Presentation on theme: "Jason D. Myers, Sang-Hyun Eom, Vincent Cassidy, and Jiangeng Xue"— Presentation transcript:
1 Enhanced Organic Photovoltaic Cell Performance using Transparent Microlens Arrays Jason D. Myers, Sang-Hyun Eom, Vincent Cassidy, and Jiangeng XueDepartment of Materials Science and EngineeringUniversity of FloridaGainesville, FL, USA
2 Outline Introduction Enhancement concept Results Conclusions Photovoltaic technologyOrganic photovoltaicsPerformance limitationsEnhancement conceptResultsExperimentalSimulationConclusionsImages courtesy of Global Photonic Energy Corp.
3 Solar EnergySunlight is an ubiquitous, clean and abundant energy source.Readily available energy source for:Remote locationsDeveloping nationsOuter space
4 Photovoltaic Technology OrganicsInorganicsInexpensive substratesHigh-throughput processingFlexibleEfficiency : 8%Expensive processingHigh installation costsEfficiency: >20% (c-Si), 10-20% (thin film)Image courtesy of Konarka, Inc.
5 Organic Photovoltaic (OPV) Basics SubstrateTransparent ElectrodeActive LayersMetal ElectrodeIlluminationAbsorption ≈ 1- e-αdα = absorption coefficientd = light path lengthGlass or plasticActive layer materials can be small molecules, polymers, inorganic nanoparticles, or blendsTwo different materials are required: electron donor and electron acceptorMaterials are generally neat layers or intermixed
7 Fundamental Tradeoffs There is a fundamental tradeoff between light absorption and exciton diffusion/charge collection.SubstrateTransparent ElectrodeActive LayersMetal ElectrodeSubstrateTransparent ElectrodeActive LayersMetal ElectrodeSubstrateTransparent ElectrodeActive LayersMetal ElectrodeIncrease layer thickness:Light absorption ↑Charge collection ↓Decrease layer thickness:Light absorption ↓Charge collection ↑
8 Transparent Electrode Improvement RoutesDevelop new active materialsImprove device architecturesManipulate light propagation and absorptionSubstrateTransparent ElectrodeActive LayersActive LayersActive LayersMetal Electrode
9 Microlens Arrays for OPVs (2)(1)SubstrateTransparent ElectrodeActive Layerspath length > layer thicknesspath length = layer thicknessMetal ElectrodeRefraction due to incident angle and index of refractionSurface reflection into neighboring featuresEffectively increase light absorption without altering active layer
10 Array Fabrication (a) Convective self-assembly of PS microspheres UV-glass or SiO2PDMS(a)Convective self-assembly of PS microspheresCure PDMS, make moldScotch tape to remove spheresMold optical adhesive and cure, form array(a)PSPDMS(b)(b)Cured PDMS(c)Concave PDMS mold(c)PS = 100μm(d)SubstrateMicrolens Array(d)Optical AdhesivePDMS mold
11 Enhancement is more significant in regions of poor spectral response Experimental ResultsGlassITOAluminumCuPcC60BCPAbsorption ≈ 1- e-αdIf α is small, path length increase is more significantEnhancement is more significant in regions of poor spectral responseCuPcC6080nm30nm60nm8nm100nm
12 Results, cont.Enhancement is seen with a variety of active layer materials.Enhancement is also present at all angles of incidence.Small MoleculePolymerHybrid(CuPc/C60)(P3HT:PCBM)(P3HT:CdSe)Enhancement in current30%29%7%GlassITOAluminumP3HT:PCBMθ80nm100nm100nm
13 Device Area Dependence Laboratory-scale devices: mm x mmProduction-scale devices: cm x cmGlass80nmITOCuPc40nm70nmC608nmBCP100nmAluminumEnhancement increases with device area
14 Ray Tracing Simulations AirDeviceITOGlassBufferIlluminationn = 1Lens layer, n = 1.5n = 1.5, 0.5mm thickn = 2.0, 100nm thickn = 1.7, 100nm thickIn-house codeRays fired at the stackPropagation behavior is trackedMore rays are being absorbed after multiple passes through the device areaExcellent qualitative agreement with experiment
15 Large Area Enhancement Small area device:Large area device:Larger devices allow for:increased light trappingmultiple absorption opportunities
16 Practical Applications Lens arrays provide large-area enhancementOptical enhancement effect is not specific to one material systemSoft lithography is compatible with roll-to-roll productionImage courtesy of Frederik KrebsVery promising for future development
17 ConclusionsControlling light propagation is a viable route for enhancing organic photovoltaic device performance.Enhancement is due to increased path length in active layerMechanisms are compatible with different active materials, and production-scale processing and device sizes.
18 AcknowledgementsFunding:NSF CAREER GrantDOE SETPUF OTLXue Group