Engineering topics

Forrest, Stephen

Publications and source records attributed to Forrest, Stephen.

5 records

DOE OSTI2024

Organic photovoltaic device having a lateral charge transport channel

Organic photovoltaic cells (OPVs) and their compositions are described herein. In one or more embodiments, the OPV or solar cell includes a first electrode (e.g., cathode); a second electrode (e.g., anode); an active layer positioned between the first electrode and the second electrode; and a channel layer positioned between the first electrode and the active layer, wherein the channel layer is configured to laterally disperse a charge across the channel layer. In certain examples, the first electrode is arranged in a grid structure having a plurality of electrode segments and a respective opening between adjacent segments of the first electrode.

Forrest, Stephen↗

DOE OSTI2022

Organic vapor jet deposition using an exhaust

Methods and systems for organic vapor jet deposition are provided, where an exhaust is disposed between adjacent nozzles. The exhaust may reduce pressure buildup in the nozzles and between the nozzles and the substrate, leading to improved deposition profiles, resolution, and improved nozzle-to-nozzle uniformity. The exhaust may be in fluid communication with an ambient vacuum, or may be directly connected to a vacuum source.

Forrest, Stephen↗

DOE OSTI2022

Organic light-emitting devices using a low refractive index dielectric

A device including an organic light emitting diode and a dielectric layer is provided. The dielectric layer provides additional distance between a reflector and the organic emission region, leading to improved reduction in non-emissive modes and enhanced efficiency.

Forrest, Stephen↗

DOE OSTI2020

A 3D nonfullerene electron acceptor with a 9,9'-bicarbazole backbone for high-efficiency organic solar cells

One-dimensional ladder-type nonfullerene electron acceptors (NFAs) with large fused ring cores have been typically used in highly efficient organic solar cells (OSCs). Prior studies have demonstrated that small molecule acceptors with three-dimensional (3D) structures may exhibit low energy loss, and hence can lead to improved OSC performance. In this study, a new 3D NFA ( 99CZ-8F ) with a 9,9'-bicarbazole backbone was designed, synthesized, and characterized, where two linear A-D-A architectures were linked by a single N–N bond. 99CZ-8F showed strong absorption in the range of 500–800 nm in the solid state, which is complementary to the absorption of the donor material PM6 . After regulating the morphology of the active layer via binary solvent mixture, the optimized device exhibited a maximum power conversion efficiency (PCE) of 6.6 ± 0.1%, which is among the best reported values for 3D nonfullerene electron acceptor based OSCs

14 SOLAR ENERGY↗

DOE OSTI2019

Combining Fluorescence and Phosphorescence to Achieve Very Long Lifetime and Efficient White OLEDs (Final Technical Report)

The objective of our project was to develop a high efficiency, long lived WOLED using a hybrid approach to harvesting singlet and triplet excitons, as described above. WE met out GONOGO metric at the end of year one, achieving an efficiency of nearly 50 lm/W for high quality white light emission. We faced an unforeseen problem in achieving this high efficiency level at high brightness. Our hybrid devices showed a significant roll off in device efficiency as the current is raised, such that our efficiency dropped to ca. 10 lm/W at 1000 nits. This roll off precluded us form achieving our send year targets with regards to efficiency at high brightness and long device lifetime. We spent the majority of our efforts in year two trying to decrease or eliminate this efficiency roll off, but this roll off prevented us from reaching our end of program target of high efficiency at high brightness with long device lifetime. Toward the end of the sixth quarter of the program we began to investigate a new approach, which involved a tandem WOLED, with a hybrid blue/red OLED stacked on a phosphorescent green OLED. The resultant emission from the stack will be white and the tandem structure relaxes the constraints on the materials, which we believe is key issue in the high roll off in efficiency.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