1THIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

1

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

THIRD GENERATION PV: TANDEM JUNCTION

“The fuel in the earth will be exhausted in a thousand or more years, and its mineral wealth, but man will find substitutes for these in the winds, the waves, the sun's heat, and so forth.” – John Burroughs (1916)

ONWUKWE, EMMANUEL A. ID#: 40399 STREAM: MSc. PHYCOOPER, KOLLIE LACKAY ID#: 40447 STREAM: MSc. MSE NUMFOR, LINDA BIH ID#: 40416 STREAM: MSc. MSE

COURSE INSTRUCTOR: PROF. ESIDOR NTSOENZOK

2

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

OUTLINE

INTRODUCTION VARIOUS APPROACHES

DESIGN OF EFFICIENT TANDEMPROSPECTS AND

CONCLUSION

Motivation Aim and Objectives 3rd Generation PV : Goal

Fundamentals, description

Multi junction (Tandems) Multiple carrier excitation Hot Carriers Other Approaches

Efficiency evaluation Design ConsiderationDesign constraints Material Selection Final design and evaluation

3

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real World 4THIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

INTRODUCTIONMOTIVATION

4

The energy system at the beginning of the 21st century is characterized by over six billion people that live on the Earth with a total energy consumption of approximately 13 TW.

Electrical energy which represents about 12% of all energy consumed worldwide is widely used for industrial and household applications though some 2 billion people do not have access to electricity.

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

Fig 1.0 An overview of today’s energy sourcesSource: Horazak, D.A , Brushwood, J.S (2010)

Fig 1.1 Electricity generation and consumption inToday’s energy systemSource: Horazak, D.A , Brushwood, J.S (2010)

5

The direct conversion of solar radiation into electricity is often described as a photovoltaic (PV) energy conversion because it is based on the photovoltaic effect - the generation of a potential difference at the junction of two different materials in response to visible or other radiation.

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

6

WHY THE LOW PERCENTAGE OF 0.01% IN PV CONSUMPTION?• Relative High Efficiency though less than

Shockley-Quiesser limit of 33.7%• Extremely high cost dominated by

material costs of silicon wafer, glass cover sheet and encapsulant

• significantly decreased material cost but compromised efficiency badly <15%

Calculations based on thermodynamics demonstrate that the limit on the conversion efficiency of sunlight to electricity is 93% as opposed to the upper limit of 33% for a single junction solar cell, such as a silicon wafer and most present thin-film solar cells – hence need for 3rd generation.

Conversion efficiency has to be increased substantially in order to progress further.

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

AIM AND OBJECTIVES

7

AIM: To design and present an efficient third generation PV namely a tandem junction

THROUGH THE FOLLOWING OBJECTIVES(1)A detailed discussion of the goal, fundamental and description of the third generation photovoltaics

(2)A detailed consideration of the various approaches used to achieve third generation PV while paying attention to their description, and advantages, disadvantages .

(3) Achieve an optimal design by relevant design considerations and implementation.

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

3RD GENERATION PV

8

GOAL:The main goal of the third generation materials is the improvement of poor electrical performances of second generation materials while keeping low production costs with clear targets of 30-60% efficiency.

Statistics indicate that costs are targeted to decrease to well below the $1/W level of second-generation PVs to $0.50/W, potentially to $0.20/W or better, by significantly increasing efficiencies but maintaining the economic and environmental cost advantages of thin-film deposition techniques

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

FUNDMENTALS/ DESCRIPTION:

9

Increasing efficiency strongly leverages lower costs because the smaller area required for a given power also reduces balance-of-systems costs, such that efficiency values well above 30% could dramatically decrease these costs per Watt.

The fundamental process is to circumvent the Shockley-Queisser limit for single-bandgap devices through multiple energy thresholds

Fig. 1.3  Efficiency and cost projections for first- (I), second- (II), and third- generation (III) PV technologies Source: Conibeer, G (2007)

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

10

The fundamental description of the third generation is built by identifying the loss mechanisms in a standard solar cell and seeking out ways to reduce them

(1) Non absorption of below band gap photons

(2) Lattice thermalization loss

(3) Junction and contact voltage loss

(4) Junction and contact voltage loss

(5) Recombination loss

Fig. 1.3  Loss Mechanism in standard Solar cellsSource: Conibeer, G (2007)

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

11

VARIOUS APPROACHESMULTIJUNCTIONS (TANDEMS)

Dec

reas

ing

Ba

nd g

ap

Suggested by Jackson in 1955 approach increases energy level by stacking of P-N junctions in different semiconductor materials

Fig. 2.1  Schematic of Tandem CellsSource: Conibeer, G (2007)

