Speaker: Prof.Giulia Grancini, Univeristy of Pavia
Time：Friday,9:30-10:30 a.m.,18th October
Place：A718
Sponsor：Prof. MA Changqi

Abstact：
Solar energy can lead a “paradigm shift” in the energy sector with a new low-cost, efficient, and stable technology. Nowadays, three-dimensional (3D) methylammonium lead iodide perovskite solar cells are undoubtedly leading the photovoltaic scene with their power conversion efficiency (PCE) >23%, holding the promise to be the near future solution to harness solar energy [1]. Tuning the material composition, i.e. by cations and anions substitution, and functionalization of the device interfaces have been the successful routes for a real breakthrough in the device performances [2]. However, poor device stability and still lack of knowledge on device physics substantially hamper their take-off. Here, I will show a new concept by using a different class of perovskites, arranging into a two-dimensional (2D) structure, i.e. resembling natural quantum wells. 2D perovskites have demonstrated high stability, far above their 3D counterparts [3]. However, their narrow band gap limits their light-harvesting ability, compromising their photovoltaic action. Combining 2D and 3D into a new hybrid 2D/3D heterostructure will be here presented as a new way to boost device efficiency and stability, together. The 2D/3D composite self-assembles into an exceptional gradually organized interface with tunable structure and physics. To exploit new synergistic function, interface physics, which ultimately dictate the device performances, is explored, with a special focus on energy and charge transfer dynamics, as well as charge recombination and trapping processes happening over a time scale from fs to ms. As shown in Fig.1, when 2D perovskite is used on top of the 3D, charge transfer happens, while electron hole recombination at the perovskite/hole transporter interface is prevented. This results in improved device efficiency. In concomitance, the stable 2D perovskite is used as a sheath to physically protect the 3D underneath, with the aim to enhance the device stability. The joint effect leads to PCE=20% which is kept stable for 1000 h [3,4]. Incorporating the hybrid interfaces into working solar cells is here demonstrated as an interesting route to advance in the solar cell technology bringing a new fundamental understanding of the interface physics at multi-dimensional perovskite junction. The knowledge derived is essential for a deeper understanding of the material properties and for guiding a rational device design, even beyond photovoltaics. 
Biography:
Giulia Grancini is Associate Professor at Physical Chemistry Section at Univeristy of Pavia, leading the PVsquared2 group. Giulia’s work focuses on the current scientific challenge of exploring the fundamental photophysical processes underlying the operation of advanced optoelectronic devices, with a special attention to new generation photovoltaics (PVs). She is principal investigator of the ERCStG Project HYNANO, aiming at the development of advanced hybrid perovskites materials and innovative functional interfaces for efficient, stable, enviromentally friendly and cheap PVs.