Passivation engineering via silica-encapsulated quantum dots for highly sensitive photodetection

Organometal halide perovskites are promising semiconducting materials for photodetectors because of their favorable optoelectrical properties. Although nanoscale perovskite materials such as quantum dots (QDs) show novel behavior, they have intrinsic stability issues. In this study, an effectively silane barrier-capped quantum dot (QD@APDEMS) is thinly applied onto a bulk perovskite photosensitive layer for use in photodetectors. QD@APDEMS is synthesized with a silane ligand with hydrophobic CH3-terminal groups, resulting in excellent dispersibility and durability to enable effective coating. The introduction of the QD@APDEMS layer results in the formation of a low-defect perovskite film with enlarged grains. This is attributed to the grain boundary interconnection effect via interaction between the functional groups of QD@APDEMS and uncoordinated Pb2+ in grain boundaries. By passivating the grain boundaries, where various trap sites are distributed, hole charge-carrier injection and shunt leakage can be suppressed. Also, from the energy point of view, the deep highest occupied molecular orbital (HOMO) level of QD@APDEMS can work as a hole charge injection barrier. Improved charge dynamics (generation, transfer, and recombination properties) and reduced trap density of QD@APDEMS are demonstrated. When this perovskite film is used in a photodetector, the device performance (especially the detectivity) stands out among existing perovskites evaluated for energy sensing device applications.