Understanding the Essential Role of PbI₂ Films in a High-Performance Lead Halide Perovskite Photodetector

Abstract

Hybrid lead halide perovskites fabricated via solution processing have been regarded as a promising candidate for next-generation optoelectronic devices owing to their outstanding optoelectronic properties and low fabrication cost. However, the morphology, location, and effects of residual PbI 2 in the solution process-based perovskite films are still ambiguous. Herein, by applying the time-of-flight polarized neutron reflectometer (TPNR), we uncover that the highly uniform PbI 2 film locates at the bottom of perovskite films. First-principle calculations demonstrate that the PbI 2 film in the interface between the perovskite film and contact layer can significantly reduce interface charge recombination via the carrier confinement effect owing to the higher conduction band minimum (CBM) and lower valence band maximum (VBM) of PbI 2 than those of the perovskite. To explore the essential role of PbI 2 films in the perovskite, we fabricated a photodetector based on perovskite/PbI 2 (∼534 nm/40 nm) and found its improved performances with a high optical responsivity of ∼1302 AW −1 and a rapid response speed of ∼2 ms, revealing the critical passivation role of PbI 2 . This work provides a rational design strategy for PbI 2 film thickness control in the high-performance planar optoelectronic devices with a varied structure.

Inhibition of buried cavities and defects in metal halide perovskite photodetectors via a two-step spin-coating method

“…Hence, the perovskite films prepared via the typical two-step procedure commonly suffer from an inhomogeneous thickness, featuring residual PbI 2 and irregular nanocavities at the buried interface. This phenomenon was discussed in recent reports, 20,31,33–35,37,40,44 which became more obvious as the concentration of the PbI 2 precursor increased, as shown in Fig. S1 (ESI†).…”

Intragap State Engineering for Tunable Single-Photon Upconversion Photoluminescence of Lead Halide Perovskite

“…Now one may anticipate that the SPUC-PL properties of the perovskite films can be optimized by engineering the band structure of the Urbach tail, for example, via a feasible thermal annealing protocol. − The X-ray diffraction (XRD) patterns of the perovskite films fabricated with three different annealing temperatures are illustrated in Figure a (see Figure S4 for the morphological characterizations). It shows that the characteristic peaks of the perovskite and the residual PbI 2 are respectively enhanced and reduced as the temperature decreases from 150 to 80 °C . Further electric studies (space charge limited current, Figure S5, and electrochemical impedance spectroscopy, Figure S6) testify that a low annealing temperature is favorable for preparing perovskite polycrystalline film with fewer defect states.…”

High-Light-Tolerance PbI2 Boosting the Stability and Efficiency of Perovskite Solar Cells

“…Organic–inorganic lead halide perovskite materials have outstanding properties such as high carrier mobility, a high absorption coefficient, ingredient diversity, and ease of fabrication. − Thanks to numerous devoted efforts, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has expeditiously climbed to over 25% by employing element substitution, morphology-manipulating strategies, and interface-engineering methods. − The PSC is thus considered one of the most promising photovoltaic technologies. − Among the proposed strategies, introducing excess lead iodide (PbI 2 ) is demonstrated as an effective and facile method to improve the quality of perovskite films and increase the PCE. − PbI 2 could passivate the defects on the grain boundaries of perovskite crystals and suppress the charge trapping while the PSC is under operation.…”

“…Despite the benefits to the PCE, the utilization of excess PbI 2 goes against the stability of PSCs since the simultaneously formed large PbI 2 crystals are easily decomposed to metallic Pb and gaseous I 2 through photolysis. , The simultaneously generated voids and defect points obstruct the charge collection, cause the quench of carriers, and diminish the PCE of perovskite solar cells. − They also act as transporting channels for moisture and oxygen and function as the reactive site of perovskite films as well. , The phase stability of the perovskite crystal is thus greatly reduced, accordingly leading to the shortened lifetime of PSCs and the weakened operation stability. , …”