Dilute Nitride Type II Quantum Dot Materials for Solar Cells based on GaAs - Collaborative Research in Energy with South Africa

Lead Research Organisation: Lancaster University
Department Name: Physics


The development of efficient, affordable solar cells for clean energy production is a major global challenge and in this proposal we are seeking to achieve a breakthrough in the fabrication of novel quantum dot materials capable of substantially improving the performance of III-V solar cells based on GaAs. We propose a close collaborative project with Nelson Mandela Metropolitan University in South Africa, who have complementary expertise in photovoltaic cells, to develop and characterize hitherto unexplored GaSbN/GaNAs type-II quantum dot materials. These strain-compensated, dilute-nitride quantum dots will be implemented within the active region of prototype GaAs based solar cells to significantly extend the spectral response and improve the efficiency. This would lead to a new generation of solar cells for clean electricity generation. Feedback from device studies will provide valuable insight into the photovoltaic properties of these unique nanostructures, further aiding material optimization. The quantum dot materials that we shall develop here could either be used to increase efficiency in single junction cells, or could be incorporated into existing multi-junction cells to replace expensive Ge substrates, reduce cost and significantly increase performance. There are clear opportunities for uptake of the technology both within South Africa and the UK.


10 25 50
Description In this work we have fabricated GaAs solar cells containing stacked layers of novel nanostructures of GaSb quantum rings (QR) with extended photo-response and much higher performance. Specifically we have;
1) Achieved an enhanced short-circuit of 27.9 mA/cm2 under 1 sun illumination for a 10 layer stack of GaSb QR inserted within the active region of a GaAs solar cell, which is 6 % higher compared to a GaAs control cell. The corresponding open-circuit voltage of 0.6 V is close to the theoretical maximum expected from such a structure.
2) Demonstrated the first Quantum Ring solar cell containing 10 layers of stacked GaSb/GaAs rings with excellent structural quality and no threading dislocations. This was achieved through the QR formation during capping which reduces the strain energy avoiding the use of GaAsN strain compensation layers.
3) Realized a breakthrough in the MBE growth of GaSb QRs whereby exact control of the As flux enabled the QRs to be capped at high growth temperatures, which increased their structural and optical quality.
Exploitation Route Quantum dot (QD) nanostructures are attracting great interest for use in solar cells as a means of absorbing long wavelength photons to extend the photoresponse into the infrared to increase the short-circuit current. Previous studies have focused on InAs/GaAs QDs where an extension of the long wavelength photoresponse to around 1100 nm has been realized with typical short-circuit enhancements of 3.5% for 10 stacks of dots. An attractive alternative system is type II GaSb/GaAs QDs, such that holes are localized within the GaSb QDs, but there is no electron confinement. Compared to InAs QDs this produces a red-shift of the photoresponse and captures more of the infrared solar spectrum, increasing the short-circuit current.
Sectors Education,Energy

Description Our findings are being used to inform and develop improved multi-junction III-V solar cells. Type II GaSb quantum dots are being used in intermediate band solar cells to increase efficiency.
First Year Of Impact 2013
Sector Education,Energy
Impact Types Societal

Description Marie Curie
Amount € 4,000,000 (EUR)
Funding ID PITN-GA-2010-264687 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 01/2011 
End 12/2015
Description Marie-Curie H2020 ITN
Amount € 3,974,560 (EUR)
Funding ID 641899 
Organisation EU-T0 
Sector Public
Country European Union (EU)
Start 01/2015 
End 12/2018
Title MBE growth reactor 
Description A new Veeco GenXplore MBE growth reactor with 10 ports for growth of III-V antimonide and dilute nitride nanostructures and devices was secured from European funding partly as a result of our successful research work on this project. 
Type Of Material Improvements to research infrastructure 
Year Produced 2014 
Provided To Others? Yes  
Impact The new reactor is to be installed during the next 2 months. Samples will be grown and provided to collaborators and other researchers. in the near future. 
Title dilute nitride epitaxial samples for research 
Description we have developed the MBE growth of low bandgap dilute nitride materials - InAsN, InAsSbN 
Type Of Material Improvements to research infrastructure 
Year Produced 2013 
Provided To Others? Yes  
Impact Samples have been provided to a number of groups for further studies including high pressure, photoreflectance and Hydrogenation measurements e.g. at Surrey, Wroclaw, Taiwan, Rome resulting in (joint) publications. 
Description NMMU S Africa 
Organisation Nelson Mandela Metropolitan University
Country South Africa 
Sector Academic/University 
PI Contribution Sample growth and processing, data analysis and preparation of joint publications
Collaborator Contribution staff time at NMMU for TEM and spectroscopic analysis of solar cell materials and devices, preparation of publications and analysis of results
Impact We have produced several joint publications in peer reviewed scientific journals as well as international conference outputs
Start Year 2008
Description Open days 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Our research was showcased to sixth form students and also members of the general public on visit days and open lab days by our postdocs and research students throughout the year. Activities involved short explanatory talks and lab tours including question and answers.

UCAS applications to Lancaster Physics have increased partly as a result of our outreach programme.
Year(s) Of Engagement Activity Pre-2006,2006,2007,2008,2009,2010,2011,2012,2013,2014