(Invited) Morphological Control and Kinetics Characterization for Perovskite Solar Cells

The development of all solid-state thin-film solar cells has reached a new milestone when the devices made of organometallic lead halide perovskite materials were reported with power conversion efficiency (PCE) exceeding 19 %. The key issue to make a device with a great photovoltaic performance for perovskite solar cells is to control the film morphology of perovskite under different experimental conditions. In this lecture, I will demonstrate how the film morphology of perovskite can be controlled via varied synthetic approaches. Typical n-type device has a structural configuration FTO/TiOx/TiO₂/CH₃NH₃PbI₃/Spiro-OMeTAD/Au whereas that of a p-type device is configured as ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Al. For n-type devices, varied mesoporous TiO₂ nanostructures were applied to show the morphological effect of the scaffold on the device performance with a mesoscopic heterojuction; for p-type devices, varied additives were applied to control the formation morphology of the perovskite nanocrystals with a planar heterojunction. Photo-induced absorption (PIA) spectra and nanosecond transient absorption (ns-TAS) kinetics were also performed to understand the electron-hole recombination rates responsible for the corresponding device performances. Measurements of power dependence on emission intensities vs excitation power densities were also performed and an Auger-type energy transfer model was utilized to rationalize the observed relaxation dynamics.