Like any new technology, solid-state lighting must demonstrate a compelling value to buyers before it begins to win sizeable market share from the incumbent technologies it will replace. Over the past decade, research and development have yielded impressive improvements in the cost, color performance, light output, efficacy, reliability, lifetime, and manufacturability of SSL products. Looking at LED packages specifically, the cost in dollars per kilolumen ($/klm) has been declining rapidly since 2005 at a rate of around 20% per year. As a result, some LED lighting products have become competitive with their conventional counterparts in the marketplace for certain applications.
Despite the rapid pace of its development, solid-state lighting has not yet come close to achieving its full potential. Significant work remains to be done to further improve performance and reduce costs.
Light-Emitting Diodes (LEDs)
LEDs are semi-conductor devices that produce light when an electrical current flows through them, and are based on inorganic (non-carbon-based) materials. Optimizing efficiency in LED lighting will hinge on ongoing improvements to light-generating materials (LEDs and phosphors) and system integration. The LED package remains a significant cost component for many luminaires, but prices in terms of $/klm are declining rapidly. One package-integration direction has been to increase light output from a given package size to decrease cost, while another has been to drive LED material at lower current densities and use lower-cost packaging materials. There are still many challenges that need to be met in order to achieve DOE's efficacy goals. For example, better green and red LEDs can reduce phosphor conversion losses and enable color control. In addition, we still need to improve aspects such as color quality, light distribution, reliability, dimming, thermal management, and driver and power supply performance.
Organic Light-Emitting Diodes (OLEDs)
OLEDs are based on organic (carbon-based) materials. Unlike LEDs, which are small point sources, OLEDs are made in sheets that provide a diffuse-area light source. While developing rapidly, OLED technology is less mature than LED technology, and innovations are still needed on multiple fronts to increase the efficiency, lifetime, and output of OLED devices. The development of device architectures and materials systems (particularly blue) that allow for improved stability and efficiency, and methods to extract the light generated by the OLED, remain key challenges.
In addition to increasing the performance of devices, OLED costs need to be simultaneously reduced. Manufacturing technology developments and infrastructure investments will be essential to enable price reductions and transition OLED products from the prototype stage to commercial viability. By improving the yield (panel-to-panel color, brightness consistency) and reliability (premature failure rate) through improved manufacturing processes, costs could be lowered considerably. Another route to decreasing production costs is the development of roll-to-roll manufacturing capabilities using printing deposition processes, which may allow for high materials usage efficiency and throughput. What’s more, roll-to-roll manufacturing is well-suited for processing on flexible substrates, and a key differentiating feature of OLEDs is their ability to operate as flexible or conformable devices.
Leveraging the flexibility and other distinctive qualities of OLEDs—e.g., thin, lightweight, large-area, diffuse light source—to create novel luminaires is another key challenge. The purpose of such luminaire concepts is to spur the adoption of OLEDs, promoting consumer interest and familiarity with the technology and generating revenue for continued R&D investment.
Industry Input Guides SSL R&D Agenda
The DOE SSL R&D Program is guided by the DOE SSL R&D Plan. All funding opportunity announcements (FOAs) and project selections align with this document, which is updated annually in collaboration with industry partners.