Deciphering Grain Boundaries in Ideal-Bandgap Inorganic Perovskite Semiconductors

The introduction of halide perovskite (HP) semiconductors have led to the emergence of a disruptive photovoltaic technology. However, the progress of perovskite-based solar cells (PSCs) is limited by two intrinsic issues of state-of-the-art HPs: non-ideal bandgaps (over 1.45 eV) and inclusion of volatile organic-cations. In this context, this project probes the critical fundamental materials science centered at grain boundaries (GBs) in these inorganic, mixed Pb-Sn HPs with ideal bandgaps (sub-1.4 eV), which will be of vital importance for simultaneously addressing the above two issues and realizing stable PSCs with the potential for approaching the theoretical efficiency limit.

It is well-known that GB is the most prominent microstructural feature in HPs, but fundamental understandings on the structures and functions of HP GBs are still in their infancy. The reported GB studies have primarily focused on hybrid organic-inorganic HPs. It is claimed in general that GBs serve as non-radiative recombination centers and ionic/molecular transport channels, influencing the carrier transport and chemical stability of HPs, respectively. But the quantified HP GB characteristics such as local defect chemistry, geometry and degree of order and their influence on GB effects have been less discussed. Furthermore, the previous studies rarely involve the discussion on Sn-related defects at HP GBs which largely affect the properties of ideal-bandgap HPs.

Therefore, this proposed research aims to decipher the emerging GB phenomena in ideal-bandgap, inorganic, mixed Pb-Sn HPs. The core approach involves: (i) elucidating the GB structure-property relationship at the nanoscale using a set of advanced correlated characterizations involving variable transmission electron microscopy approaches; (ii) exploring advanced GB tailoring strategies based on novel chemical additives including a novel series of Sn(II) halide complex; (iii) improving the device efficiency and stability based on tailored GBs. The successful completion of this project is expected to be built upon the PI’s well-established expertise in related areas in the fast-moving perovskite field.

The outcome of this project will have far-reaching impacts not only for developing high-efficiency stable PSCs that opens the door to the Shockley–Queisser limit, but also for unravelling new physical sciences related to the board materials family of perovskites regarding their microstructures, defects, and properties, which have significant implication to numerous functional devices beyond PVs, such as near- infrared light-emitting and photodetection devices.