Heterointerface control of organic semiconductor devices
Lead Research Organisation:
University of Cambridge
Department Name: Physics
Abstract
Organic electronic materials are widely used in LEDs, transistors and, though less advanced, in solar cells. Organic semiconductor devices are generally divided into two classes: those made by vacuum deposition of so-called 'small molecules' and those made by solution-processing of film-forming materials (typically polymers). The UK community, following some of the early work at Cambridge has tended to concentrate on the latter class of materials. The rationale for this is two-fold. Firstly, in terms of translation to large-scale manufacture, direct low-temperature solution processing of active semiconductors is very attractive for low-cost processing, particularly where patterning can be carried out by direct printing (ink-jet printing has been developed, for example, for deposition of red-, green- and blue-emitting materials in full colour displays). Secondly, solution processing presents challenges and opportunities for the formation of useful device structures. In some respects it is awkward - it is generally difficult to assemble multiple layers of organic semiconductor to make conventional laminar heterostructures because solvents are typically not sufficiently specific to allow successive layer depositions without disturbing lower layers - but in other respects, there are real opportunities to generate architectures that would be very difficult to make conventionally. For example, interpenetrating networks of electron-accepting and hole-accepting polymers are required for photovoltaic devices, so that light absorbed throughout the thickness of the semiconductor layer can generated excitons close enough to a region of heterojunction to generate separated charges. The rapid progress made over the last 10 years has taken the field to a level where device performance already sustains a fledgling industry. Basic understanding of the electronic structure of organic heterointerfaces both underpins this industry, and also presents us with a new landscape for discovery where we need to achieve a new level of control over molecular and nanoscale structure. Limitations in current device performance, for LEDs, PVs and FETs, are determined by limitations in our ability to control and measure structures at heterointerfaces. The vision of the present project is to achieve a step-change improvement in the control of molecular and nanoscale structure at organic heterointerfaces and thus to bring about a step-change in electronic functionality and performance of active semiconductor devices including LEDs, FETs and photovoltaics .The mining of this rich new seam of science will deliver game-changing discoveries for both science and engineering. The programme encompasses a variety of different interfaces, between organic-organic and organic-inorganic semiconductors; organic semiconductors and dielectrics; and organic semiconductor-electrode interfaces.
Publications
Hallam T
(2009)
Local charge trapping in conjugated polymers resolved by scanning Kelvin probe microscopy.
in Physical review letters
Sakanoue T
(2010)
Band-like temperature dependence of mobility in a solution-processed organic semiconductor.
in Nature materials
Fei Z
(2011)
Comparative Optoelectronic Study between Copolymers of Peripherally Alkylated Dithienosilole and Dithienogermole
in Macromolecules
Reid O
(2011)
The influence of solid-state microstructure on the origin and yield of long-lived photogenerated charge in neat semiconducting polymers
in Journal of Polymer Science Part B: Polymer Physics
Elmalem E
(2011)
Chain-Growth Suzuki Polymerization of n-Type Fluorene Copolymers
in Macromolecules
Mulherin RC
(2011)
Ternary photovoltaic blends incorporating an all-conjugated donor-acceptor diblock copolymer.
in Nano letters
Müller C
(2011)
Enhanced Charge-Carrier Mobility in High-Pressure-Crystallized Poly(3-hexylthiophene)
in Macromolecules
Jamieson F
(2012)
Fullerenecrystallisation as a key driver of charge separation in polymer/fullerene bulk heterojunction solar cells
in Chem. Sci.
Zhong H
(2012)
Air-stable and high-mobility n-channel organic transistors based on small-molecule/polymer semiconducting blends.
in Advanced materials (Deerfield Beach, Fla.)
Kronemeijer AJ
(2012)
A selenophene-based low-bandgap donor-acceptor polymer leading to fast ambipolar logic.
in Advanced materials (Deerfield Beach, Fla.)
Friedel B
(2012)
Enhanced nanoscale imaging of polymer blends by temperature-controlled selective dissolution.
in Small (Weinheim an der Bergstrasse, Germany)
Fei Z
(2012)
Near Infrared Absorbing Soluble Poly(cyclopenta[2,1-b:3,4-b']dithiophen-4-one)vinylene Polymers Exhibiting High Hole and Electron Mobilities in Ambient Air
in Chemistry of Materials
Gwinner MC
(2012)
Highly efficient single-layer polymer ambipolar light-emitting field-effect transistors.
in Advanced materials (Deerfield Beach, Fla.)
