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DyE SensiTized solar cells wIth eNhanced stabilitY

Final Report Summary - DESTINY (DyE SensiTized solar cells wIth eNhanced stabilitY)

Project Objectives
Our cross-sectoral and multidisciplinary training network Destiny was centred on the development of stable dye-sensitized solar cells, DSC. In Period 1 with the agreement of the supervisory board, external reviewer and project officer the project expanded to include perovskite solar cells, PSCs, that first became widely known in 2012. To address the challenge of improving the lifetime and stability of DSC and PSC whilst maintaining low cost and high performance levels, the following 4 work packages, WP were set up.
WP1 Cell Stability
Aim: To determine the influence of stress conditions on the long-term efficiency and stability of cells and propose materials and device configurations that avoid performance reduction.
WP2 Synthesis
Aim: To find ways of extending device lifetime by providing materials that reduce the main sources of degradation without sacrificing efficiency.
WP3 Modelling
Aim: A unique set of nanoscopic insights into the degradation processes will be provided, which will complement the macrosopic device and impedance models to aid experimental efforts in identifying the key limitations and be compared with spectroscopic data from WP1 and suggest materials that will be employed in WP2.
WP4 Module Stability
Aim To estimate service life of modules and to find ways of extending this life. Similar tests will be carried out as for WP1, but the focus is on modules and based on analysis of the cell accelerated environmental durability tests.

The WP have the following objectives:
(i) clarifying degradation pathways from molecular level to module. (WP1, WP4)
(ii) providing materials design with increased intrinsic stability (WP1, WP2, WP3, WP4)
(iii) stable device architecture by inexpensive and effective encapsulation (WP1)
(iv) defining structural models for interpretation of experimental data (WP3)
(v) defining aging protocols appropriate to DSC and PSC (WP1, WP4)

The main training objectives of Destiny are to provide
(a) multidisciplinary and inter-sectorial approaches so Fellows can cross scientific barriers;
(b) a full portfolio of skills - synthetic chemistry, analytical techniques, device physics, data analysis, materials physics, upscaling - essential for research and development in the renewable energy sector and next generation optoelectronic devices.
(c) an appreciation of market demands, application development and management and communication skills required by business resulting in a superb career development platform allowing Fellows to follow the link from basic science to exploitation.
Fellows have acquired the training and experience that allow them to conduct a successful project in the academic and private sectors and aim at high-level research careers. Dissemination activities, described in a separate section, were integral to the training.

Work performed since the beginning of the project
Research and training went according to the workplan with inclusion of PSC. All Fellows were recruited as anticipated. Minor changes, where additional Fellows were hosted by two partners, were made with the agreement of the Project Officer and the Supervisory Board. Many collaborations took place between the project partners and groups external to the project, often initiated by the Fellows at network meetings, conferences and secondments. Secondments gave the Fellows exposure to different environments (e.g. commercial environments) and techniques.

Local training courses were taken by each Fellow. The network training events were open to external participants. At these events, tutorials were given by academic and industrial partners, that consisted of lectures, practical sessions, exercises and tours of local laboratories. Hard and soft skills e.g. research techniques and skills for business such as intellectual property were covered. Fellows gave talks on their research and held round table discussions.

Destiny achievements
WP1 DSC and PSC degradation were studied at temperatures up to 85ºC specified in International Electrotechnical Commission, IEC, testing protocol 61646. Many perovskite compositions, charge transport layer materials including layered materials, and doping and cell architectures were tested for improved temperature and humidity induced stability. Optical spectroscopy was demonstrated as a valuable probe of layer microstructure and dynamics. The soft matter character of perovskite materials was shown to affect PSC stability. Destiny research addressed breakdown of the perovskite layers due to their volatile constituents. PSCs on metal substrates, allowing them to be used on e.g. warehouse roofs were investigated. A patent was filed: 'Organic Semiconductor Doping Process'.
WP2 For DSC, coadsorbents, solvent free, ionic liquid based redox electrolytes, solid state hole transport layers and novel counter electrode materials were prepared and tested that could improve device stability. For PSC, perovskite and hole transport layers were synthesised that improve cell stability at room temperature and at higher temperatures and under light soaking. Perovskite synthesis was made using environmentally friendly solvents. Incorporation of small amounts of Cs was shown to improve lifetimes from days to a month. Low temperature synthesis of perovskite nanoplatelets that have interesting optoelectronic properties has been demonstrated.
WP3 Electronic structure software packages were used to screen hole transport layer materials by predicting orbital energies and optical spectra. Hysteresis in planar PSC has been shown to come from motion of charged defects. Comparisons between photo-voltage decay transients and electrical models showed the effects of light soaking in perovskites and modelling of impedance spectroscopy data have established a physical explanation for the observations. Commercial software quantified the evolution of the parameters responsible for the degradation of DSCs under thermal stress.
WP4 Destiny has demonstrated scalable fabrication methods such as vapour-assisted solution processing at low pressures in air, encapsulation methods and fabrication methods that are reproducible and improve lateral uniformity. A commercial sealant was shown to perform well. Destiny research has laid a platform for an effort that can address the challenges for modules that differ from those at the small cell level, such as encapsulation of interconnections and contacts, non-uniformity of layer stacks and cells, reverse bias stresses.

Socio-economic impact and the wider societal implications of the project
Large-scale application of renewable energy will have a significant benefit for global and regional climate. Photovoltaics, PV, has huge potential for secure and sustainable energy. Perovskites are a class of materials whose distinctive structure has been shown to give cells of high power conversion efficiencies that rival and even outperform silicon cells. These materials are also predicted to play a role in next-generation electric vehicle batteries, sensors, lasers. Dye-sensitized and perovskite cell technologies are potentially low cost and are simple to manufacture, requiring a much lower energy input than other PV technologies. Destiny has provided highly trained individuals in these technologies and has found ways of extending lifetimes during operation, thus helping overcome a major barrier to exploitation.