Ultrasensitive Sn-Pb perovskite photodetector for monolithic near-infrared imaging

Hybrid perovskite photodetectors, the novel alternative devices transform incident light into electrical signal, have been rapidly developed in the past years. However, intrinsic unbalanced charge carrier transport within hybrid perovskite materials, restricting further boosting device performance of perovskite photodetectors, has rarely been addressed. In this study, we report room temperature–operated solution-processed bulk heterojunction perovskite photodetectors with ultrahigh sensitivity and great photo-gain. It is found that the introduction of Zn2SnO4 nanoparticles into CH3NH3PbI2.55Br0.45 perovskites results in enlarged photocurrent and suppressed dark current for bulk heterojunction perovskite photodetectors. As a result, a responsivity of over 1500 mAW−1 and projected detectivity of approximatively 1014 Jones (1 Jones = cm Hz1/2 W−1) from 380 to 760 nm are observed from bulk heterojunction perovskite photodetectors. In addition, bulk heterojunction perovskite photodetectors exhibit an excellent linear dynamic range of 124 dB and a great photo-gain of 535. All these results indicate that high-performance perovskite photodetectors could be realized through novel bulk heterojunction device structure.

Solution‐processed narrow‐bandgap Sn–Pb perovskites have shown their potential in near‐infrared (NIR) photodetection as a promising alternative to traditional silicon and inorganic compounds. To achieve efficient NIR photodetection, high‐quality Sn–Pb perovskite thick films with well‐packed, smooth, and pinhole/void‐free features are highly desirable for boosting the spectral absorption. Understanding the crystallization kinetics and tuning the crystallization are fundamentally important to reach such high‐quality thick Sn–Pb perovskite films, and have been limitedly explored. Herein, an approach of double‐side crystallization tuning through low‐temperature space‐restricted annealing in methylammonium‐free Sn–Pb perovskite films with over 1 µm thickness is proposed. More specifically, through simultaneously retarding the crystallization in the top of precursor films and promoting the crystal growth of the bottom of precursor films, high‐quality and block‐like thick FA0.85Cs0.15Sn0.5Pb0.5I3 perovskite films with improved crystallinity, preferred out‐of‐plane orientation, and reduced trap density are achieved. Finally, photovoltaic‐mode Sn–Pb perovskite NIR photodetectors show a high external quantum efficiency of ≈80% at 760–900 nm, a recorded responsivity of 0.53 A W−1, and a high specific detectivity of 6 × 1012 Jones at 940 nm. This study offers the fundamental understanding of the crystallization kinetics of thick perovskite films and paves the way for perovskite‐based emerging NIR photodetection and imaging applications.

Ultraviolet-visible-near infrared (UV-Vis-NIR) broadband detection is important for image sensing, communication, and environmental monitoring, yet remains as a challenge in achieving high external quantum efficiency (EQE) in the broad spectrum range. Herein, sensitive broadband integrated photodetectors (PDs) with high EQE levels are reported. The organic bulk-heterojunction (OBHJ) layer, based on a NIR sensitive organic acceptor, is employed to extend the response spectrum of the perovskite PDs. A key strategy of introducing dual electron transport materials respectively for Vis and NIR regions into the active layer of integrated PDs is applied. Further combined with the proper energy level alignment and reasonable distribution of PC61 BM in the active layer, the extraction and transport of photo induced charges in between perovskite and OBHJ is promoted efficiently. The integrated PD with the optimized structure exhibits an EQE mostly beyond 70% in the Vis-NIR region, which is the highest value among the ever reported solution-processable broadband PDs. The highest responsivity is 0.444 and 0.518 A W-1 in the Vis and NIR region, respectively. The specific detectivity is beyond 1010 Jones in the range from 340 to 940 nm, enabling the device to detect weak signals in the UV to NIR broad region.

The diverse biological eyes vision systems found in nature can provide attractive design inspiration for near‐infrared (NIR) imaging devices. Outstanding features of the retina are its concave hemisphere geometry and high‐sensitivity image acquisition, which simplify the optical complexity of the eye and improve the imaging quality of visual perception. However, developing high‐performance NIR biomimetic imaging systems with these characteristics is extremely challenging due to the limitations of their hemisphere‐like structures, constituent materials, and conventional imaging modules. Here, a hemispherical biomimetic eyes imaging system based on ultraflexible all‐polymer heterojunction NIR phototransistors is presented. The device features a self‐supporting ultrathin (≈659 nm) NIR imaging structure that can maintain stable photoelectric performance while adhering to the human body or arbitrary‐shaped objects and have extraordinary photosensitivity (≈106) under dim light conditions (0.038 mW cm−2, 808 nm). Based on the versatile NIR device array, hemispherical ultrasensitive NIR biomimetic eyes are successfully achieved and higher‐resolution imaging is realized. Results demonstrated in this work provide a new strategy for constructing ultraflexible and ultrasensitive NIR photodetectors, showing remarkable application potential in next‐generation visual prosthetics and intelligent bioimaging systems.

