Click to edit Master title style. The Prospects for Cost-Competitive Photovoltaics: From Nanoscale Science to Macroscale Manufacturing

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Nelson, Manager Nanostructure Physics Department Center for

1 1 The Prospects for Cost-Competitive Photovoltaics: From Nanoscale Science to Macroscale Manufacturing Jeffrey S. Nelson, Manager Nanostructure Physics Department Center for Integrated Nanotechnologies Sandia National Laboratories Albuquerque, NM

2 2 Onsite workforce: 11,711 Regular employees: 9,238 Gross payroll: ~$981M Data for FY12 through end of September Research & Development staff(4,682) by discipline Sandia Workforce Mission Areas: Nuclear Weapons Defense Systems and Assessments Energy, Climate, and Infrastructure Security International, Homeland, and Nuclear Security 2

Sandia Workforce Mission Areas: Nuclear Weapons Defense Systems and Assessments

3 3 Solar Energy Harvesting The Sun is Everywhere A transformative PV technology should be able to take on a variety of form factors and harvesting environments, without a loss in efficiency. Our Power Needs are Everywhere Power is needed for our homes and buildings, for our ever increasing mobile unwired lifestyle, for emergency and national security situations, and for our emerging electricity based transportation sector. Current PV Technologies Can t Meet These Needs! Form factor unchanged in 30+ years

Our Power Needs are Everywhere Power is needed for our homes and buildings, for our ever increasing mobile unwired lifestyle,

4 4 Options for Reducing the Cost of PV Volume Manufacturing (Engineering) Improve (cost, yield) Manufacturing of Si and CdTe Technologies - Process improvements - Device design improvements Reduce Balance-of-System Costs - Inverters - Trackers - Optics - Installation, Permitting, MEPV Science Small Amounts of Cheap Materials - Organic films / Inorganic-Organic Hybrids - Earth Abundant TF (Cu Oxide, all Carbon ) - Nanotechnology based (Wires, Dots) Increase Efficiency - Multi-Junction III-V Cell Concentrators - Multi-Exciton Generation Physics - New Materials

MEPV Science Small Amounts of Cheap Materials - Organic films / Inorganic-Organic Hybrids - Earth Abundant TF (Cu Oxide, all Carbon ) -

5 5 Cell Technology Efficiencies MJ Cells 1J-GaAs c-si Multi c-si CdTe commercial CIGS CdTe a-si Organics QDs Others

6 6 Average Si Module Prices $4.00 M W P $2.65 $2.75 $2.65 $2.90 $3.03 $3.39 $3.50 $3.25 $2.18 $1.48 $1.25 $1.35 $3.50 $3.00 $2.50 $2.00 $1.50 $1.00 A S P $ / W p $ Est $0.00 MWp Average Selling Prices 2012 Navigant Solar Services Program, Paula Mints

7 7 Thin-Film PV CdTe 12.9% R&D Cells 18.7% Potential for High Efficiency (~20%) Cu(In x Ga 1-x )Se 2 Earth Abundant Materials (~10%, but early) Cu 2 ZnSnSe x S 4-x

8 8 Organic PV Cell Efficiencies 4-10% Reliability TBD! 12% organic solar cell efficiency

9 9 Transparent OPV Efficiency ~ 2% Transparency ~ 60%

10 10 All Carbon Solar Cell (~0.5% efficient) 300nm across The three main parts a nanotube cathode and a graphene anode sandwiching an active layer made of nanotubes and buckyballs were all made by printing or evaporating from inks. Zhenan Bao, Stanford

cathode and a graphene anode sandwiching an active layer made

core (red), intrinsic shell (yellow) and n-type shell (blue) To create the circuit, individual nanowire power cells were

11 11 Nanowire Solar Cells Image: B. Tian, Lieber Group, Harvard University ~3% efficient Scanning electron microscope image of a coaxial nanowire end with p-type core (red), intrinsic shell (yellow) and n-type shell (blue) To create the circuit, individual nanowire power cells were selected and 'clipped' using chemical etching to expose their p-type cores. The team then attached the core and the outer n-type layer to metal contacts to make a circuit and measured the solar cell's electrical properties.

12 12 Microsystems Enabled Photovoltaics Sandia is developing small, thin PV cells Based on MEMS, IC, Micro-Optics, and Electronics Assembly Technologies Cells Mini-Modules Kapton Corning Willow Glass 20x Concentrator

Micro-Optics, and Electronics Assembly Technologies

13 MEPV Technology Leverages the Semiconductor Manufacturing and Innovation Ecosystem Uses existing high-volume IC/LCD/LED/MEMS manufacturing tool sets and supply chains Uses available high-volume

13 13 MEPV Technology Leverages the Semiconductor Manufacturing and Innovation Ecosystem Uses existing high-volume IC/LCD/LED/MEMS manufacturing tool sets and supply chains Uses available high-volume polymer and glass materials supply chain Uses standard semiconductor processes and electronics assembly and packaging techniques Manufacturing cost dominated (IC, LCD) Material cost dominated (conventional PV) Integrated Circuit Market Size: $300B LCD Market Size: $102B LED Market Size: $12.5B MEMS Market Size: $10B Rajendra Singh, "Why silicon is and will remain the dominant photovoltaic material," Journal of Nanophotonics, vol. 3, (2009), p. 4.

