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 SHAHAHMADI P64797 Solar Energy Research Institute (SERI) Universiti Kebangsaan Malaysia Supervisor: Prof. Dr. Nowshad Amin Prof 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 cells To 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 StructureConfigurationInitial Eff (%)Final Eff (%)Reporting laboratory and references Single-junctionuc-SiGe:H5.3Tianjin Key Laboratory (2013) Single-junctionuc-SiGe:H5.5National Chiao Tung University (2012) Single-junctiona-SiGe:H11.18LG (2013) Single-junctiona-SiGe:H8.26Beijing Key Laboratory (2013) Single-junctiona-SiGe:H5.93ETRI Single-junctiona-SiGe:H8.59National Chiao Tung University (2012) Single-junctiona-SiGe:H8.64NREL (2009) Single-junctiona-SiGe:H6.38ITRI Double-junctiona-Si:H/a-SiGe:H11.8Tianjin Key Laboratory (2013) Double-junctiona-Si:H/uc-SiGe:H11.2AIST (2012) Triple-junctiona-Si:H/a-SiGe:H/uc-SiGe:H12.02Tianjin Key Laboratory (2013) Triple-junctiona-Si:H/a-SiGe:H/a-SiGe:H9.89Beijing Key Laboratory (2012) Triple-junctiona-Si:H/a-SiGe:H/a-SiGe:H14.6United Solar (1997) Triple-junctiona-Si:H/a-SiGe:H/uc-Si:H LG (2013) Triple-junctiona-Si:H/a-SiGe:H/nc-Si:H16.3United Solar (2011) Triple-junctiona-Si:H/a-SiGe:H/nc-Si:H15.2LGE (2012) Triple-junctiona-Si:H/a-SiGe:H/nc-Si:H13.3United 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 SubstrateSoda lime glass PowerSi: 50 w / Ge: 25 w Base pressure5e-5 Torr Substrate temperatureRT,300,350,400,450,500 Argon flow rate3 sccm Thickness

Result & Discussion: FESEM a-SiGe RT a-SiGe 350 C a-SiGe 500 C

Result & Discussion: Raman & XRD

Result & Discussion: UV-VIS-IR 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 × 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 2014 Feb 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