Correlation between Photoluminescence and Carrier Transport and a Simple In Situ Passivation Method for High-Bandgap Hybrid Perovskites

Abstract

High-bandgap mixed-halide hybrid perovskites have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed a ligand-assisted crystallization (LAC) technique that introduces additives in situ during the solvent wash and developed a new method to dynamically measure the absolute intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of material changes and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation. Further, the measurements enabled optimization of LAC on the 1.75 eV bandgap FACsPb(IBr), resulting in an enhancement of the photoluminescence quantum yield (PLQY) of over an order of magnitude, an increase of 80 meV in the quasi-Fermi level splitting (to 1.29 eV), an increase in diffusion length by a factor of 3.5 (to over 1 μm), and enhanced open-circuit voltage and short-circuit current from photovoltaics fabricated from the LAC-treated films.

Effect of halide ratio and Cs+ addition on the photochemical stability of lead halide perovskites

“…60 Regardless of the mechanism it is generally agreed that Cs + decreases the tendency for phase separation. 29,30,56,61 Our results clearly show that addition of Cs + can limit ion migration. It is therefore possible to signicantly increase the intrinsic photostability of lead halides perovskites by optimising the A-site cation composition and the Br : I ratio.…”

Maximizing and stabilizing luminescence from halide perovskites with potassium passivation

“…We demonstrate external photo-luminescence quantum yields of 66%, translating to internal yields exceeding 95%. The high luminescence yields are achieved while maintaining high mobilities over 40 cm 2 V -1 s -1 , giving the elusive combination of both high luminescence and excellent charge transport 10 . We find that the external luminescence yield when interfaced with electrodes in a solar cell device stack, a quantity that must be maximised to approach the efficiency limits, remains as high as 15%, indicating very clean interfaces.…”

“…We use time-resolved microwave conductivity (TRMC) to assess the impact of the passivation on charge transport in the (Cs,FA,MA)Pb(I0.85Br0.15)3 perovskite thin films (Extended Data Figure 5) 10,18 . In Figure 1c, we show the maximum photo-conductance (charge mobility) for each of the K contents.…”

Shining Light on the Photoluminescence Properties of Metal Halide Perovskites

“…At present, however, the same perovskite composition excited by the same power density is reported to have different values for the PLQE depending on the group ( Figure ). [ 37–48 ] Not only is this suggestive of reproducibility issues which are known to plague perovskites, including varying light outcoupling efficiency and subtle differences in the defect content, but, in light of numerous reports to be discussed in this review, it is suggestive of varying measurement conditions. Therefore, in this review, we discuss the current state of understanding of photoluminescence measurements in perovskite materials for optoelectronic applications with an emphasis on unifying results and interpretations across the field.…”