ABSTRACT
Hybrid organic-inorganic perovskites are one of the promising candidates for the next-generation semiconductors due to their superlative optoelectronic properties. However, one of the limiting factors for potential applications is their chemical and structural instability in different environments. Herein, the stability of (FAPbI3 )0.85 (MAPbBr3 )0.15 perovskite solar cell is explored in different atmospheres using impedance spectroscopy. An equivalent circuit model and distribution of relaxation times (DRTs) are used to effectively analyze impedance spectra. DRT is further analyzed via machine learning workflow based on the non-negative matrix factorization of reconstructed relaxation time spectra. This exploration provides the interplay of charge transport dynamics and recombination processes under environment stimuli and illumination. The results reveal that in the dark, oxygen atmosphere induces an increased hole concentration with less ionic character while ionic motion is dominant under ambient air. Under 1 Sun illumination, the environment-dependent impedance responses show a more striking effect compared with dark conditions. In this case, the increased transport resistance observed under oxygen atmosphere in equivalent circuit analysis arises due to interruption of photogenerated hole carriers. The results not only shed light on elucidating transport mechanisms of perovskite solar cells in different environments but also offer an effective interpretation of impedance responses.
ABSTRACT
Organic electron-transporting materials (ETMs) with low-temperature solution processability and high electron-transfer/transport characteristics have received significant attention for their use in high-performance perovskite solar cells (PSCs). In contrast to widely investigated fullerene-based organic ETMs for PSCs, only a few types of non-fullerene-based ETMs have been developed. In this Concept article, a representative design concept for non-fullerene ETMs is described for use in normal (n-i-p) and inverted (p-i-n) type PSCs. On the basis of a discussion on ETM requirements for PSCs, recently developed non-fullerene polymeric and small-molecule-based ETMs for PSCs are highlighted, alongside various other approaches for enhancing PSC device performance, such as using additional dopants and introducing amine terminal groups in the ETMs and ETM-based interlayers. This Concept provides a basic design concept for non-fullerene-based ETMs in PSCs.
ABSTRACT
Organic-inorganic lead halide perovskite is emerging as a potential emissive material for light emitting devices, such as, light emitting diodes (LEDs) and lasers, which has emphasized the necessity of understanding its fundamental opto-physical properties. In this work, the temperature-dependent photoluminescence of CH3NH3PbBr3 perovskite quantum dots (QDs), polycrystalline thin film (TF), and single crystal (SC) has been studied. The optophysical properties, such as exciton-phonon scattering, exciton binding energy, and exciton decay dynamics, were investigated. The exciton-phonon scattering of perovskite is investigated, which is responsible for both PL line width broadening and nonradiative decay of excitons. The exciton binding energy of QDs, TF, and SC were estimated to be 388.2, 124.3, and 40.6 meV, respectively. The observed main exciton decay pathway for QDs is the phonon assisted thermal escape, while that for TF and SC was the thermal dissociation due to low exciton binding energy.