Stable and sensitive tin-lead perovskite photodetectors enabled by azobenzene derivative for near-infrared acousto-optic conversion communications

As global concern for food security continues to grow, modern monitoring technologies are playing a pyramidally crucial role in the agricultural sector. However, in the face of complex and fluctuating light requirements during crop growth, the further development of environmental monitoring technology is constrained by both the complexity and variability of environmental conditions and the limited accuracy and functionality of current light sensors. Herein, a self-powered all-inorganic tin-lead (Sn-Pb) perovskite photodetector (PD) is reported, and a novel all-in-one engineering approach utilizing benzenesulfonyl hydrazide (BSH) is incorporated to effectively enhance the photodetection performance of the PD. The BSH molecule plays a pivotal role in balancing and mitigating crystallization and grain growth processes of Sn-Pb perovskite, while also inhibiting the oxidation of Sn2+ and the formation of Sn vacancy defects in perovskite film. Consequently, the optimized champion PD reaches a responsivity of 0.36 A W-1 and a detectivity of 1.74 × 1013 Jones at 650 nm. Benefitting from its excellent performance, the prototype of a light sensor employing PDs achieves specific detection of red and blue light in a simulated lighting environment required for plants development. This research not only presents a feasible strategy to improve photodetection performance of Sn-Pb perovskite PDs but also provides novel insights for designing monitoring and feedback systems in intelligent agriculture applications.

In article number 2001534, Liang Shen and co-workers demonstrate a sensitive and stable Sn-Pb perovskite photodetector, employing phenethylammonium iodide to complete defects passivation aiming the top and bottom of films. The double-sided surface passivation engineering can promote the grain growth, reduce the density of trap states and improve surface hydrophobicity. Finally, it realizes infrared up-conversion application for visualization.

Multispectral imaging plays an important role in many applications such as color recognition, substance distinction, and medical therapy. Although multicolor detection has been demonstrated in lead‐based perovskites, the limited near‐infrared responsivity and slow response impede their applications for identifying the substance. Herein, narrow bandgap highly stable Cs0.05MA0.45FA0.5Sn0.5Pb0.5I3 (Sn‐Pb) perovskite films with excellent crystallinity and selective growth orientation are realized by the synergy of a Sn‐Pb mixing method and electronegativity balance. The Sn‐Pb perovskite photodetector shows a broadband response from 350 to 1000 nm and high‐performance near‐infrared (NIR) detection with a fast response of 2.0 µs and excellent responsivity of 0.29 A W−1. Furthermore, flexible Sn‐Pb perovskite devices without any encapsulation in the air continuously exhibit fast response after 3000 bending cycles. In addition, the Sn‐Pb perovskite diffuse reflection imaging system is demonstrated for multispectral imaging and substance distinction. Meanwhile, foreign‐body identification in biological tissues by NIR imaging of Sn‐Pb perovskite photodetectors is further demonstrated, proving narrow bandgap mixed perovskite photodetectors an attractive candidate for biomedical imaging.

Tin(Sn)-based perovskite is currently considered one of the most promising materials due to extending the absorption spectrum and reducing the use of lead (Pb). However, Sn2+ is easily oxidized to Sn4+ in atmosphere, causing more defects and degradation of perovskite materials. Herein, double-sided interface engineering is proposed, that is, Sn-Pb perovskite films are sandwiched between the phenethylammonium iodide (PEAI) in both the bottom and top sides. The larger organic cations of PEA+ are arranged into a perovskite surface lattice to form a 2D capping layer, which can effectively prevent the water and oxygen to destroy bulk perovskite. Meanwhile, the PEA+ can also passivate defects of iodide anions at the bottom of perovskite films, which is always present but rarely considered previously. Compared to one sided passivation, Sn-Pb hybrid perovskite photodetectors contribute a significant enhancement of performance and stability, yielding a broadband response of 300-1050 nm, a low dark current density of 1.25 × 10-3 mA cm-2 at -0.1 V, fast response speed of 35 ns, and stability beyond 240 h. Furthermore, the Sn-Pb broadband photodetectors are integrated in an infrared up-conversion system, converting near-infrared light into visible light. It is believed that a double-sided passivation method can provide new strategies to achieving high-performance perovskite photodetectors.

