Grain boundaries in lead halide perovskite films lead to increased recombination losses and decreased device stability under illumination due to defect‐mediated ion migration. The effect of a conjugated polymer additive, poly(bithiophene imide) (PBTI), is investigated in the antisolvent treatment step in the perovskite film deposition by comprehensive characterization of perovskite film properties and the performance of inverted planar perovskite solar cells (PSCs). PBTI is found to be incorporated within grain boundaries, which results in an improvement in perovskite film crystallinity and reduced defects. The successful defect passivation by PBTI yields reduces recombination losses and consequently increases power conversion efficiency (PCE). In addition, it gives rise to improved photoluminescence stability and improved PSC stability under illumination which can be attributed to reduced ion migration. The optimal devices exhibit a PCE of 20.67% compared to 18.89% of control devices without PBTI, while they retain over 70% of the initial efficiency after 600 h under 1 sun illumination compared to 56% for the control devices.
As
a new type of quasi-two-dimensional nanomaterial, CdSe nanoplatelets
(NPLs) possess excellent properties such as narrow emission peak,
large absorption cross section, and a low threshold of amplified spontaneous
emission. However, the origin of emission especially at low temperatures
has not been studied clearly up till now. Here, we study the temperature-dependent
photoluminescence of CdSe NPLs which show two emission peaks at low
temperatures. It is interesting to note that the intensity of the
low-energy peak shows a correlation with laser irradiation time. Moreover,
the low-temperature PL spectra of four CdSe NPLs with different lateral
sizes demonstrate the relationship of low-energy peaks with the surface.
It has been confirmed that CdSe NPLs with larger surface areas to
volume ratio have stronger low-energy emissions, which is ascribed
to the surface-state-related emission. Finally, surface passivation
of CdSe NPLs attenuates the intensity of the low-energy peak, which
further verifies our model. Our results demonstrate the critical significance
of surface in CdSe NPLs for their optical properties, which is crucial
for the application of optoelectronic devices.
Water-soluble CdSe/CdS nanocrystals stabilized using cysteine molecules exhibit efficient circular dichroism and large multiphoton absorption and show applications in two-photon fluorescence lifetime imaging and photodynamic therapy.
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