1

PV prospects: thinPV prospects: thin--film cellsfilm cells

LECTURE 8

• Si cell costs

• optimizing conversion efficiency

• thin-film cells

• Schottky-barrier theory

22

Silicon materialSilicon material

X

XXX

X

Metallurgical grade Si

Semiconductor grade Si Si + 3HCl SiHCl3 + H2

3SingleSingle--crystal Si modulescrystal Si modules

44

Thin scThin sc--Si solar cellsSi solar cells

10X reduction in Si use claimedK.J. Weber et al., IEEE Photovoltaic Specialists Conf., 991-994, 2005.

55

mcmc--Si solar cellsSi solar cells

“The lowest retail price for a multi-crystalline silicon solar module is $1.74 per watt (€1.29 per watt) from a US retailer.”

http://www.udel.edu/igert/pvcdrom/index.html

http://www.solarbuzz.com/Moduleprices.htm

6Cost of PV modulesCost of PV modules

The lowest retail price for a multicrystalline silicon solar module is $1.61 per watt (€1.13 per watt) from a US retailer. The lowest retail price for a monocrystallinesilicon module is $1.48 per watt (€1.04 per watt), from an Asian retailer. Brand, technical attributes, and certifications do matter. The lowest thin film module price is at $1.40 per watt (€0.98 per watt) from a US-based retailer.

http://www.solarbuzz.com/Moduleprices.htm

7Alternatives to limitedAlternatives to limited--area Si: thinarea Si: thin--film cellsfilm cells

Requirements:

• near optimum bandgap

• direct bandgap

• long minority carrier lifetime

• abundant material

• large-area-deposition capability

8Efficiency and Efficiency and bandgapbandgap

CIGSCdTe

Why is there a maximum in the relationship?

UMTD [Sec. 7.5.1]

9Optimum Optimum bandgapbandgap

10SolarSolar--cell efficienciescell efficiencies

Sarah Kurtz NREL/PR-520-46924

11CIGS and CIGS and CdTeCdTe: thin: thin--film contendersfilm contenders

Noufi and Zweibel, IEEE 4th World conf on PEC, 317-320, 2006

12Commercial Commercial CdTeCdTe: First Solar: First Solar

“Before First Solar's manufacturing innovations, cadmium-telluride photovoltaic cells were the size of postage stamps; now the company makes them as big as window panes.”

http://spectrum.ieee.org/energy/renewables/first-solar-quest-for-the-1-watt

13Towards commercial CIGS: Towards commercial CIGS: NanosolarNanosolar

NREL Certifies 15.3% Nanosolar Foil Efficiency

By Nanosolar Communications - September 9, 2009

http://www.nanosolar.com/technology

14Examination of CIGS cellsExamination of CIGS cells

• Vacancy doping of CIGS

• The role of the CdS film

• The role of the ZnO/ITO layers

• Replacement of CdS/ZnO/ITO with a Schottky barrier

Noufi and Zweibel, IEEE 4th World conf on PEC, 317-320, 2006

15

no grading

graded composition of Ga near front.