Presentation on theme: "Enhanced Organic Photovoltaic Cell Performance using Transparent Microlens Arrays Jason D. Myers, Sang-Hyun Eom, Vincent Cassidy, and Jiangeng Xue Department."— Presentation transcript:
Enhanced Organic Photovoltaic Cell Performance using Transparent Microlens Arrays Jason D. Myers, Sang-Hyun Eom, Vincent Cassidy, and Jiangeng Xue Department of Materials Science and Engineering University of Florida Gainesville, FL, USA
Outline Introduction – Photovoltaic technology – Organic photovoltaics – Performance limitations Enhancement concept Results – Experimental – Simulation Conclusions Images courtesy of Global Photonic Energy Corp.
Solar Energy Sunlight is an ubiquitous, clean and abundant energy source. Readily available energy source for: – Remote locations – Developing nations – Outer space
Photovoltaic Technology Organics Inexpensive substrates High-throughput processing Flexible Efficiency : 8% Inorganics Expensive processing High installation costs Efficiency: >20% (c-Si), % (thin film) Image courtesy of Konarka, Inc.
Organic Photovoltaic (OPV) Basics Active layer materials can be small molecules, polymers, inorganic nanoparticles, or blends Two different materials are required: electron donor and electron acceptor Materials are generally neat layers or intermixed Substrate Transparent Electrode Active Layers Metal Electrode Illumination Absorption 1- e -αd α = absorption coefficient d = light path length Glass or plastic
OPV Operation 1. Light Absorption - η A 2. Exciton Diffusion - η ED 3. Exciton Dissociation - η CT 4. Charge Collection - η CC Donor Acceptor hv Exciton
Fundamental Tradeoffs There is a fundamental tradeoff between light absorption and exciton diffusion/charge collection. Substrate Transparent Electrode Active Layers Metal Electrode Increase layer thickness: Light absorption Charge collection Substrate Transparent Electrode Active Layers Metal Electrode Substrate Transparent Electrode Active Layers Metal Electrode Decrease layer thickness: Light absorption Charge collection
Improvement Routes 1.Develop new active materials 2.Improve device architectures 3.Manipulate light propagation and absorption Substrate Transparent Electrode Active Layers Metal Electrode Active Layers
Microlens Arrays for OPVs Effectively increase light absorption without altering active layer path length = layer thickness (1)Refraction due to incident angle and index of refraction (2)Surface reflection into neighboring features Substrate Transparent Electrode Metal Electrode Active Layers Microlens array (2) (1) path length > layer thickness
Array Fabrication (a) (c) PS PDMS (b) PS = 100μm (d) UV-glass or SiO 2 PDMS UV-glass or SiO 2 (a) (b) Cured PDMS a)Convective self-assembly of PS microspheres b)Cure PDMS, make mold c)Scotch tape to remove spheres d)Mold optical adhesive and cure, form array Substrate Microlens Array (d) Substrate Optical Adhesive PDMS mold (c) Concave PDMS mold
Experimental Results Enhancement is more significant in regions of poor spectral response Absorption 1- e -αd If α is small, path length increase is more significant Glass ITO Aluminum CuPc C 60 BCP 30nm 60nm 8nm 80nm 100nm CuPcC 60
Results, cont. Enhancement is seen with a variety of active layer materials. Enhancement is also present at all angles of incidence. Small MoleculePolymerHybrid (CuPc/C 60 )(P3HT:PCBM)(P3HT:CdSe) Enhancement in current30%29%7% θ Glass ITO Aluminum P3HT:PCBM 80nm 100nm
Device Area Dependence Enhancement increases with device area Glass ITO Aluminum CuPc C 60 BCP 40nm 70nm 8nm 80nm 100nm Laboratory-scale devices: mm x mm Production-scale devices: cm x cm
Ray Tracing Simulations More rays are being absorbed after multiple passes through the device area Air Device ITO Glass Buffer Illumination n = 1 Lens layer, n = 1.5 n = 1.5, 0.5mm thick n = 2.0, 100nm thick n = 1.7, 100nm thick n = 1 Excellent qualitative agreement with experiment In-house code Rays fired at the stack Propagation behavior is tracked
Large Area Enhancement Larger devices allow for: 1.increased light trapping 2.multiple absorption opportunities Small area device: Large area device:
Practical Applications Lens arrays provide large-area enhancement Optical enhancement effect is not specific to one material system Soft lithography is compatible with roll-to-roll production Very promising for future development Image courtesy of Frederik Krebs
Conclusions Controlling light propagation is a viable route for enhancing organic photovoltaic device performance. Enhancement is due to increased path length in active layer Mechanisms are compatible with different active materials, and production-scale processing and device sizes.
Acknowledgements Funding: – NSF CAREER Grant – DOE SETP UF OTL Xue Group