Highest tandem efficiency is by optimizing power in each cell through appropriate choice of:MATERIAL SYSTEM• bandgap

• Thickness

• Junction depth

• Doping characteristics

CONFIGURATION

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

Fig. 2.2  Configurations for tandems Source: Arizona State university series (2009)

MATERIAL SYSTEMIII-V ALLOYSTHIN FILMSa-SiSi Nanostructure

CONFIGURATION

12

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

13

CONCENTRATED PV

ADVANTAGES(1) Ultra-high efficiencies are often in concentrators (2) the voltage-to-current ratio increases, thus decreasing

resistive losses in the high current densities of concentrator cells

DISADVANTAGES(3) They make the overall more complex and less modular.(4) They require direct sunlight, hence do not work with overcast

sky.

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

14

MULTIPLE CARRIER EXCITATION

Carriers generated from high-energy photons (at least twice the bandgap energy) absorbed in a semiconductor can undergo impact ionization events resulting in two or more carriers close to the bandgap energy

A device based on this approach requires a means of allowing the multiple electron-hole pairs to be separated, transported, and collected in a bulk structure. This is the subject of ongoing research

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

15

HOT CARRIERSThe final option for increasing efficiencies is to allow absorption of

a wide range of photon energies but then to collect the photogenerated carriers before they have a chance to thermalize

The concept underlying hot carrier solar cells is to slow the rate of photoexcited carrier cooling, which is caused by phonon interaction in the lattice, to allow time for carriers to be collected while they are still at elevated energies (‘hot’).

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

16

OTHER APPROACHES

QUANTUM ANTENNAThe idea of a quantum antenna is to use the wave nature of light

rather than its particle nature. In-coming light waves oscillate electrons in an antenna tuned to the wavelength of light – hence the devices have to be of the order of a few hundred nanometers. Maximum achievable efficiency is 48%

THERMOPHOTONICThermophotonics is a variation in which the thermal source heats

a luminescent diode similar to the TPV cell, this then illuminates the cell with a spectrum strongly peaked just above their common bandgap. These approaches would normally use waste heat from an industrial process or similar and hence not be PV, but they can be coupled to an emitter heated by solar thermal energy

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

17

DESIGN OF AN EFFICIENT TANDEMEFFICIENCY EVALUATION

Fig. 4.1  Junction and Efficiencies (Arizona State university series (2009)

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

18

DESIGN CONSIDERATION

High efficiency requires the realization of solar cells with specified band gaps, and each solar cell requires nearly ideal properties. – Means that must be able to make each solar cell with high minority carrier lifetime

THUS MAJOR DESIGN CONSTRAINTS ARE:

(1)Series connection

(2) Band Gap and lattice Matching

DESIGN CONSTRAINTSHigh efficiency requires the realization of solar cells with specified band gaps, and each solar cell requires nearly ideal properties. – Means that must be able to make each solar cell with high minority carrier lifetime

THUS MAJOR DESIGN CONSTRAINTS AFFECTING MATERIAL SELECTION:

(1)Series connection

(2) Band Gap and lattice Matching

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

19

CONCENTRATED VS UNCONCENTRATED (Major consideration cost)

OPTICAL CHOICE

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

20

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

21

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

22

FINAL DESIGN AND EVALUATION

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

23

PERSPECTIVEHigher junction tandems ranging from 5 junctions and above are theoretical said not to exceed the maximum of 86.8 % under concentration. The verification of this is the perspective for future studies.

Multicarrier excitation and Hot carrier cells as two different approaches to 3rd generation realization has not been fully realized and is a perspective for future consideration.

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

24

CONCLUSIONThird generation tandem cells is the technology to improve efficiency and maintain low production cost of photovoltaic cells as the efficiency is increased the cost is further reduced.

We have discussed several approaches to achieve them with an efficient design of a 4 Junction tandem presented.

© 2010 Pearson Education South Asia Pte LtdPhysical Chemistry 2nd EditionChapter 16: The Particle in the Box and the Real WorldTHIRD GENERATION PV: TANDEM JUNCTION MSE COURSE: MATERIALS FOR ENERGY AND STORAGE ©2015 Onwukwe E.A, Cooper K.L, Numfor, L.B

25

REFERENCES

ACKNOWLEDGEMENT

Lecture series Prof Esidor

Galvin Conibeer (2007) Third Generation Photovoltaics. Materials today, Volume 10, Issue 11, page 42-50

Advanced Solar Cells lecture series, Arizona state University (2009)

Special thanks to our lecturer, Prof. Esidor and my colleagues too numerous to mention.