Development of 4th Gen OLED Screens

High energy efficiency, long lifespan and high color purity have always been essential to the display industry. However, furthering the success of Organic Light-Emitting Diode (OLED) beyond conventional low-luminance display applications used to be hampered by the low power efficiency (PE) at high luminance.

With more than 10 years of commitment, scientists from Tsinghua University, in collaboration with domestic enterprises such as Visionox Technology Inc., have demonstrated the strategic implementation of an exceptionally high-PE, high-luminance OLED, using a phosphor-assisted thermally activated delayed fluorescence (TADF)-sensitized narrowband emission. They ultimately achieved mass production and commercial application of the fourth-generation OLED adopting phosphor-assisted TADF-sensitized fluorescence (pTSF).

Breakthrough luminance strategy

Previously, OLED technology had advanced to the third generation, and the breakthrough to high PEs was made possible by using phosphorescence and TADF emitters. However, a problem with OLEDs remained unresolved, namely the tendency for efficiency to decrease with increasing luminance, known as efficiency roll-off.

Duan Lian, a chemistry professor at Tsinghua University, recalled that in 2011, when the third-generation TADF materials from abroad had made a breakthrough, he found the weakness of TADF materials after careful research, and proposed a solution to the exclusion of high PE and high luminance — instead of using a TADF emitter, using TADF materials to sensitize the energy transfer to high-color-purity fluorophores.

Deriving from their previous work on pTSF, the Tsinghua research team unveiled a breakthrough strategy for OLEDs to fully exploit the potential of a high PE under a high luminance, which was implemented on the basis of a multiple sensitized narrowband emission from a pTSF emitting layer, constituting ternary components: a TADF sensitizing-host, a phosphor-assistant and a multiple resonance (MR) emitter.

As a consequence, pTSF devices could realize a 100 percent exciton utilization in a sub-microsecond-scale, which greatly relieved the critical issue of PE roll-off with increasing luminance, highlighting the potential for the continued success of OLEDs beyond conventional low luminance display applications.

Expanding color gamut

The team started by developing the pTSF red light, which significantly increased the lifespan of the device. However, the project was once again halted as no breakthrough was made in the key narrowband red light material.

Since the red light is hard, Duan resolutely switched the direction of R&D to green light material. The turning point came in 2019, when the team developed narrowband green fluorescent materials, a world first, solving the core compatibility problem of "bright color" and "high exciton utilization rate," making pTSF technology feasible in manufacturing, Duan said.

To promote a technology from labs to industry requires in-depth cooperation among multiple parties. The Tsinghua research team, in collaboration with material manufacturers such as Jiangsu Sunera Technology Co., Ltd. and Eternal Material Technology, developed narrowband green fluorescent materials that can be mass-produced and meet commercial specifications. Visionox was responsible for the optimization of device structure and process, to realize the mass production of the new generation of OLED screens.

Through over three years of collaboration, the research team have continuously adjusted the material combinations and formulation plans, making screens equipped with high PE pTSF devices reduce power consumption by over 12 percent and increase lifespan by 15 percent, and expanding the color gamut from the conventional DCI-P3 standard to the broader BT.2020 standard.

Industrialization of pTSF technology

However, mass production was confronted with the challenges of equipment adaptation and process optimization.

The emitting layer of the previous generation of devices was composed of two components and could be produced by a dual-source evaporation process. Li Guomeng, an expert in devices from Visionox, said that the new pTSF device consists of three components and a three-source co-evaporation process is needed.

The change of production process requires a large number of meticulous adjustments and optimizations. For example, internal layout adjustments, temperature and humidity control, and airflow parameter settings could all directly affect the stability, yield and cost of the process.

"Even though we have made a lot of preparations, the performance of mass produced pTSF devices remains unknown. Many new technologies often perform well in the laboratory, but problems arise during mass production," Li said.

After hundreds of adjustments and optimizations, Visionox completed the technology verification process in 2023. In 2024, the company further upgraded the pTSF technology, continuously improving the quality. In the fourth quarter of 2025, OLED screens based on pTSF technology had entered mass production and began to be applied to the latest domestic flagship models.

The industrialization of pTSF technology has driven the collaboration of the upstream and downstream enterprises in the fields of organic materials and evaporation equipment, an overall improvement of the domestic display industry supply chain.

Source: Science and Technology Daily