Current Status of Solar Photovoltaic Technology Platforms, - PowerPoint PPT Presentation

Current Status of Solar Photovoltaic Technology Platforms, Manufacturing Issues and Research Steve Hegedus Institute of Energy Conversion University of Delaware With assistance from IEC staff: Brian McCandless (CdTe), Bill Shafarman (CIGS) Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #1

Outline  Introduction to IEC at U of Delaware  PV trends, growth in scale, contribution to energy production  Crystalline Si PV status, baseline technology, near term focus:  New methods emitter formation, passivation and device architecture  Thin Film PV status, baseline technology and near term focus:  Cu(InGa)Se 2 : wide gap alloys, improved 2-step selenization  CdTe: higher deposition T , substrate  a-Si/nc-Si (briefly) : multijunction, collapse of the a-Si industry  Two common PV myths Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #2

Institute of Energy Conversion at U of Delaware  Founded in 1972 to perform thin-film PV research  World’s oldest continuously operating solar research facility  First 10% efficient thin film solar cell (1980)  Dept of Energy University Center of Excellence for Photovoltaic Research and Education (1992) First flexible 10% cell  Soft funded - government and industry contracts  2012 staff: 11 professional, 3 tech, 2 admin, 5 post doc, >20 grad students (4 depts) 4x4 inch  Recently rec’d $8.4M from DOE (3 year grants) minimodule Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #3

IEC Research Program Goals  Expand the fundamental science and engineering base for thin film and c-Si photovoltaics to improve performance  Transfer these technologies to large-scale manufacturing  IEC has been responsible for growth of several PV start-ups through technology transfer and validation  Provide workforce with PV scientists and engineers  >40 graduates since 1992 (PV Center of Excellence) Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #4

IEC Technology Thrust Areas  Thin film polycrystalline CuInGaSe 2 -based (CIGS) solar cells  Thin film polycrystalline CdTe solar cells  Silicon-based solar cells  Front and back contact heterojunction (a-Si/c-Si)  Thin film tandem a-Si and nc-Si Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #5

IEC Facilities: complete capability for fabrication and characterization of thin film and c-Si solar cells  Over 20 thin-film deposition systems: PECVD (vhf/rf/dc), HWCVD, PVD, Vapor Transport, sputtering, H 2 S/H 2 Se reaction, chemical bath  Materials characterization: XRD, GIXRD, VASE, EDS, SEM, AFM, AAS, XPS, FTIR, Raman, optical trans+refl, Hall effect  Device fabrication: complete capability for high efficiency solar cells: c-Si (front heterojunction and IBC), CdTe, Cu(InGa)Se 2 , a-Si  Laser and mechanical scribing for monolithic module fabrication  Device characterization: J-V, J-V-T, QE, C-V, OBIC, accelerated life stress (damp-heat, ambient, light) Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #6

The Big Picture: PV applications and achievements Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #7

PV can be installed anywhere, 10’s Watts to 100’s Megawatts Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #8

Recent worldwide achievements  Installation: 17 GW in 2010 (100% growth), 30 GW in 2011 (70% growth)  Average annual growth >50% p/y for decade  EU: PV providing 2-4% of annual electricity in Spain, Germany, Italy  May 2012 Germany received >10% from PV  On one day >40% (22 Gigawatts peak supply out of 27 GW installed)  US: 5.7 GW installed, 2 GW in CA  Over 70% of 2011 installations are ‘utility scale’ or > 100 kW  Worlds largest PV power plant 250 MW Aqua Caliente Project (CA, thin film)  Creating hundreds of thousands of jobs  400,000 in Germany; 100,000 in US  R&D, manufacturing, supply chain (materials), system design, installation Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #9

Trend in PV applications: 1990-2009  1995: PV demand driven by off-grid applications  After 1995: Innovative policy in Japan, Germany stimulated market for grid-connected residential and commercial  >2008: Asian Si modules drove down prices, increased installations  >2010: Significant growth in utility scale > 1 MW projects  2012: First year of flat or  negative growth in decades, projected to recover 2013 Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #10

Industry in turmoil: ‘roller coaster ride’  Significant consolidation, bankruptcy, closures in past 2 years  Top companies for years suddenly quit PV or bankrupt  Worldwide capacity ~ twice demand yet demand still growing  Huge excess inventory  Shrinking profits - many companies selling at loss to compete  c-Si done much better in price and efficiency than many expected, squeezing thin film start ups  Renewed emphasis on improving performance since costs so low Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #11

Brief Overview of PV Basics Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #12

What is a PV device? Direct converter of light into electricity: photons in, electrical current (DC) out Three critical processes: Light Absorption + Carrier Generation + Carrier Collection (current flow) (deliver P to load) e - V+ e - load h + h + V- charge separation Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #13

Cell efficiencies vs. bandgap E G  Record performance single junction cells vs. theoretical limit  Expect maximum performance with E G ≈ 1.5 eV  But theor eff >25% possible E G ≈ 1 – 1.8 eV a-Si/nc-Si 2J  Many thin film, III-V options Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #14

Commercial Scale PV Devices  Single crystal or multicrystalline Si wafers  Dominate market: 85-90% of sales  Solar grade Si, lower qual than IC  Module efficiency: 14-20%  Low cost Asian Si driving prices down  Thin films (1-3 µm polycrystalline or amor)  Ultimately lower cost than Silicon wafers (??)  On glass, metal or plastic foils  Diverse materials, techniques  Lower quality, imperfect crystallization, more defects  Module efficiency: 8-14%  Unique advantages in building integrated products  10-15% of market, #2 PV company is TF CdTe (First Solar) Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #15

One common PV challenge: reducing gap between champion cell and module efficiency Multi c-Si and TF CIGS both ~20% cell efficiency. But mc-Si has more mature module technology. Wolden et al, JVST-A 29 (2011) 030801 Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #16

Why efficiency matters – fixed BOS costs Levelized cost of Energy: • Lifecycle costs/energy • LCOE costs include Balance of System which scale with # modules, area • Lower eff = higher BOS$ • More rack, wiring, install $ • y-intercept is system price without module • Si modules ‘selling’ at $0.9/W Or $120/m 2 Wang et al Renewable and Sustainable Energy Rev (2011) Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #17

Crystalline Si (c-Si) Technology and Advanced Concepts Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #18

Standard commercial Si PV cell process start 900 ° C 900 ° C finish 400 ° C Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #19

Commercial Si Solar Cell, Eff ~ 15-17% Front contact (Screen printed Ag fired through SiN) Random textured F and R (~ 0.3 µm) Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #20

World record Si solar cell: PERL • PERL cell: Passivated Emitter, Rear contact Locally diffused • 2-step emitter (thin n between contact and thick n+ under contact) • UNSW, AU, 1998; very complex design, not manufacturable Cell Voc (V) Isc (mA/cm 2 ) FF(%) Eff(%) PERL 0.70 42 81 24.7 Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #21

Conflicting emitter properties: pn junction vs resistance vs absorbing ‘dead layer’ property Advantage Disadvantage Increase thickness •Reduce lateral R for •Increase absorption in current flow to Ag highly defect layer contact (photons not converted •Prevent melting Ag SP to e-h pair), lower blue metal penetrate to base QE and Jsc Increase doping •Reduce lateral R •Increase defects and •Reduce contact R with recombination (Io) so Ag or other metal grid decrease Voc Increase bandgap •Decrease absorp loss •Increase lateral •Increase band bending, resistance significantly, reduce recomb (Io) req second conductive layer ($$) Photonic Spectra Webinar “PV manufacturing and research” Hegedus 09/27/12 #22