Low-bandgap tin (Sn)-lead (Pb) halide perovskites can achieve near-infrared response for photodetectors. However, the Sn-based devices suffer from notorious instability and high defect densities due to the oxidation propensity of Sn2+ . Herein, a multifunctional additive 4-amino-2,3,5,6-tetrafluorobenzoic acid (ATFBA) is presented, which can passivate surface defects and inhibit the oxidation of Sn2+ through hydrogen bonds and chelation coordination from the terminal amino and carboxyl groups. The perfluorinated benzene ring structure of ATFBA affords the passivator assembled at the grain boundaries to enhance the water resistance. With the synergistical passivation of these functional groups, the Sn-Pb perovskite photodetector exhibits a remarkable responsivity of 0.52AW-1 and an excellent specific detectivity of 5.34×1012 Jones at 850nm, along with remaining 97% of its initial responsivity over 450 days. Benefitting from high sensitivity, the photodetector is integrated into a pulse oximetry sensor visualization system, yielding accurate blood oxygen saturation and heart rate with less than 2% error. This work paves the avenue toward constructing high-performance and stable Sn-Pb perovskite photodetectors for practical applications.

Tin–lead perovskite-based photodetectors have a wide light-absorption wavelength range, which spans 1000 nm. However, the preparation of the mixed tin–lead perovskite films faces two great obstacles, namely easy oxidation of Sn2+ to Sn4+ and fast crystallization from tin–lead perovskite precursor solutions, thus further resulting in poor morphology and high density of defects in tin–lead perovskite films. In this study, we demonstrated a high-performance of near-infrared photodetectors prepared from a stable low-bandgap (MAPbI3)0.5(FASnI3)0.5 film modified with 2-fluorophenethylammonium iodide (2-F-PEAI). The addition engineering can efficiently improve the crystallization of (MAPbI3)0.5(FASnI3)0.5 films through the coordination binding between Pb2+ and N atom in 2-F-PEAI, and resulting in a uniform and dense (MAPbI3)0.5(FASnI3)0.5 film. Moreover, 2-F-PEAI suppressed Sn2+ oxidation and effectively passivated defects in the (MAPbI3)0.5(FASnI3)0.5 film, thereby significantly reducing the dark current in the PDs. Consequently, the near-infrared photodetectors showed a high responsivity with a specific detectivity of over 1012 Jones at 800 to near-1000 nm. Additionally, the stability of PDs incorporated with 2-F-PEAI has been significantly improved under air conditions, and the device with the 2-F-PEAI ratio of 400:1 retained 80% of its initial efficiency after 450 h storage in air without encapsulation. Finally, 5 × 5 cm2 photodetector arrays were fabricated to demonstrate the potential utility of the Sn–Pb perovskite photodetector in optical imaging and optoelectronic applications.

The demand for self-powered, broadband photodetectors is rising in fields like artificial intelligence, health monitoring, and optical communications. However, conventional perovskite photodetectors face limited visible absorption and poor ambient stability. Here, we report a high-performance integrated photodetector combining a perovskite (Csn.15FAn.85PbI3) absorber with an organic bulk-heterojunction (BHJ) structure for broadband photon harvesting up to 1000 nm. The device achieves a peak external quantum efficiency (EQE) of 84% in the visible range (400-700 nm) and 63% in the near-infrared (NIR, 700-1000 nm). Benefiting from optimized energy band alignment, the photodetector exhibits a self-powered responsivity of 0.3 A W-1 and a fast response time of 29 µs, with a linear dynamic range (LDR) of 122 dB under 900 nm NIR illumination. The BHJ organic layer suppresses the dark current (JD) to 6.9 × 10-11 A cm-2 and noise current (in) to 10-14 A Hz-1/2, yielding a specific detectivity (D*) of 1012 Jones. The polymeric BHJ also enhances flexibility, enabling a reliable 25-pixel array for uniform NIR imaging. In optical communication, the device achieves a low bit error rate with data rates of 90 kbps (λ = 665 nm) and 140 kbps (λ = 904 nm). This work establishes the perovskite/BHJ detector as a promising platform for flexible, high-speed optoelectronics.