Shahid M
(2012)
Photovoltaic and field effect transistor performance of selenophene and thiophene diketopyrrolopyrrole co-polymers with dithienothiophene
in Journal of Materials Chemistry
Lu L
(2012)
Barium Hydroxide as an Interlayer Between Zinc Oxide and a Luminescent Conjugated Polymer for Light-Emitting Diodes
in Advanced Functional Materials
Sommer M
(2012)
Synthesis, Purification, and Characterization of Well-Defined All-Conjugated Diblock Copolymers PF8TBT- b -P3HT
in Macromolecules
Elmalem E
(2012)
Synthesis and photophysics of fully p-conjugated heterobis-functionalized polymeric molecular wires via Suzuki chain-growth polymerization.
in Journal of the American Chemical Society
Ehrler B
(2012)
In situ measurement of exciton energy in hybrid singlet-fission solar cells.
in Nature communications
Kohn P
(2012)
On the role of single regiodefects and polydispersity in regioregular poly(3-hexylthiophene): defect distribution, synthesis of defect-free chains, and a simple model for the determination of crystallinity.
in Journal of the American Chemical Society
Bakulin AA
(2012)
The role of driving energy and delocalized States for charge separation in organic semiconductors.
in Science (New York, N.Y.)
Eggeman AS
(2013)
Measurement of molecular motion in organic semiconductors by thermal diffuse electron scattering.
in Nature materials
Zhong H
(2013)
Low band gap dithienogermolodithiophene copolymers with tunable acceptors and side-chains for organic solar cells
in Journal of Materials Chemistry A
Westacott P
(2013)
On the role of intermixed phases in organic photovoltaic blends
in Energy & Environmental Science
Musser AJ
(2013)
Activated singlet exciton fission in a semiconducting polymer.
in Journal of the American Chemical Society
Walker B
(2013)
Singlet exciton fission in solution
in Nature Chemistry
Rao A
(2013)
The role of spin in the kinetic control of recombination in organic photovoltaics.
in Nature
Kohn P
(2013)
Crystallization-Induced 10-nm Structure Formation in P3HT/PCBM Blends
in Macromolecules
Wilson MW
(2013)
Temperature-independent singlet exciton fission in tetracene.
in Journal of the American Chemical Society
Yau C
(2013)
Influence of the Electron Deficient Co-Monomer on the Optoelectronic Properties and Photovoltaic Performance of Dithienogermole-based Co-Polymers
in Advanced Functional Materials
Koch F
(2013)
The impact of molecular weight on microstructure and charge transport in semicrystalline polymer semiconductors-poly(3-hexylthiophene), a model study
in Progress in Polymer Science
Böhm M
(2014)
The Influence of Nanocrystal Aggregates on Photovoltaic Performance in Nanocrystal-Polymer Bulk Heterojunction Solar Cells
in Advanced Energy Materials
Deschler F
(2014)
High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors.
in The journal of physical chemistry letters
Sepe A
(2014)
Structure formation in P3HT/F8TBT blends
in Energy Environ. Sci.
Watanabe S
(2014)
Polaron spin current transport in organic semiconductors
in Nature Physics
Asil D
(2014)
Role of PbSe Structural Stabilization in Photovoltaic Cells
in Advanced Functional Materials
Fei Z
(2014)
Influence of side-chain regiochemistry on the transistor performance of high-mobility, all-donor polymers.
in Journal of the American Chemical Society
Chow PC
(2014)
Nanosecond intersystem crossing times in fullerene acceptors: implications for organic photovoltaic diodes.
in Advanced materials (Deerfield Beach, Fla.)
Gélinas S
(2014)
Ultrafast long-range charge separation in organic semiconductor photovoltaic diodes.
in Science (New York, N.Y.)
Gao F
(2014)
Trap-induced losses in hybrid photovoltaics.
in ACS nano
Etherington M
(2014)
Recombination pathways in polymer:fullerene photovoltaics observed through spin polarization measurements
in Applied Physics Letters
Venkateshvaran D
(2014)
Field-effect modulated Seebeck coefficient measurements in an organic polymer using a microfabricated on-chip architecture
in APL Materials
Sadhanala A
(2014)
Preparation of Single-Phase Films of CH3NH3Pb(I1-xBrx)3 with Sharp Optical Band Edges.
in The journal of physical chemistry letters
Venkateshvaran D
(2014)
Approaching disorder-free transport in high-mobility conjugated polymers.
in Nature
Athanasopoulos S
(2014)
Field-enhanced recombination at low temperatures in an organic photovoltaic blend
Elmalem E
(2014)
Mechanically strong, fluorescent hydrogels from zwitterionic, fully p-conjugated polymers
in Chem. Commun.
