Enhanced On–Off Ratio Photodetectors Based on Lead‐Free Cs₃Bi₂I₉ Single Crystal Thin Films

Abstract

Hybrid organic–inorganic lead halide perovskite single crystal thin film (SCTF) recently has attracted enormous interest in the field of optoelectronic devices, since it efficiently resolves the trade‐off between thickness and carrier diffusion length. However, the toxicity of lead element and the instability induced by organic component still hinder its future developments. In this work, lead‐free all‐inorganic Cs3Bi2I9 SCTF with a high orientation along (00h) has been in situ grown on indium tin oxide (ITO) glass via a space‐limited solvent evaporation crystallization method. The trap density of Cs3Bi2I9 SCTF (5.7 × 1012 cm−3) is 263 folds lower than that of the polycrystalline thin film (PCTF) counterpart, together with a 5‐order‐of‐magnitude higher carrier mobility. These superior charge transfer properties enable a photoresponse on–off ratio as high as 11 000, which far surpasses that of the PCTF device by 460 folds, comparable to the lead halide perovskite. Furthermore, the Cs3Bi2I9 SCTF photodetector exhibits outstanding stability even without any encapsulation, whose initial performance is well maintained after aging 1000 h in humid air of 50% RH or continuous on–off light illumination for 20 h. This work will pave the way to produce new families of high‐performance, stable, and nontoxic perovskite SCTF for future optoelectronic applications.

Suppressing Interfacial Charge Recombination in Electron‐Transport‐Layer‐Free Perovskite Solar Cells to Give an Efficiency Exceeding 21 %

“…[33] Figure 2f depicts the dark currentvoltage (I-V)curves of the corresponding devices.Ingeneral, the linear region at low bias represents the ohmic response, followed by at rap-filling process at high bias. [33,34] Thet rapfilled limit voltage (V TFL )was estimated to be 0.39 Vfor the a-NbOH based device,3 0% lower than the Nb 2 O 5 -based counterpart (0.62 V). Thet rap-state densities can be calculated as [Eq.…”

Lead‐Free Cs3Sb2Br9 Single Crystals for High Performance Narrowband Photodetector

“…[15][16][17][18] Compared to polycrystalline films, the high-quality lead free single crystalline perovskites have advantages of long charge carrier diffusion length, low trap density, and long-range ordered patterns, [19][20][21] leading to worldwide interest in nonlead single-crystal based PDs for faster photoresponse and more effective charge extraction. [22][23][24][25][26] In this regard, millimetersized Cs 2 SnCl 6−x Br x single crystal PD with a detectivity of 2.71 × 10 10 Jones and narrow band photodetection (≈45 nm) has been demonstrated with its response spectra continuously modulated from near violet to orange by changing the halide compositions of the single crystals. [17] The Cs 3 Bi 2 I 9 single crystal thin film PD with a detectivity of 9.3 × 10 9 Jones has obtained on-off ratio as high as 11 000, which has directly contributed to the significant reduced trap density and higher carrier mobility.…”

“…[17] The Cs 3 Bi 2 I 9 single crystal thin film PD with a detectivity of 9.3 × 10 9 Jones has obtained on-off ratio as high as 11 000, which has directly contributed to the significant reduced trap density and higher carrier mobility. [22] Layered (NH 4 ) 3 Bi 2 I 9 single crystal with anisotropic response has been reported for highly sensitive X-ray detection. [23] In terms of Sb based perovskite materials, there are recent progresses on light-emitting diodes (LEDs) for violet [27] and blue emission [28] fabricated by applying stable lead-free Cs 3 Sb 2 Br 9 quantum dots, as well as enhanced photocatalytic CO 2 reduction activity based on uniform and pure Cs 3 Sb 2 Br 9 nanocrystals.…”

“…[49] The key performances of previously reported lead-free perovskite based PDs have been listed in Table 1. [15,22,50,51,44,52,53] As shown in Table 1, both Sb and Bi are trivalent ions, but it seems that Sb is more promising to produce high-performance metal halides than Bi for PD devices. The responsivity of Cs 3 Sb 2 Br 9 single crystal based PD was more than three order of magnitude higher than Cs 3 Bi 2 I 9 single crystals based PDs, [22,51] showing an excellent performance in blue light detection.…”

A Centrifugal‐Force‐Assisted Wet‐Etching Approach toward Top‐Down Fabrication of Perovskite‐Single‐Crystalline Thin Films

“…The bottom-up method means precursors grow directly into a single-crystalline film in confined space. [13][14][15][16] While, the top-down method starts with a bulk perovskite single crystal and reduces its vertical dimension via cutting and etching. The top-down method is a bit complicated than bottom-up method, but it shows significant advantages for thickness-and orientation-controllable perovskite-single-crystalline thin films.…”