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Stephen R. Forrest

Bio: Stephen R. Forrest is an academic researcher from University of Michigan. The author has contributed to research in topics: OLED & Organic semiconductor. The author has an hindex of 148, co-authored 1041 publications receiving 111816 citations. Previous affiliations of Stephen R. Forrest include Bell Labs & Office of Technology Transfer.


Papers
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Journal ArticleDOI
10 Sep 1998-Nature
TL;DR: In this article, a host material doped with the phosphorescent dye PtOEP (PtOEP II) was used to achieve high energy transfer from both singlet and triplet states.
Abstract: The efficiency of electroluminescent organic light-emitting devices1,2 can be improved by the introduction3 of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the singlet spin states induce fluorescent emission; these represent a small fraction (about 25%) of the total excited-state population (the remainder are triplet states). Phosphorescent dyes, however, offer a means of achieving improved light-emission efficiencies, as emission may result from both singlet and triplet states. Here we report high-efficiency (≳90%) energy transfer from both singlet and triplet states, in a host material doped with the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) (PtOEP). Our doped electroluminescent devices generate saturated red emission with peak external and internal quantum efficiencies of 4% and 23%, respectively. The luminescent efficiencies attainable with phosphorescent dyes may lead to new applications for organic materials. Moreover, our work establishes the utility of PtOEP as a probe of triplet behaviour and energy transfer in organic solid-state systems.

7,023 citations

Journal ArticleDOI
29 Apr 2004-Nature
TL;DR: The future holds even greater promise for this technology, with an entirely new generation of ultralow-cost, lightweight and even flexible electronic devices in the offing, which will perform functions traditionally accomplished using much more expensive components based on conventional semiconductor materials such as silicon.
Abstract: Organic electronics are beginning to make significant inroads into the commercial world, and if the field continues to progress at its current, rapid pace, electronics based on organic thin-film materials will soon become a mainstay of our technological existence. Already products based on active thin-film organic devices are in the market place, most notably the displays of several mobile electronic appliances. Yet the future holds even greater promise for this technology, with an entirely new generation of ultralow-cost, lightweight and even flexible electronic devices in the offing, which will perform functions traditionally accomplished using much more expensive components based on conventional semiconductor materials such as silicon.

4,967 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host was described.
Abstract: We describe the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host. These devices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A) and 31 lm/W, respectively. At 100 cd/m2, the external quantum and power efficiencies are 7.5% (26 cd/A) and 19 lm/W at an operating voltage of 4.3 V. This performance can be explained by efficient transfer of both singlet and triplet excited states in the host to Ir(ppy)3, leading to a high internal efficiency. In addition, the short phosphorescent decay time of Ir(ppy)3 (<1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m2.

3,594 citations

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host, achieving a maximum external quantum efficiency of 19.0±1.0 and luminous power efficiency of 60±5 lm/W.
Abstract: We demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate [(ppy)2Ir(acac)] doped into 3-phenyl-4(1′-naphthyl)-5-phenyl-1,2,4-triazole, a maximum external quantum efficiency of (19.0±1.0)% and luminous power efficiency of (60±5) lm/W are achieved. The calculated internal quantum efficiency of (87±7)% is supported by the observed absence of thermally activated nonradiative loss in the photoluminescent efficiency of (ppy)2Ir(acac). Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of (ppy)2Ir(acac) coupled with balanced hole and electron injection, and triplet exciton confinement within the light-emitting layer.

3,302 citations

Journal ArticleDOI
TL;DR: In this paper, the double heterojunction was proposed to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved, and a full optical and electrical analysis of the double-heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials.
Abstract: In this review, we discuss the physics underlying the operation of single and multiple heterojunction, vacuum-deposited organic solar cells based on small molecular weight thin films. For single heterojunction cells, we find that the need for direct contact between the deposited electrode and the active organics leads to quenching of excitons. An improved device architecture, the double heterojunction, is shown to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved. A full optical and electrical analysis of the double heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials. Combining the double heterostructure with novel light trapping schemes, devices with external efficiencies approaching their internal efficiency are obtained. When applied to an organic photovoltaic cell with a power conversion efficiency of 1.0%±0.1% under 1 sun AM1.5 illuminati...

2,722 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: Recent advances at the intersection of plasmonics and photovoltaics are surveyed and an outlook on the future of solar cells based on these principles is offered.
Abstract: The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

8,028 citations

Journal ArticleDOI
10 Sep 1998-Nature
TL;DR: In this article, a host material doped with the phosphorescent dye PtOEP (PtOEP II) was used to achieve high energy transfer from both singlet and triplet states.
Abstract: The efficiency of electroluminescent organic light-emitting devices1,2 can be improved by the introduction3 of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the singlet spin states induce fluorescent emission; these represent a small fraction (about 25%) of the total excited-state population (the remainder are triplet states). Phosphorescent dyes, however, offer a means of achieving improved light-emission efficiencies, as emission may result from both singlet and triplet states. Here we report high-efficiency (≳90%) energy transfer from both singlet and triplet states, in a host material doped with the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) (PtOEP). Our doped electroluminescent devices generate saturated red emission with peak external and internal quantum efficiencies of 4% and 23%, respectively. The luminescent efficiencies attainable with phosphorescent dyes may lead to new applications for organic materials. Moreover, our work establishes the utility of PtOEP as a probe of triplet behaviour and energy transfer in organic solid-state systems.

7,023 citations

Journal ArticleDOI
19 Sep 2013-Nature
TL;DR: It is shown that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.
Abstract: Many different photovoltaic technologies are being developed for large-scale solar energy conversion. The wafer-based first-generation photovoltaic devices have been followed by thin-film solid semiconductor absorber layers sandwiched between two charge-selective contacts and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport positive and negative charges in spatially separated phases. Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices. Here we show that nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapour-deposited perovskite as the absorbing layer can have solar-to-electrical power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). This demonstrates that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.

7,018 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a comprehensive, up-to-date compilation of band parameters for the technologically important III-V zinc blende and wurtzite compound semiconductors.
Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

6,349 citations