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Investigating the Influence of Interfacial Contact Properties on Open Circuit Voltages in Organic Photovoltaic Performance: Work Function Versus Selectivity

Journal Article · · Advanced Energy Materials
The role of work function and thermodynamic selectivity of hole collecting contacts on the origin of open circuit voltage (VOC) in bulk heterojunction organic photovoltaics is examined for poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT) and [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) solar cells. In the absence of a charge selective, electron blocking contact, systematic variation of the work function of the contact directly dictates the VOC, as defined by the energetic separation between the relative Fermi levels for holes and electrons, with little change in the observed dark saturation current, J0. Improving the charge selectivity of the contact through an increased barrier to electron injection from the fullerene in the blend into the hole contact results in a decreased reverse saturation current (decreased J0 and increased shunt resistance, RSH) and improved VOC. Based on these observations, we provide a set of contact design criteria for tuning the VOC in bulk heterojunction organic photovoltaics.
Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Interface Science: Solar Electric Materials (CISSEM)
Sponsoring Organization:
USDOE SC Office of Basic Energy Sciences (SC-22)
DOE Contract Number:
SC0001084
OSTI ID:
1382304
Journal Information:
Advanced Energy Materials, Journal Name: Advanced Energy Materials Journal Issue: 5 Vol. 3; ISSN 1614-6832
Publisher:
Wiley
Country of Publication:
United States
Language:
English

References (76)

