Transient Energy-Resolved Photoluminescence Study of Excitons and Free Carriers on FAPbBr₃ and FAPbBr₃/SnO₂ Interfaces

Abstract

Lead bromide perovskites have a larger band gap and are significantly more stable than their iodine counterparts, offering the perspective for higher voltage, tandem photovoltaics exceeding the Shockley−Queisser limit, and shorter time to deployment of photovoltaics. However, their efficiencies still need to be rivaling the iodine ones. Herein, the photophysics of FAPbBr 3 and the ones behind electron transfer from FAPbBr 3 to SnO 2 , one of the most effective electron transporting materials (ETMs), are reported. Time-and energy-resolved photoluminescence studies revealed the existence of two emitting states in the perovskite, which were assigned to bounded excitons and free carriers. SnO 2 extracted electrons from excitons and free carriers, with a selectivity related to the SnO 2 surface treatment. This new insight helps explain SnO 2 's unique qualities as an ETM to produce photovoltaics with reduced voltage losses. Furthermore, this study illustrates the importance of performing time-and energy-resolved photoluminescence to capture the intricacies of the photophysical process.

Can photoluminescence quenching be a predictor for perovskite solar cell efficiencies?

“…Based on our previous study, 37 deconvolutions of the PL spectrum revealed two peaks resulting from the recombination of free carriers (high energy emission, in the presence study ca. 520 nm) and excitons (low energy emission, in the presence study ca.…”

“…FAPbBr 3 is a wide-band gap perovskite (around 2.2 eV) with a cubic crystal structure after thermal annealing. 37 Compared with the FAPbI 3 perovskite, the FAPbBr 3 counterpart has a higher exciton binding energy, ranging from 24 to 80 meV. 38,39 Previously, we estimated our exciton binding energy to be ca.…”

“…60 meV. 37 Therefore, with an excitation energy of 2.4 eV ( i.e. 515 nm), the coexistence of free charges and bounded excitons in FAPbBr 3 is to be expected.…”

Enhanced Photoluminescence and Random Lasing Emission in TiO2-Decorated FAPbBr3 Thin Films

“…The photoluminescence peak position could be attributed to different factors, such as the reabsorption and recycling of light, the temperature of the thin films, the grain size of the perovskite crystals, reabsorption combined with carrier diffusion, multiple scattering of light from disordered grain boundaries, and scattering centers of the TiO 2 nanoparticle clusters [58]. In this work, the granularity changes in the FAPbBr 3 perovskite grains play an essential role in the photoluminescence emission intensities and the emission peak centers [59]. In addition, the multiple scattering of light from the TiO 2 nanoparticle clusters increases the light path thickness within the perovskite thin films, where the reabsorption and recycling of light and multiple reflections could occur.…”

Indoline‐Based Dopant‐Free Hole Transporting Material with Edge‐on Orientation for High Performance Perovskite Solar Cells

“…To quantify the hole extracted ability of HTMs in high current region, the normalized PL band edge shifts were analyzed. [32] Despite the blueshift of PL peaks are observed in the BDT-p-IDN and BDT-DPA-F capped films when current increased from 0.3 to 0.4 A (Figure 3f and S20, Supporting Information), the BDT-p-IDN/PVK film shows a smaller PL band edge shift (Figure S21b, Supporting Information). These results indicate that BDT-p-IDN is more effective to extract hole from PVK layer.…”