Photoluminescence Lifetimes Exceeding 8 μs and Quantum Yields Exceeding 30% in Hybrid Perovskite Thin Films by Ligand Passivation

Abstract

We study the effects of a series of post-deposition ligand treatments on the photoluminescence (PL) of polycrystalline methylammonium lead triiodide perovskite thin films. We show that a variety of Lewis bases can improve the bulk PL quantum efficiency (PLQE) and extend the average PL lifetime, ⟨τ⟩, with large enhancements concentrated at grain boundaries. Notably, we demonstrate thin-film PLQE as high as 35 ± 1% and ⟨τ⟩ as long as 8.82 ± 0.03 μs at solar equivalent carrier densities using tri-n-octylphosphine oxide-treated films. Using glow discharge optical emission spectroscopy and nuclear magnetic resonance spectroscopy, we show that the ligands are incorporated primarily at the film surface and are acting as electron donors. These results indicate it is possible to obtain thin-film PL lifetime and PLQE values that are comparable to those from single crystals by control over surface chemistry.

Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films

“…[35,37,38,[63][64][65] These reports are in agreement with our observation that especially the surface of sol-eng films with small grains and high surface defect density (evidenced by the very low PL intensity) degrades on a much faster timescale as compared to PbAc 2 . It is likely that areas of higher defect density (for example, iodine vacancies) are more susceptible to oxygen-induced degradation.…”

“…The J-V characteristics exhibit very little hysteresis and a stable power output ( Figure S2, Supporting Information) which can be attributed to the use of PCBM as an electron extraction layer. [34][35][36][37][38][39] In light of these reports, our PL results suggest that the sol-eng layer exhibits a much larger density of surface and grain boundary trap density as compared to PbAc 2 . More importantly, crosssection images (Figure 1d-e) show that for PbAc 2 the grains protrude throughout the entire film allowing charges to be transported to the extraction layers within a single grain.…”

Inversion symmetry and bulk Rashba effect in methylammonium lead iodide perovskite single crystals

“…The effective masses found here for tetragonal MAPbI 3 are comparable with those of electrons and light holes in GaAs 57 —the electron and light hole masses in GaAs are slightly smaller than those in MAPbI 3 , but the heavy hole masses in GaAs are considerably larger 57 . Commonly reported values for the non-radiative ( τ nr  = 100 ns) and radiative ( τ rad  = 2 μs) carrier lifetimes in MAPbI 3 48 , combined with the effective masses, give estimated diffusion lengths in the range of 1–10 μm, similar to values reported experimentally 13–17 and comparable with those of moderately doped GaAs 58 . Finally, both GaAs and tetragonal MAPbI 3 luminesce strongly and with a high quantum yield in surface passivated samples, clearly suggesting that the band gap of MAPbI 3 is direct 14 .…”

“…Long carrier diffusion lengths of up to 1 μm have been recognized early on as a key factor for device performance 13 , and diffusion lengths as high as tens of microns in single crystals (and more recently in polycrystalline thin films) 14–16 have been reported. The associated long carrier lifetimes of up to tens of microseconds are also particularly surprising given that MAPbI 3 films are solution processed and polycrystalline 14,17 .…”

Enhanced efficiency and stability of inverted perovskite solar cells by interfacial engineering with alkyl bisphosphonic molecules

“…As electron donors, the bisphosphonic groups could provide lone pair electrons of P atoms, which could passivate the electric trap states at the perovskite/PC 61 BM interface, reduce the recombination and facilitate the charge transfer. 44,45 Moreover, since the long alkyl chains were insulating, the effect of the interfacial treatment on the surface conductivity of perovskite lms was further studied by c-AFM (Fig. S5 †).…”