SOPHY wants to probe optoelectronic processes at buried interfaces in devices, at operating conditions. This is a target which has been long pursued in many fields of nanotechnology for the study of multi-junctions devices, which includes solar cells, light-emitting diodes (LEDs), electro-chemical and photo-catalytic devices. However, so far, direct probe has not been fully achieved. Information has been often built on indirect feedback1 obtained from studies employing independent techniques and from simplified model systems or on experimental data collected without the appropriate temporal/spatial resolution. Unfortunately, given the complexity of interfacial processes, such approaches are not immune from misinterpretation.
Semiconducting metal halide perovskites, and devices based on them, is the primary technology under investigation, given its potential to represent the merging point between the efficient inorganic and the chameleonic organic electronics. The presence of various types chemical interactions in such complex ionic solids gives them a characteristic “soft” fluctuating structure, prone to a wide set of defects which span from lattice distortions to the presence of mobile ions. These are sensitive to the devicoperating conditions, thus, the control of structure-properties relationship, especially at interfaces, becomes elusive, and the prediction of device operation, necessary to engineer reliable systemsj
Perovskite based photovoltaic (PV) devices have recently made spectacular progress in terms of device efficiency, however, the reported values still belong to devices electrically unstable as noted in the NRL efficiency chart5. Promising proofs of concept have been realized for LEDs and optically pumped lasers6, with good perspective for electrically pumped ones. On the other hand, field effect transistors are not taking off yet, and the reason behind this is still unknown. Upon thin film polarization and illumination, slow transients and hysteretic effects have been reported with a variety of dynamics which differ in magnitude and time scale, depending both the material processing and on the specific device architecture, indicating that contact interfaces have a considerable effect This implies a lack of predictive design of the device, pivotal in the development of a reliable technology. There is no direct experimental method that measures the band diagram, and carrier and electric field distributions and evolution in a completed diode. Thus, the study of buried interfaces and the electrostatic of an heterojunction based diode, which will eventually determine the device performances, is a difficult task. For perovskite based devices it is even harder.
SOPHY overall objective is the development and exploitation of an experimental approach which will put together the advantages of optical spectroscopy and electronic spectroscopy and microscopy and will challenge their limitations when taken individually. Time-resolved (visible) pump- (UV)push photoelectron (Tr-PPE) spectroscopy set up will be coupled to a photoelectron microscope (PEEM). Here, this system will be developed to reach, within the same experiment, both time and space resolution . It will map in space electronic structures and the related excitations and how they evolve in time over a large timescale (from femtoseconds to microseconds), in order to follow a wide set of cascade phenomena. Such approach, implemented for the first time on diodes’ cross-sections, will provide the possibility of studying the device at different operation conditions, the key to monitor the “real life” transformations related to the defect physical chemistry of metal halide perovskites
The achievemnt of such target will allow the educated design of perovskite based optoelectronic design, boosting the development of a new technological platform for optoelectronics