The origin of the open-circuit voltage in polyfluorene-based photovoltaic devices journal October 2002
Charge carrier photogeneration and decay dynamics in the poly(2,7-carbazole) copolymer PCDTBT and in bulk heterojunction composites with PC 70 BM journal March 2010
Light intensity dependence of open-circuit voltage of polymer:fullerene solar cells journal March 2005
Recombination Dynamics as a Key Determinant of Open Circuit Voltage in Organic Bulk Heterojunction Solar Cells: A Comparison of Four Different Donor Polymers journal August 2010
Fluorinated alkyl phosphonic acid SAMs replace PEDOT:PSS in polymer semiconductor devices journal March 2012
Built-In Potential in Conjugated Polymer Diodes with Changing Anode Work Function: Interfacial States and Deviation from the Schottky–Mott Limit journal April 2012
Stability of Polymer Solar Cells journal December 2011
On the origin of the open-circuit voltage of polymer–fullerene solar cells journal October 2009
Using Self-Assembling Dipole Molecules to Improve Charge Collection in Molecular Solar Cells journal January 2006
Design Rules for Donors in Bulk-Heterojunction Solar Cells—Towards 10 % Energy-Conversion Efficiency journal March 2006
Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells journal March 2010
Selective Interlayers and Contacts in Organic Photovoltaic Cells journal May 2011
Recombination in polymer-fullerene bulk heterojunction solar cells journal December 2010
Molecular Understanding of the Open-Circuit Voltage of Polymer:Fullerene Solar Cells journal November 2011
Interface Energetics and Level Alignment at Covalent Metal-Molecule Junctions: π-Conjugated Thiols on Gold journal May 2006
Molecular Adjustment of the Electronic Properties of Nanoporous Electrodes in Dye-Sensitized Solar Cells journal October 2005
The Energy of Charge‐Transfer States in Electron Donor–Acceptor Blends: Insight into the Energy Losses in Organic Solar Cells journal June 2009
Tuning the Effective Work Function of Gold and Silver Using ω-Functionalized Alkanethiols: Varying Surface Composition through Dilution and Choice of Terminal Groups journal October 2009
Molecular Adsorption on ZnO(101̅0) Single-Crystal Surfaces: Morphology and Charge Transfer journal July 2012
Production Aspects of Organic Photovoltaics and Their Impact on the Commercialization of Devices journal January 2005
Modification of the Surface Properties of Indium Tin Oxide with Benzylphosphonic Acids: A Joint Experimental and Theoretical Study journal November 2009
Cathode dependence of the open-circuit voltage of polymer:fullerene bulk heterojunction solar cells journal November 2003
Anode Interfacial Tuning via Electron-Blocking/Hole-Transport Layers and Indium Tin Oxide Surface Treatment in Bulk-Heterojunction Organic Photovoltaic Cells journal February 2010
Phosphonic Acid Modification of Indium−Tin Oxide Electrodes: Combined XPS/UPS/Contact Angle Studies journal April 2008
Upscaling of polymer solar cell fabrication using full roll-to-roll processing journal January 2010
Interface materials for organic solar cells journal January 2010
Charge Formation, Recombination, and Sweep-Out Dynamics in Organic Solar Cells journal January 2012
Surface composition, work function, and electrochemical characteristics of gallium-doped zinc oxide journal June 2012
Characterization of Indium−Tin Oxide Interfaces Using X-ray Photoelectron Spectroscopy and Redox Processes of a Chemisorbed Probe Molecule:  Effect of Surface Pretreatment Conditions journal January 2002
Determination of Quasi-Fermi Levels across Illuminated Organic Donor/Acceptor Heterojunctions by Kelvin Probe Force Microscopy journal September 2011
Bimolecular recombination losses in polythiophene: Fullerene solar cells journal September 2008
Offset energies at organic semiconductor heterojunctions and their influence on the open-circuit voltage of thin-film solar cells journal March 2007
Enhanced Power Conversion Efficiency in PCDTBT/PC70BM Bulk Heterojunction Photovoltaic Devices with Embedded Silver Nanoparticle Clusters journal August 2011
Inverted Polymer Solar Cells Integrated with a Low-Temperature-Annealed Sol-Gel-Derived ZnO Film as an Electron Transport Layer journal February 2011
Evidence for near-Surface NiOOH Species in Solution-Processed NiO x Selective Interlayer Materials: Impact on Energetics and the Performance of Polymer Bulk Heterojunction Photovoltaics journal November 2011
Origin of the Open Circuit Voltage of Plastic Solar Cells journal October 2001
Enhanced Efficiency in Plastic Solar Cells via Energy Matched Solution Processed NiOx Interlayers journal July 2011
Low-temperature, solution-processed molybdenum oxide hole-collection layer for organic photovoltaics journal January 2012
Comparing organic to inorganic photovoltaic cells: Theory, experiment, and simulation journal March 2003
Transient photocurrent measurements of PCDTBT:PC 70 BM and PCPDTBT:PC 70 BM Solar Cells: Evidence for charge trapping in efficient polymer/fullerene blends journal April 2011
The Binding Energy of Charge-Transfer Excitons Localized at Polymeric Semiconductor Heterojunctions journal March 2011
Organic/metal interfaces in self-assembled monolayers of conjugated thiols: A first-principles benchmark study journal October 2006
Limits of open circuit voltage in organic photovoltaic devices journal March 2010
Origin of the open-circuit voltage in multilayer heterojunction organic solar cells journal November 2008
Analytical model for the open-circuit voltage and its associated resistance in organic planar heterojunction solar cells journal April 2008
Energy level alignment in PCDTBT:PC70BM solar cells: Solution processed NiOx for improved hole collection and efficiency journal May 2012
Bulk heterojunction solar cells with internal quantum efficiency approaching 100% journal April 2009
Characterization of the Interface Dipole at Organic/ Metal Interfaces journal July 2002
Polymer-Fullerene Bulk-Heterojunction Solar Cells journal April 2009
Physics of Solar Cells book January 2005
The Nanoscale Morphology of a PCDTBT:PCBM Photovoltaic Blend journal April 2011
Energy Level Alignment and Interfacial Electronic Structures at Organic/Metal and Organic/Organic Interfaces journal June 1999
Phenylphosphonic Acid Functionalization of Indium Tin Oxide:  Surface Chemistry and Work Functions journal July 2006
Toward Control of the Metal−Organic Interfacial Electronic Structure in Molecular Electronics:  A First-Principles Study on Self-Assembled Monolayers of π-Conjugated Molecules on Noble Metals journal April 2007
Theoretical study of the surface modification of indium tin oxide with trifluorophenyl phosphonic acid molecules: impact of coverage density and binding geometry journal January 2010
The Interface Energetics of Self-Assembled Monolayers on Metals journal June 2008
Small-molecule solar cells—status and perspectives journal September 2008
Molecular and Morphological Influences on the Open Circuit Voltages of Organic Photovoltaic Devices journal July 2009
Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy journal March 2008
The Modification of Indium Tin Oxide with Phosphonic Acids: Mechanism of Binding, Tuning of Surface Properties, and Potential for Use in Organic Electronic Applications journal October 2011
Efficient, Air-Stable Bulk Heterojunction Polymer Solar Cells Using MoOx as the Anode Interfacial Layer journal April 2011
Fantastic plastic journal May 2008
Solution deposited NiO thin-films as hole transport layers in organic photovoltaics journal August 2010
Origin of open circuit voltage in planar and bulk heterojunction organic thin-film photovoltaics depending on doped transport layers journal August 2008
Influence of the hole-transport layer on the initial behavior and lifetime of inverted organic photovoltaics journal May 2011
S-shaped current-voltage characteristics of organic solar devices journal September 2010
Spatially Modulating Interfacial Properties of Transparent Conductive Oxides: Patterning Work Function with Phosphonic Acid Self-Assembled Monolayers journal September 2011
Ultrafast Exciton Dissociation Followed by Nongeminate Charge Recombination in PCDTBT:PCBM Photovoltaic Blends journal June 2011
MoO3 Films Spin-Coated from a Nanoparticle Suspension for Efficient Hole-Injection in Organic Electronics journal October 2010
Exciton Formation, Relaxation, and Decay in PCDTBT journal December 2010
Surface Composition and Electrical and Electrochemical Properties of Freshly Deposited and Acid-Etched Indium Tin Oxide Electrodes journal October 2007
Impact of contact evolution on the shelf life of organic solar cells journal January 2009
Organic Solar Cell Efficiencies Under the Aspect of Reduced Surface Recombination Velocities journal November 2010
Influence of cathode oxidation via the hole extraction layer in polymer:fullerene solar cells journal May 2011
Optimum mobility, contact properties, and open-circuit voltage of organic solar cells: A drift-diffusion simulation study journal April 2012
The effect of carrier mobility in organic solar cells journal April 2010