Experimental and modelling studies for the growth of high quality silicon-germanium absorber layer for multi-junction

solar cell by RF magnetron co-sputtering system

SEYED AHMAD SHAHAHMADIP64797

Solar Energy Research Institute (SERI)Universiti Kebangsaan Malaysia

Supervisor: Prof. Dr. Nowshad AminProf Dato’ Dr Kamaruzzaman Sopian

Presentation Outline

1. Introduction

2. Problem Statement

3. Research Objectives

4. Methodology

5. Result and Discussion

6. Conclusion

7. Future Work and Grant Chart

Introduction: Triple-junction technology

Thin-film Si solar cells have received attention due to:

• The abundance of raw materials.• Low temperature coefficient.• Low-cost manufacturing.

Despite the many advantages of thin-film Si solar cells, their low efficiencies still present a challenge that must be overcome.

The efficiency of a single-junction amorphous Si solar panel is only 8–9%. Sanyo Solar has demonstrated the stabilized module efficiency up to 12.2% by using double-junction technology (a-Si:H/uc-Si:H). However, a module efficiency of 13% is necessary to be competitive with other solar cell technologies. Triple-junction solar cells offer an even more efficient utilization of the solar spectrum by incorporating thin component cells.

High performance cellsTo obtain the highest cell efficiency, the component cells of a triple-junction structure must be individually optimized.

Recently, Prof. Konagai s group has calculated the theoretical ′conversion efficiencies for triple-junction thin-film Si solar cells. These theoretical efficiencies were obtained by varying the bandgaps of the top and middle cells while fixing that of the Bottom cell at 1.1eV, corresponding to the bandgap of the bottom cell in a μc-Si:H system.

The highest conversion efficiency of 21.4% was obtained when the bandgaps of the top and middle cells were 2 and 1.45 eV, respectively.

Key features:

• Hydrogen dilution during intrinsic (i) layer growth.• Band-gap profiling in a-SiGe:H intrinsic layers.• Optimum matching of the component.• Highly conductive tunnel junctions.• Highly reflective textured back reflectors and quality of the

textured TCO.• Continuous deposition process.• Enhancement in current matching (intermediate reflector layers)

Top Cell (a-Si:H/a-SiC:H)

Middle Cell (uc-Si:H/ nc-Si:H/ a-SiGe:H)

Bottom Cell (uc-Si:H/ nc-Si:H/ uc-SiGe:H)

Introduction: Silicon Germanium solar cells

Structure Configuration Initial Eff (%) Final Eff (%) Reporting laboratory and references

Single-junction uc-SiGe:H 5.3 Tianjin Key Laboratory (2013)

Single-junction uc-SiGe:H 5.5 National Chiao Tung University (2012)

Single-junction a-SiGe:H 11.18 LG (2013)

Single-junction a-SiGe:H 8.26 Beijing Key Laboratory (2013)

Single-junction a-SiGe:H 5.93 ETRI

Single-junction a-SiGe:H 8.59 National Chiao Tung University (2012)

Single-junction a-SiGe:H 8.64 NREL (2009)

Single-junction a-SiGe:H 6.38 ITRI

Double-junction a-Si:H/a-SiGe:H 11.8 Tianjin Key Laboratory (2013)

Double-junction a-Si:H/uc-SiGe:H 11.2 AIST (2012)

Triple-junction a-Si:H/a-SiGe:H/uc-SiGe:H 12.02 Tianjin Key Laboratory (2013)

Triple-junction a-Si:H/a-SiGe:H/a-SiGe:H 9.89 Beijing Key Laboratory (2012)

Triple-junction a-Si:H/a-SiGe:H/a-SiGe:H 14.6 United Solar (1997)

Triple-junction a-Si:H/a-SiGe:H/uc-Si:H 16.1 13.44 LG (2013)

Triple-junction a-Si:H/a-SiGe:H/nc-Si:H 16.3 United Solar (2011)

Triple-junction a-Si:H/a-SiGe:H/nc-Si:H 15.2 LGE (2012)

Triple-junction a-Si:H/a-SiGe:H/nc-Si:H 13.3 United Solar (2005)

Table: 1 Selected results of small area

Problem Statement

Expanding the absorption of the sun light by Silicon-Germanium via reduced band gap.

Research Objectives

1. To design an optimized high efficiency SiGe thin film solar cell structure using SCAPS and ATLAS computer simulation for experimental validation.

2. To fabricate SiGe thin film absorber layers by co-sputtering technique.

3. To investigate the effects of deposition profile (temperature, power and pressure) on the electrical, optical, structural and morphological properties of SiGe absorber layer and subsequently identify the optimum deposition profile.

4. To achieve high photovoltaic conversion efficiency through optimization of SiGe Single-junction solar cell.

Experimental details

Condition of SixGe1-x (0.550.02) films sputtering

Substrate Soda lime glass

Power Si: 50 w / Ge: 25 w

Base pressure 5e-5 Torr

Substrate temperature RT,300,350,400,450,500

Argon flow rate 3 sccm

Thickness 3006% nm

Result & Discussion: FESEM

a-SiGe RT a-SiGe 350 C

a-SiGe 500 C

Result & Discussion: Raman & XRD

Result & Discussion: UV-VIS-IR

1 1.1 1.2 1.3 1.4 1.5 1.60

0.1

0.2

0.3

0.4

0.5

0.6

0.7

a-SiGe

Band-gap: 1.1 eV

Conclusion

• Field Emission Scanning Electron Microscopy (FESEM) also disclosed forming of grains in high temperature.

• crystallinity of the films were improved by increasing temperature above nucleus point of material in the high level of base pressure 5 × 10-5 Torr.

• Optical band gaps of these films derived from Tauc plots (1.1 eV), which were calculated from reflectance/transmittance measurements.

Future Work

1. The gradual improvement of stress type (tensile to compressive) of the SiGe films is subject to further detailed investigation (Temperature and pressure).

2. In order to have investigation on Hall measurement, thicker films have to be prepared.

3. n and p materials should be chosen to make optimum absorber layer.

Research timeline

Feb 2012

I’m here

Feb 2015Feb 2014Feb 2013

3 6 9 12 15 18 21 24 27 30 33 36

To design an optimized high efficiency SiGe thin film solar cell structure using SCAPS and ATLAS computer simulation for experimental validation.

To fabricate SiGe thin film absorber layers by co-sputtering technique.

To investigate the effects of deposition profile (temperature, power and pressure) on the electrical, optical, structural and morphological properties of SiGe absorber layer and subsequently identify the optimum deposition profile.

To achieve high photovoltaic conversion efficiency through optimization of SiGe Single-junction solar cell.

Final thesis

I’m here

Thank You

Q & A