-n structure where we used ITO/HTL/Perovskite/C60/BCP/Al materials stack. For PSCs containing CuI, PTAA and PEDOT:PSS as HTL, we obtained the PCE of 3.81%, 3.11 and 6.5%, respectively, with unchanged other experimental condition. Also, PEDOT:PSS HTL-based solar cells deliver higher short circuit current of 16.37 mA/cm2 compared to CuI and PTAA HTL based binary perovskite solar cells. For these binary PSCs, PEDOT:PSS is the best choice to maximize power conversion efficiency.

Due to the high toxicity of lead, research on new lead-free perovskite semiconductor materials with suitable optical and electronic properties has been of great interest. For this reason, rare earth halide perovskites are a promising class of materials for this purpose. Here, cesium europium bromide chloride (CsEu(ClxBr1−x)3 ) perovskite nanocrystals (NCs) with Eu2+ in the B site were successfully synthesized by a hot colloidal injection method. Different proportions of the molar ratio Cs:Eu were proposed in order to enhance the optical properties to promote a deep blue emission. High resolution TEM (HRTEM) revealed that the resulting nanoparticles were spherical shaped with an average diameter of ~ 10 nm. The electronic absorption spectra show bands peaked around 380 nm. The photoluminescence (PL) spectra of NCs excited at 393 nm exhibit bands peaked at 453 nm, 590 nm, 615 nm, and 697 nm. These PL peaks coincide with the emission of Eu3+ and Eu2+, covering the entire emission spectrum. PL spectra shows that Eu2+ induces a slight broadening in the full width at half maximum (FWHM) when higher concentration ratio is used. Moreover, the PL results shows a change in the intensity of the 615 nm peak which implies that with further introduction of Eu2+ into the lattice, changes in radiative and non-radiative recombination are obtained. This work shows that the Europium based Lead-free perovskite nanocrystals are a promising candidate for optoelectronic devices.

We present a model for designing highly efficient luminescent carbene-Gold-amide complexes, utilizing thermally activated delayed fluorescence (TADF) to achieve very high radiative rates. By extending the π-system of the carbene and amide ligands, blue-emissive complexes with photoluminescence efficiencies (ΦPL > 0.95) and fast radiative rates (kr = 4 × 106 s-1) can be created. Our compounds offer a general design approach for such complexes, minimizing the energy difference between singlet and triplet states (ΔEST) while maintaining high singlet radiative rates. These emitters are well-suited for OLED devices, and we demonstrate their suitability, exploring their effects on device stability and roll-off. Our studies reveal deep blue OLEDs, utilizing novel host materials tailored to the 2-coordinate TADF emitters.

With the vigorous development of display technology, micro light-emitting diode (Micro-LED) display has become the most potential technology in the future. Its characteristics include high resolution, long life, wide color gamut, high contrast, fast response, small pixel size and low power consumption. The technical bottleneck of Micro-LED display is the mass transfer, so we use semiconductor lithography process to replace it for much lower cost and higher production speed. We propose color conversion technology to achieve higher efficiency and light intensity than mass transfer. In this study, we used a waterproof and viscous organic material Polyvinyl Butyral Resin (PVB) as the main material to synthesize rare-earth-free color conversion luminescent materials, which contain 4-(dicyanomethylene)-2-tert-butyl-6- (1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) for red light and 3-(2-Benzothiazolyl)-7-(diethylamino) coumarin (Coumarin 6) for green light with very high quantum yield (~90%). Through semiconductor process technology, we have realized the fabrication of extremely small size 4μm × 4μm display arrays. The single-color pixel density can reach 5080 pixels per inch (PPI), and the full-color pixel density reaches up to 2540 PPI, with a display color gamut covering approximately 92.3% of the digital cinema initiatives - protocol 3 (DCI-P3) standard. This research achievement offers a promising technique for manufacturing the next generation of Micro-LED displays with extremely high PPI. These advancements in display technology bring tremendous potential for various applications, ranging from consumer electronics products to augmented reality and beyond.