Morgenstern FS
(2014)
Ultrafast charge- and energy-transfer dynamics in conjugated polymer: cadmium selenide nanocrystal blends.
in ACS nano
Poletayev AD
(2014)
Triplet dynamics in pentacene crystals: applications to fission-sensitized photovoltaics.
in Advanced materials (Deerfield Beach, Fla.)
Tabachnyk M
(2014)
Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals.
in Nature materials
Description | A major focus for chemical synthesis was the challenge of producing in-chain heterojunctions between different conjugated polymer blocks, in order to achieve efficient long-range charge separation. Considerable progress was made in improved polythiophene synthesis, and in making block copolymers using polythiophene as one on the blocks. Materials characterisation using microscopy and diffraction produced important advances in the understanding, particularly, of the ordering of donor-acceptor bulk heterojunctions used in solar cells. Thus, the morphology of polythiophene/fullerene blends were found to be controlled by crystallisation. New transient optical spectroscopic techniques were developed that enabled measurements of bound and unbound donor-acceptor charge transfer states. Using electrical transport, charge modulation optical spectroscopy (CMS), Raman spectroscopy and theoretical simulations we developed a detailed understanding of the influence of dynamic molecular lattice fluctuations on the charge transport physics of molecular semiconductors. We undertook a detailed scanning Kelvin probe microscopy study of charge transport in chain-extended structures of pBTTT, which identified charge trapping in grain boundaries between the chain-extended crystalline regions as the main bottleneck for charge transport. In order to study the spin transport physics of organic materials we developed a ferromagnetic resonance based spin pumping technique to inject pure spin currents into conjugated polymers from an adjacent inorganic ferromagnet. With improved design of charge injecting source and drain electrodes we have been able to realize light-emitting field effect transistors with very high external quantum efficiencies. We achieved high values of polymer LED efficiency (for a singlet-emitting OLED), reaching 47 cd/A with an index-matched sphere. Single junction photovoltaic cells are limited in their theoretical maximum efficiency by their mismatch with the broad solar spectrum, as understood by the Shockley-Quiesser relation, to around 33%. An approach to overcome this limitation is to use a material that can split the initial photoexcited state into two excitations that both generate electron-hole charge pairs. We have shown, in a series of publications, that some organic semiconductors, particularly pentacene, can show very efficient conversion of the spin singlet exciton generated by light absorption into two spin triplet excitons of about half the energy each of the singlet. We have further demonstrated that this can be combined with an inorganic semiconductor (nano crystalline lead selenide) which can capture the lower photon energy fraction of the solar spectrum within the same device. In principle, this demonstrates the feasibility of exceeding the SQ limit within a single junction solar cell. Towards the end of the grant we studied the properties of the lead halide perovskite structure materials recently found by the group of Henry Snaith in Oxford to show excellent solar cell performance. Using fabrication techniques adapted from those used for organic semiconductors we succeeded in making light-emitting diodes (red and green) using these materials, in collaboration with the Oxford group. This work shows potential for commercial development and was taken further using an EPSRC Impact Acceleration Account Follow-On Grant. |
Exploitation Route | Results for organic LEDs, solar cells and FETs have been used to develop improved organic electronic technologies in a number of UK-based companies. |
Sectors | Electronics,Energy |
Description | The emerging results from this project have provided important understanding and new direction for organic electronic devices. This includes enhanced efficiency of solar cells, enhanced efficiency of organic LEDs and enhanced mobility of charge carriers in organic semiconductor FETs. |
First Year Of Impact | 2010 |
Sector | Education,Electronics |
Description | Impact Acceleration Account Follow-On Fund |
Amount | £58,324 (GBP) |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 09/2014 |
End | 06/2015 |
Title | Pressure-Induced Amorphisation And A New High Density Amorphous Metallic Phase In Matrix-Free Ge Nanoparticles: Simulation Data |
Description | The folder contains: -Pseudopotential files for Ge and H in the .recpot format used in all calculations. -Input and output files for constant enthalpy geometry relaxations of hydrogenated Ge nanocrystals using the electronic enthalpy method within ONETEP (version 3.3). -Input and output files for the DFPT calculations performed with CASTEP (version 6.01). |
Type Of Material | Database/Collection of data |
Year Produced | 2015 |
Provided To Others? | Yes |
Title | Research data supporting "Efficient singlet exciton fission in pentacene prepared from a soluble precursor" |
Description | Underlying datasets for all figures in the Manuscript and the SI. Data comprises results from absorption-, photoluminescence-, ellipsometry-, transient spectroscopy-, FTIR-, X-ray and atomic force microscopy measurements. |
Type Of Material | Database/Collection of data |
Year Produced | 2016 |
Provided To Others? | Yes |