Challenges and opportunities in printed photovoltaics
Professor James Durrant FRS, Imperial College London, UK
Professor Durrant will address some of the key challenges and opportunities for organic and perovskite based solar cells. He will start by discussing the motivations for such printed photovoltaic technologies, and the market opportunities for these technologies. He will discuss some of the recent advances in the efficiencies and stabilities of these devices, including in particular the development of non-fullerene acceptors for organic solar cells, and stability limitations for both organic and perovskite solar cells.
Designing dopants for higher performance transparent conducting oxides
Dr David Scanlon, University College London, UK
The combination of electrical conductivity and optical transparency in a single material gives transparent conducting oxides (TCOs) an important role in modern optoelectronic applications such as in solar cells, flat panel displays, and smart coatings. The most commercially successful TCO so far is tin doped indium oxide (Indium Tin Oxide – ITO), which has become the industrial standard TCO for many optoelectronics applications: the ITO market share was 93% in 2013. Its widespread use stems from the fact that lower resistivities have been achieved in ITO than in any other TCO; resistivities in ITO have reached as low as 7.2 × 10-5Ω cm, while retaining >90% visible transparency. In recent years, the demand for ITO has increased considerably, mainly due to the continuing replacement of cathode ray tube technology with flat screen displays. However, indium is quite a rare metal, having an abundance in the Earth’s crust of only 160 ppb by weight, compared with abundances for Zn and Sn of 79000 ppb and 2200 ppb respectively, and is often found in unstable geopolitical areas. The overwhelming demand for ITO has led to large fluctuations in the cost of indium over the past decade. There has thus been a drive in recent years to develop reduced-indium and indium-free materials which can replace ITO as the dominant industrial TCO. In this talk Dr Scanlon will outline a new doping mechanism, and a new TCO which should usurp ITO as the industry standard.
Tandem dye-sensitised solar cells for energy conversion and storage
Dr Libby Gibson, Newcastle University, UK
One way of improving the efficiency of dye-sensitised solar cells is to use two photoelectrodes in a tandem device, one harvesting the high energy photons, and the other harvesting the low energy photons . This enables the photovoltage to be increased, whilst maximizing light harvesting across the solar spectrum. Despite their promise, a tandem cell with a higher efficiency than the state-of-the-art ‘Grätzel’ cell has not yet been achieved. This is because the performances of photocathodes are significantly lower than TiO2-based anodes, and the p-type concept has been largely unexplored since the first device was prepared in 1999 . The small potential difference between the valence band of the NiO, p-type semiconductor, and the redox potential of the electrolyte and the faster charge-recombination reactions compared to the TiO2 system limits the efficiency. In recent years the researchers have made progress by developing new photosensitisers . In parallel the researchers have investigated the charge-transfer processes to determine the mechanism and limitations to efficiency . This has increased our understanding of the redox processes at the dye/electrolyte and NiO/electrolyte interfaces . The fundamental limitation of these devices arises from the NiO material itself and the researchers have re-focussed our efforts on finding a replacement transparent p-type semiconductor. The group’s strategy and recent results will be presented. Recent work to expand the applications to photoelectrochemical water splitting for energy storage will be described, briefly .
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CJ Wood, GH Summers, EA Gibson. Chem Commun 2015, 51, 3915 – 3918.
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EA Gibson, Chem Soc Rev, 2017, 46, 6194 – 6209. N Põldme, L O’Reilly, I Fletcher, I Sazanovich, M Towrie, C Long, JG Vos, MT Pryce, EA Gibson Chem Sci In press.
Non-conventional solar cells: need for new techniques for new devices
Professor Emilio Palomares, ICIQ Tarragona, Spain
During his lecture Professor Palomares will present his group latest results on the characterisation of different type of solar cells from DSSC and OPV to MAPI using advanced photo-induced time resolved techniques [1-4]. Using PICE (Photo-induced charge extraction), PIT-PV (Photo-induced Transient PhotoVoltage) and other techniques, the researchers have been able to distinguish between capacitive electronic charge, and a larger amount of charge due to the intrinsic properties of the perovskite material. Moreover, the results allow us to compare different materials, used as hole transport materials (HTM), and the relationship between their HOMO and LUMO energy levels, the solar cell efficiency and the charge losses due to interfacial charge recombination processes occurring at the device under illumination. These techniques and the measurements carried out are key to understand the device function and improve further the efficiency and stability on perovskite MAPI based solar cells.
1. 1) JM Marin-Beloqui; L Lanzetta; E Palomares; Decreasing Charge Losses in Perovskite Solar Cells Through mp-TiO2/MAPI Interface Engineering. Chem Mater 2016, 28, 207-213.
2) BC O'Regan; PRF Barnes; X Li; C Law; E Palomares; JM Marin-Beloqui; Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO2: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J-V Hysteresis. J Am Chem Soc 2015, 137, 5087-5099.
3. 3) A Matas Adams; JM Marin-Beloqui; G Stoica; E Palomares; The influence of the mesoporous TiO2 scaffold on the performance of methyl ammonium lead iodide (MAPI) perovskite solar cells: charge injection, charge recombination and solar cell efficiency relationship. J Mater Chem A 2015, 3, 22154-22161.
4. 4) L Cabau; I Garcia-Benito; A Molina-Ontoria; NF Montcada; N Martin; A Vidal-Ferran; E Palomares; Diarylamino-substituted tetraarylethene (TAE) as an efficient and robust hole transport material for 11% methyl ammonium lead iodide perovskite solar cells. Chem Commun 2015, 51, 13980-13982.
Professor Saiful Islam, University of Bath, UK
Professor Jenny Nelson FRS, Imperial College London, UK