Summer Sprout Develops Deep Red Phosphorescent OLED Emitters for Automotive Lighting. Potential Competitor to Universal Display

Published August 26, 2020

One of the many important developments to come out of the SID DisplayWeek symposium was a paper by a potential competitor for Universal Display Corporation in the field of phosphorescent OLED emitters. The paper was given in session 83, OLED Displays II, and entitled Optimization of High-Performance Deep-Red OLEDs Using Tandem Structure for Automotive Lighting Application, given by Huiqing Pang of Beijing Summer Sprout Technology Co, Ltd. The paper describes Summer Sprout's development of a red phosphorescent emitter for automotive OLED lighting, and lists six authors with Huiqing Pang as the lead. Dr. Pang is identified as a Vice President of Beijing Summer Sprout Technology Co., Ltd.

Who is Summer Sprout?

Dr. Pang’s presentation starts with a description of Summer Sprout (the company’s web site identifies it by the Chinese name Beijing Xiahe Technology, translated to English as Summer Sprout). The company was founded in May 2017 in Beijing and currently has more than 100 employees, of whom more than 70 are in research and development. The company’s headquarters and R&D are in Beijing, and it has a manufacturing site in Taixing, Jiangsu province, just north of Shanghai.

Summer Sprout is set up to cover nearly the whole stack of OLED materials:

  • Hole Injection Layer (HIL) and P-dopant
  • Hole Transfer Layer (HTL)
  • Electron Blocking Layer (EBL) / prime layer
  • Hold Blocking Layer (HBL)
  • Electron Transfer Layer (ETL)
  • Red, Green, and Blue Host material
  • Red, Green, and Blue Dopant material

While there are many suppliers in the industry for most of the layers in the OLED stack, there is only a single supplier of red and green dopants, Universal Display. Summer Sprout seeks to develop and manufacture IP-protected novel OLED materials and technology. The company does have some lessons to learn in IP protection, though, since its presentation at SID contained the statement “Summer Sprout Confidential and Proprietary”, and it was presented in a public forum.

Source: Summer Sprout / SID DisplayWeek 2020

Dr. Pang did not share in her presentation, but DSCC has learned, that she and at least two other authors of paper 82.1, Ray Kwong and Sean Xia, are ex-UDC employees who worked for years at the US company. Dr. Pang is listed as an inventor on 31 US patents assigned to UDC, about 5% of the 653 patents assigned to the company per the US Patent Office database. Her co-author Ray Kwong is credited with 110 patents assigned to UDC, while Sean Xia wins the crown as an inventor of 220 patents assigned to UDC. Among the three, there is relatively little overlap in the patents, as combined at least one of them is listed on 322 out of the 653 patents assigned to UDC.

Summer Sprout’s web page indicates that the company was started with capital of CNY 100 million (US$14 million) and has built 7 brand-new materials design and synthesis laboratories and 3 analysis laboratories. Dr. Pang’s presentation says that Summer Sprout’s “estimated corporate value” is now about $300 million, a big increase over the start-up funds but a small number compared to UDC’s value of $8.7 billion as of August 19th. The company’s web site lists 86 patent applications for various countries, most in China, but 29 in the US, 2 in Germany, 3 in Korea and one in Japan.

Our sources in China indicate that the company’s first location in Beijing is Zhongguancun Science Park, which has a tax-free policy for companies with leading technology patents. Their legal representative Is Dr.Xia. The company’s registered capital is only CNY 15M ($2.1M). Most of the researchers are from leading universities in China and can apply for subsidies from the government. In 2018 the company received some funding and completed the payment of registered capital. Later that same year Summer Sprout got CNY 500M ($71M) support from the Taixing government for their manufacturing site, which has capacity for an estimated annual production in 18.9 tons of OLED lighting materials. However, this project may have been delayed as there has been little progress since April 2019.

What Did Summer Sprout Present at SID?

While the company introduction and web site indicate that Summer Sprout will pursue OLED displays, the SID paper addressed a more narrow but important market opportunity – automotive taillights. We know that Audi has used OLED taillights since 2018 on selected models. Summer Sprout described the following requirements for this application:

  • Deep red emission: CIE (x,y) = (0.70, 0.30);
  • Luminance > 2000 nits;
  • > 8000 hours operational lifetime, high/low storage, temperature, and humidity lifetime;
  • High efficiency emitter;
  • Tandem structure with efficient CGL for long lifetime, high current efficiency and small angular dependence;

The paper then describes a series of stack profiles, starting with a single emitting layer. The single-unit stack met the project goals for color point but resulted in too much emission in the infra-red region, which limits the brightness efficiency. The single-unit stack did not meet the requirement for lifetime.

Summer Sprout worked through an optimization round for a stack with two emitting layers. The so-called 2-unit stack needs optimization for HTL thickness, with some trade-off between the optimal HTL for current efficiency (CE) and the optimal HTL for external quantum efficiency (EQE). The 2-unit stack provided a substantial improvement in most performance parameters, including a 2.2x improvement in both CE and EQE and a 2.75x improvement in lifetime.

Finally, Summer Sprout developed a 3-unit stack, with more optimization of HTL layers to achieve an even greater enhancement of performance, as shown in the slide. The 3-unit stack reaches CE and EQE levels 3.5x and 3.0x that of the single-unit, respectively, and a lifetime of 21,000 hours. The second slide here shows that a main part of the efficiency gains from the 3-unit stack involve reducing the wasted emission in the very deep red and infra-red area.

Source: Summer Sprout / SID DisplayWeek 2020
Source: Summer Sprout / SID DisplayWeek 2020

The presentation next shows that the 3-unit stack can achieve the requirements for automotive lighting. High temperature lifetime test shows the 3-unit device reached LT 80 ~ 1000 hours at 85C with initial luminance of 2200 nits.

Finally, the presentation concludes by shifting away from the automotive application and discussing deep red for a general display application with the target of the BT2020 color gamut. BT2020 red has a CIE(x,y) of (0.708, 0.292) and Summer Sprout generated a single-unit top emission stack which nearly matched the BT2020 red with excellent CE and EQE and acceptable lifetime.

Source: Summer Sprout / SID DisplayWeek 2020

Summer Sprout’s paper indicates that it can develop a red phosphorescent emitter for both automotive and display applications. Does that mean that it is ready to become a direct competitor for Universal Display?

Given that Summer Sprout was presenting at SID, it would appear that the company believes that its technology does not violate any of the patents held by Universal Display. DSCC asked Universal Display to comment on Summer Sprout’s technology for phosphorescent emitters. A UDC spokesperson confirmed that Huiqing Pang did work at UDC several years ago, and that “there were many papers at SID related to R&D of phosphorescent emitters but that is not related to commercial rights. In general we do not comment on specific IP issues or questions related to 3rdparties.”

Given the concerns throughout the industry raised by the US-China trade war, and the importance of OLED to many of the display makers in China, the emergence of a company like Summer Sprout was inevitable. Universal Display has noted in its own earnings calls that China customers have purchased material ahead of demand for fear of having supplies from the US cut off. The US actions to restrict Huawei feed these fears. The development of a local source for phosphorescent OLED emitter material is thus a type of insurance policy for China’s panel makers against the possibility of having its US supplier cut off in the trade war. An insurance policy for China’s panel makers, though, could prove to be a genuine competitor to UDC. We will be watching Summer Sprout closely.

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Written by

Bob O'Brien

bob.obrien@displaysupplychain.com