Improving the solar cells efficiency of metal Sulfide thin-film nanostructure via first principle calculations

Transcription

1 Improving the solar cells efficiency of metal Sulfide thin-film nanostructure via first principle calculations Alwaleed Adllan Abusin, PhD Elzina Bala Africa City of Technology

2 Agenda INTRODUCTION TO HIGH-PERFORMANCE COMPUTING SULFIDE THIN-FILM NANOSTRUCTURE CALCULATION METHODS OPTICAL PROPERTIES

3 What is Scientific Computing? Short Version To use high-performance computing (HPC) facilities to solve real scientific problems. Long Version, from Wikipedia.com Scientific computing (or computational science) is the field of study concerned with constructing mathematical models and numerical solution techniques and using computers to analyze and solve scientific and engineering problems. In practical use, it is typically the application of computer simulation and other forms of computation to problems in various scientific disciplines.

4 What is Scientific Computing? Engineering Sciences Theory/Model Layer Applied Mathematics Scientific Computing Computer Science Algorithm Layer Hardware/Software Natural Sciences Application Layer From scientific discipline viewpoint From operational viewpoint Parallel Computing High- Performance Computing Scientific Computing From Computing Perspective

5 What is HPC? Computing resources which provide more than an order of magnitude more computing power than current top-end workstations or desktops generic, widely accepted. HPC ingredients: large capability computers (fast CPUs) massive memory enormous (fast & large) data storage highest capacity communication networks (Myrinet, 10 GigE, InfiniBand, etc.) specifically parallelized codes (MPI, OpenMP) visualization

6 Measure of Performance 1 CPU, Units in MFLOPS (x10 6 ) Machine/CPU Type LINPACK Performance Peak Performanc e Intel Pentium 4 (2.53 GHz) NEC SX-6/1 (1proc. 2.0 ns) HP rx5670 Itanium2 (1GHz) IBM eserver pseries 690 (1300 MHz) Cray SV1ex-1-32(500MHz) Compaq ES45 (1000 MHz) AMD Athlon MP1800+(1530MHz) Intel Pentium III (933 MHz) SGI Origin 2000 (300 MHz) Intel Pentium II Xeon (450 MHz) Sun UltraSPARC (167MHz) Mega FLOPS (x10 6 ) Giga FLOPS (x10 9 ) Tera FLOPS (x10 12 ) Peta FLOPS (x10 15 ) Exa FLOPS (x10 18 ) Zetta FLOPS (x10 21 ) Yotta FLOPS (x10 24 ) Reference:

7 Current Solar Cell efficiency SHOCKLEY-QUIESSER LIMIT : PREDICT A HEORETICAL POWER CONVERSION EFFICIENCY (PCE) LIMIT FOR A CZTS SOLAR CELL OF 28% CURRENTLY THE HIGHEST PERFORMING DEVICES ARE ACHIEVING EFFICIENCIES FAR BELOW THIS LIMIT WITH THE PCE OF RECORD DEVICES AT AROUND 22% LOW OPEN CIRCUIT VOLTAGE (V OC ) RELATIVE TO THE BAND GAP HAS BEEN RECOGNIZED AS A KEY BOTTLENECK FOR THE PERFORMANCE OF CZTS SOLAR CELLS.

8 Candidate Matterial we identified three sulfosalt minerals: enargite (Cu3AsS4), stephanite (Ag5SbS4), bournonite (CuPbSbS3), All Materials that contain two or more metals, semi-metals such as antimony and arsenic, and sulfur This work also provides an overview of thin lm deposition methods that have been developed for synthesizing sulfosalt layers and discusses a 1% efficient Sn-Sb-S sulfosalt thin lm solar cell constructed by the authors.

9 Candidate Matterial The unit cell (as shown next slide) has an orthorhombic crystal structure with space group Pmn21 and tetrahedral coordination for all atoms

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13 Computational Methods The electronic structure of the three candidate materials was calculated using the VASP electronic structure code, which is an implementation of density functional theory (DFT) based on numeric atom-centered orbital basis sets with a linearscaling approach to hybrid functionals. We use the short-range screened hybrid exchange correlation HSE06 functional and spin orbit coupling (SOC) is included. Hybrid DFT functionals have been found to correct for the underestimation of the optical band gap inherent in the generalized gradient and local density approximation

14 Results An effective PV material must absorb light and transport charge. In addition to the band gap and carrier effective masses, we consider the dielectric function, and the associated optical absorption spectra We finish with an assessment of spontaneous electric polarisation to determine the strength of the polarity in the materials and the effect on the electronic band structure.

15 The real component of the electron wavefunction of the highest occupied state, showing sulfur p-orbitals and copper d-orbital in enargite and bournonite and silver d-orbitals in stephanite

16 HSE06 + SOC partial electronic density of states (pdos) of enargite (Cu3AsS4), where the top of the valence band has been set to 0 ev.

17 Three independent components of the calculated optical dielectric tensor, E(u), as a function of incident photon energy, for enargite (Cu3AsS4).

18 optical absorption coefficient for three sulfosalt materials enargite (Cu3AsS4), stephanite (Ag5SbS4) and bournonite (CuPbSbS3) plotted in comparison to the same parameter for other important photovoltaic materials over the onset energy range (1 3 ev).

19 Conclusion Our study has shown that the three minerals merit deeper investigation. In addition to further experimental work on synthesis, characterisation and optimisation, the extension of theoretical investigations to include analysis of the defect tolerance of the bulk (beyond the speculation made in this study based on the bonding character of the VBM), and identifying compatible interfaces for high-efficiency devices could help to accelerate the development of these new technologies.