Enhanced efficiency and current density of solar cells via energy-down-shift having energy-tuning-effect of highly UV-light-harvesting Mn2+-doped quantum dots

Significance Statement

Most researchers have focused on enhancing the power conversion efficiency of crystalline solar cells via innovative methods. They have explored technical methods such as metallization, surface texturing, plasma doping, using anti-reflection coating, designing new structures, etc. Irrespective of these efforts, silicon solar cells still post power conversion efficiency of approximately 25%, therefore leaving a narrow window for improvement.

Generally, silicon solar cells have the ability to absorb photos with energy higher than their band gap, but can only convert the photons to photovoltaic power if the photon energies are closer to the silicon band gap. In simple terms, if the photons energy is higher than the silicon bandgap, the photons will be absorbed but the excess energy, which is the difference between the two, will be lost into the lattice owing to scattering effects. For this reason, conversion efficiencies of silicon solar cells in the UV region is weaker than in the visible region.

The use of energy-down-shift applying quantum dots in silicon solar cells has been proposed recently to absorb the wasted energies in the UV region and emit them in the visible light region. This is in the quest for improved power conversion efficiency. Researchers led by professor Jea-Gun Park at Hanyang University in Republic of Korea implemented the produced Manganese Cd0.5Zn0.5S/ZnS quantum dots on textured mc-p-Si solar cell. The solar cell designed with an antireflective surface, using the benefit of external quantum efficiency as well as the energy tuning effect of the nano quantum dots. This was in a bid to improve power conversion efficiency and short-circuit-current-density. Their work is published in Nano Energy.

The authors doped and spin coated various concentrations of the prepared Manganese: Cd0.5Zn0.5S/ZnS quantum dot solution, onto the surface of the textured Silicon Nitride film of a synthesized mc-p-Si solar cell. They then annealed the quantum dot-coated solar cells to eliminate the remaining solvents from the quantum dot-coated layers. They then obtained the final solar cell devices.

The researchers confirmed that the fabricated Mn2+:Cd0.5Zn0.5S/ZnS quantum dots absorbed UV wavelength light and emitted longer wavelengths visible light via the mechanism of an energy-down-shift and energy tuning effect. The quantum dots were applied to improve absorption and photovoltaic performance of the silicon solar cells. They then investigated the effect of energy-down-shit/energy tuning effect quantum dot layer on the performance. They did this using UV-visible spectroscopy and J-V characterization under solar simulation.

The research team observed that the best-improved performance was reported at 0.3% concentration. This was due to high UV light absorption by the zinc sulfide shell and reduced re-absorption of the visible light with its extensive Stokes shift having an energy tuning effect. Less concentration led to weaker absorption of UV light, while higher concentration increased the direct interaction between adjacent quantum dots. Therefore, higher re-absorption in the visible region.

The best enhancements of power conversion efficiency and short-circuit-current-density were recorded for the solar cells coated with quantum dots layers when the concentration was 3.22 and 4.02%, respectively. The outcomes of their study will have potential in advancing commercial solar cell applications.

Enhanced efficiency and current density of solar cells via energy-down-shift having energy-tuning-effect of highly UV-light-harvesting Mn2+-doped quantum dots- Advances in Engineering

About The Author

Mohammed Jalalah is a Ph.D. candidate in the Advanced Semiconductor Materials/Devices Development Center under the supervision of prof. Jea-Gun Park at Hanyang University. He obtained his M.Sc. in Power Systems Engineering from the University of Manchester in 2008. In 2010, he has joined Najran University as a lecturer in the Department of Electrical Engineering, where he has been involved in the research activities at the Advanced Materials and Nano-Research Centre. His current research activity is focused on the synthesis and characterization of perovskites and quantum dots for solar cells and display.

About The Author

Yun-Hyuk Ko received his M.S. degree from Nano photic materials laboratory for Department of New Materials Engineering, Hannam university, republic of Korea in 2010. He is currently Ph.D. candidate in the Advanced semiconductor materials and devices development center, for Department of Electronics and Computer Engineering, Hanyang University under supervision of Prof. Jea-Gun Park. His research interests focus on the synthesis of quantum dots for photovoltaic and display application.