Manufacturing cost dominated (IC, LCD) Material cost dominated (conventional PV) Integrated Circuit Market Size: $300B LCD Market Size: $102B LED Market Size: $12.

14 14 Efficiency/Potential Efficiency Silicon contribution to cost ($/Watt) Advantages of Using Small, Thin Crystalline Materials for Solar Cells Crystalline materials have much higher efficiency than non-crystalline (c-si: >20%; a-si<10%) Thin cells use much less material, leading to high Watts/gram curve knee current thickness Thickness (µm) Small, pixelated, thin cells allow highly flexible and conformal (moldable) system designs Small cells allow unique system architectures, thereby reducing the balance of systems costs

Watts/gram 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.

9% Efficient, 14um thick, 250 m diameter cell Release from handle wafer using an HF

15 15 Thin c-si PV Cell Fabrication and Performance SOI wafer Create p-n junction then anisotropically etch between cells to buried oxide layer. 14.9% Efficient, 14um thick, 250 m diameter cell Release from handle wafer using an HF based release etch. After release, the handle wafer can be reused to create a new SOI wafer. Cells on wafer Released cells

16 16 Tethered Cells For Multiple Assembly Approaches Fabrication Process CROSS SECTION FRONT VIEW A) SOI wafer with nitride and oxide Suspended Cells on Wafer Solder Bumps for Electrical Connections B) First deep etch reaching the BOX layer Anchor Cell C) Wet etch to expose the handle wafer for anchors D) Poly-silicon fill Cell Tethers Cell E) Chemical mechanical polishing F) Second deep etch defining the cell and 2nd wet etch to suspend the cell

reaching the BOX layer Anchor Cell C) Wet etch to expose the handle wafer for anchors D) Poly-silicon fill Cell

reflow process Cells on wafer with solder bumps + Receiving Substrate with Interconnects Assembly process

17 17 Silicon Cell Assembly and Module Fabrication Industry standard solder bumping used to create interconnects Large array of cells on wafer assembled and interconnected in one step Low temperature solder reflow process Cells on wafer with solder bumps + Receiving Substrate with Interconnects Assembly process compatible with many substrate types Cells after solder reflow connection to receiving substrate and removal from wafer

18 18 Flexible c-si Photovoltaics c-si on Flex-Circuit 14% mini-module efficiency High flexibility of <2mm bending radius Ultra-High power density ( 440Watts/kg). Path to increase Si module performance - efficiency to >20% - >1000 Watts/kg

radius Ultra-High power density ( 440Watts/kg).

19 19 s=50 Small MEPV Cell Size Offers Advantages in Form and Function MEPV Interconnect Network Interconnection architectures can produce application specific voltages in small areas, improved shading performance, and enhanced robustness. Series and parallel arrangements enable the system to produce energy even if punctured or torn. 10k-40k cells per sq. meter 100s of Volt operation Better shading performance Tolerance to cell failures Reconfigurable Logical Connections p=16

robustness. Series and parallel arrangements enable the system to produce energy even if punctured or torn.

20 20 Defense Land/Air/Space Applications for High-Efficient, Ultra-Flexible Photovoltaics Commercial Mobile/Logistic Terrestrial Solar Power

21 21 Efficiently Capturing Solar Energy Honsberg, 2005, proceedings, 20 th European Photovoltaic Solar Energy Conference (pg. 453)

22 at concentration of 400-1000x Most Recent Commercial State-of-the-Art Monolithic MJ Concentrator Cells

22 22 at concentration of x Most Recent Commercial State-of-the-Art Monolithic MJ Concentrator Cells Pioneers NREL SPIRE Emcore Spectrolab Sharp Fraunhofer at 418 suns 44% at 947 suns Courtesy, Dan Friedman, NREL

23 23 CPV Approaches

24 Sandia MEPV Concentrator Design Cell-Level Characteristics: Multi-junction (4-6J) cell design for increased efficiency Independent connections for all cell contacts Use wafer bonding for

24 24 Sandia MEPV Concentrator Design Cell-Level Characteristics: Multi-junction (4-6J) cell design for increased efficiency Independent connections for all cell contacts Use wafer bonding for integration of lattice mismatched designs Substrate Reuse (Si, GaAs, InP) Module System Characteristics: Moderate Concentration ( x) Micro-Optic Low Profile Concentrator Inexpensive Trackers (Flat-plate, 2-axis), Large Acceptance Angle, Refractive Micro-Lens Arrays (±2-4 ) 5 Junction, Ideal 57% InGaP 1.85 Manufacturing Approach: 3D Integration and Optoelectronic Packaging IC/MEMS Processing Technologies Molded plastic optics? Optically Transparent Bonding Layer GaAs Si ? InGaAsP InGaAs

25 25 Nor malized current (percentage of max) First MEPV Si Micro-Concentrator Prototype Performance Measurements (20.9 Suns): - First microlens array with micro-cells - 1cm module thickness (commercial concentrators are ~ 25cm thick) - Large acceptance angle of +/- 4 degrees % efficiency Current response to off axis measurements Angle off from perpendicular (degrees) cell 21 cell 113 cell 180

26 26 Thank You For the Opportunity

Solar Photovoltaic (PV) Cells

Solar Photovoltaic (PV) Cells A supplement topic to: Mi ti l S Micro-optical Sensors - A MEMS for electric power generation Science of Silicon PV Cells Scientific base for solar PV electric power generation