Frontiers of Light Masters School Emerging Photovoltaics
July 2nd, 2018 2-6 July 2018

Monday 2 July, 10:00-11:00
Eli Yablonovitch (University of California Berkeley)
’Photonics of Photovoltaics’

A new scientific principle has produced record-breaking solar cells. The mantra: “A great solar cell has to be a great LED”, has smashed all efficiency records, and is in commercial production. Silicon solar panels are in line to provide about 10% of electricity, but the new super-efficient GaAs technology can eventually provide almost all of the world’s electricity and fuel. This technology is currently being scaled up to the GW level by Alta Devices in China.

Monday 2 July, 16:00-17:00
Blue Lecture Room
Thomas Kirchartz (University of Duisburg-Essen)
’What Makes Metal-Halide Perovskites Special?’

In the lecture, I will start with the basic thermodynamic limits of solar cells (Shockley-Queisser limit) and then discuss how recombination reduces efficiencies and open-circuit voltages below the SQ limit. I discuss recombination mechanisms, the concept of lifetime and surface recombination velocities and discuss how to measure lifetimes at surfaces and interfaces. In my seminar I expand on the topics discussed in the lecture and apply them to metal-halide perovskites to discuss how this material class has special properties that allow high open-circuit voltages despite the relatively simple low temperature solution processing used to fabricate the films.

Tuesday 3 July,12:00-13:00
Blue Lecture Room
Jenny Nelson (Imperial College London)
’Understanding Loss Mechanisms in Organic Solar Cells’

The performance of molecular donor:acceptor solar cells is limited by low photovoltage compared to the optical absorption threshold. We explore the limits to Voc in such systems using a combination of electrical and spectroscopic measurements and a model of non-radiative recombination. We show how chemical structure, the phase behaviour and microstructure of the binary system control performance and address the ultimate limitations placed on solar to electric conversion by the molecular nature of the materials.

Wednesday 4 July, 12:00-13:00
Blue Lecture Room
Maria Antonietta Loi (University of Groningen)
’Controlling Transport Properties in colloidal QDs Solids’

Colloidal quantum dots solids offer the possibility to achieve a major control of their electronic properties by organize them in superlattices and adjusting their stoichiometry, making use of the large surface area of the nanoscale building blocks. In my presentation I will show superlattices with mobility above 20cm2/Vs and I will report about the effective tuning of the nature of the transport properties by acting on the stoichiometry of the QDs. The relation of these findings with QD solar cells efficiency will be highlighted at the end.

Thursday 5 July, 12:00-13:00
Blue Lecture Room
Juan Bisquert (Universitat Jaume I, Castellón)
’Ionic Transport, Defects and Electrooptical Response of Perovskite Solar Cells’

The development of organic-inorganic lead halide perovskites with very large efficiency requires us to understand the operation of the solar cell. This class of semiconductors presents remarkable bulk electronic and optical properties, but the contacts to the device are a key aspect of the operation and show important dynamic interactions. We describe the results of analysis of kinetic phenomena using frequency modulated techniques. With impedance spectroscopy we provide an interpretation of capacitances as a function of frequency both in dark and under light, and we discuss the meaning of resistances and how they are primarily related to the operation of contacts in many cases. The capacitance reveals a very large charge accumulation at the electron contact, which has a great impact in the cell measurements, both in photovoltage decays, recombination, and hysteresis.

Lopez-Varo, P.; Jiménez-Tejada, J. A.; García-Rosell, M.; Ravishankar, S.; Garcia-Belmonte, G.; Bisquert, J.; Almora, O. Device Physics of Hybrid Perovskite Solar cells: Theory and Experiment, Adv. Energy Mater. 2018, 1702772.

Friday 6 July, 12:00-13:00
Blue Lecture Room
Gregory Kozyreff (Université libre de Bruxelles)
Light Trapping Using Whispering Gallery Modes and Chaos’
In this seminar, I’ll present and discuss a new light trapping design based on an array of dielectric cylinders. Experiments show a large improvement of light absorption over a wide spectrum. Theory shows that the underlying trapping mechanism is intermittent ray chaos combined with damped whispering gallery modes.