About The Author

Prof. Farid Harraz is currently a professor at the Advanced Materials and Nano-Research Centre of Najran University, Saudi Arabia. Prof. Harraz has been graduated from Cairo University, Faculty of Science, Chemistry Department in 1991. During 1991-1993, he worked as a researcher assistant at the chemistry department, Faculty of Education, Tanta Univ, Egypt. He then joined Central Metallurgical Research and Development Institute (CMRDI) as a researcher assistant in 1993. He received his MSc degree from Cairo University (Physical Chemistry) in 1997. He has studied his doctor course at the school of Energy Science, Kyoto University, Japan and has been awarded the PhD degree in 2003 (Energy Science). After completion of his PhD, he conducted a post doc fellowship for a couple of years (2003-2005) granted from Japan Society for the Promotion of Science (JSPS) at the Kyoto University. Prof. Harraz was a visiting scholar (short visit) to the Department of Materials Science and Engineering, Univ. of Florida, and Department of Materials Science & Engineering, Univ. of Delaware, USA in 2009 and 2011.

Prof. Harraz’s research career has centered on synthesis, processing and characterization of various nano-structured materials including transition metals, metal oxides and porous semiconductors with various morphologies for energy, sensing and environmental applications. He has also a particular expertise in porous silicon science and technology. Prof. Harraz has outstanding contribution in chemical and electrochemical deposition of metals, metal oxides and conducting polymers, hybrid-organic-inorganic nanostructures, electroless deposition, thin film formation and multilayers.

Prof. Harraz is a member in several national and international scientific societies. He was an invited speaker in several international and national conferences. Prof. Harraz is the author of around 200 articles (75 peer-reviewed papers and 125 proceedings papers and presentations in international conferences and brokerage scientific events and workshops.

Prof. Harraz has been awarded the Federation of Arab Scientific Research Councils first Award for Outstanding Scientific Research in Nanotechnology (2014), The Encouragement State Prize of Advanced Science Technologies in 2009 from Egyptian Government, the award of Environmental Research and Education, Academy of Scientific Research and Technology, Egypt (2012). He has also received the Publication Award from Misr El-Kheir Foundation, Egypt two times on 2010 and 2013 and the award of Prof. Osama El-Khouly in the field of Environmental Research, Academy of Scientific Research and Technology, Egypt (2015).

About The Author

Prof. Mohammad Al-Assiri is a professor of solid state physics at the College of Science and Arts, Najran University, Saudi Arabia and acting as the vice president of postgraduate studies and scientific research. He received his BSc degree from the college of education, King Saud University, Saudi Arabia in 1984 and MSc degree from the college of science, King Saud University, Saudi Arabia in 1989. He has performed his doctor course in Sheffield University, England and has been awarded the PhD degree in 1994. Prof. Al-Assiri served as an assistant professor at King Saud University between the year 1994-1999, where he has acted also as a Vice Dean of Admission and Registration and Student’s Affairs during the year 1995-1997. Then he moved to King Khalid University in 1999 and acted as a Dean of the Student’s affairs (2001-2005). He has been promoted as a full-professor in 2009 and served as a Dean of Faculty of Science at King Khalid University during the year 2010-2011, then moved to Najran University in 2011 where he is currently serving as a professor and vice president of the university.

The research interests of Prof. Al-Assiri focus on structural studies of disordered materials and nano-scale materials for energy and chemical sensor applications. These include semiconducting metal oxides, transition metals and porous materials that have been prepared by various techniques such as Melt spinning technique, Mechanical alloying, Solid-gas reaction and chemical-wet processes.

Prof. Al-Assiri is an active member in several national and international scientific societies and university committees. Prof. Al-Assiri is currently acting as the Chairman of the Scientific Council of the University of Najran since 2011. He is the author of around 100 peer-reviewed scientific papers that can be found in Scopus webpage

About The Author

Prof. Jea-Gun Park, Ph.D. has been a distinguish professor at the Department of Electronics and Computer Engineering, Hanyang University, Seoul, Korea since 1999. He received Ph.D. degree in 1994 at the Department of Material Science and Engineering, North Carolina State University (NCSU), USA., and served as post-doctor in 1995 at the same department. He had been worked at semiconductor division, Samsung Electronics Co. between 1985 and 2002. He is a member of “Korean Academy of Science and Technology” and “National Academy Engineering of Korea”. He has authored 149 patents, 312 papers in the scientific literature, and 645 presentations at international conferences.

Currently, his major research areas are the development of terabit-level CBRAM, perpendicular spin-torque-transfer MRAM, FinFET based on SiGe beyond 10 nm, C-MOS image sensor, cancer-cell detecting bio-sensor, nano-CMP slurry, HVPE GaN substrate, flexible Si & organic solar cell with quantum-dot, and quantum-dots display.

Reference

Mohammed Jalalaha, Yun-Hyuk Ko, Farid A. Harraz, M.S. Al-Assiri, Jea-Gun Park. Enhanced efficiency and current density of solar cells via energy-down-shift having energy-tuning-effect of highly UV-light-harvesting Mn2+-doped quantum dots. Nano Energy, volume 33 (2017), pages 257–265.

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