Elena Cassella

Cohort 5


I am an MChem Chemistry graduate from the University of Sheffield. My Master's project investigated the strong coupling interaction between excitons in light-harvesting molecules and plasmonically-active gold surfaces. Inspired to pursue a PhD in photovoltaics, i've signed up for another four years in the Steel City - albeit across the road in the Physics department!


Spray-coating perovskite PV devices over curved substrates

Conventional PV cells based on the ubiquitous semiconductor crystalline-silicon most often come in the form of flat, rigid and relatively heavy panels. Despite the fact that PV devices can be manufactured on flexible substrates, methods to integrate PV devices onto the surface of non-planar (3-dimensional) objects are not well developed. Whilst the collection of sunlight for power generation in solar-farms or roof-mounted systems is well served by conventional two-dimensional devices, there are a range of applications in which it is desirable to cover the surface of 3D object with PV devices. These include building cladding, and various consumer products embedded with software, sensors and internet connectivity that collect and exchange data. A key objective of this experimental research project is to develop a manufacturing technology that will allow efficient PV devices to be integrated in an unobtrusive fashion over the surface of 3D objects. Central to this project is the ability to spray-cast functional semiconductors [1] over non-planar surfaces. The materials of interest to this proposal are solution-processable organometal-halide perovskites. A key task for the student will be to develop a toolbox of materials and spray-coating process techniques that can be applied over curved surfaces such as moulded PMMA and polystyrene substrates. The key science challenge to be addressed is to open a sufficiently wide process-window permitting a surface having some degree of surface-roughness to be used as the substrate for a perovskite solar cell. This will involve metrology of various substrates to characterize roughness, and the possible use of spray-coated planarization layers [2] to control roughness. Once a suitable substrate has been developed, the student will then explore the sputter deposition of various TCO coatings onto the substrates onto which they will then spray-coat charge transporting and perovskite layers. Here, the student will follow strategies previously used to fabricate perovskite solar cells onto flexible substrates (making them compatible with moulded plastic substrates), requiring the use of low temperature processes. For example, one target structure that will be explored are n-i-p structures such as PEI:PCBM/MAPI/PTAA/MoOx/Ag onto TCO-coated substrates [3]. Typical devices will have an active area of up to 1 cm2. The student will utilize semi-transparent (dielectric / metal /dielectric) top electrodes deposited by thermal evaporation [4] allowing light to be harvested through the device top contact even if the substrate is opaque. We also plan to explore the use of new metal materials as high stability contacts. Here one system of significant interest is that of copper, which has shown to result in devices having enhanced performance and stability [5]. Once a reliable process for to fabricate devices on planar substrates has been established, the student will adapt the coating techniques to fabricated devices over curved substrates. [1] ‘Spray-cast multilayer perovskite solar cells with an active-area of 1.5 cm2’ J.E. Bishop et al, Scientific Reports, 7 (2017) 7962 [2] ‘Towards 3D-printed organic electronics: Planarization and spray-deposition of functional layers onto 3D-printed objects’ A. Falco et al, Organic Electronics 39 (2016) 340-347 [3] ‘A Printable Organic Electron Transport Layer for Low-Temperature-Processed, Hysteresis-Free, and Stable Planar Perovskite Solar Cells’ J. Lee et al, Adv. Energy Mater (2017) 1700226 [4] ‘Ultra-thin high efficiency semitransparent perovskite solar cells’ E. Della Gaspera, Nano Energy 13 (2015) 249–257. [5] ‘Efficient Flexible Solar Cell based on Composition-Tailored Hybrid Perovskite’ C. Bi et al, Advanced Materials, 29 (2017) 1605900