Millimeter-Sized Single-Crystal CsPbrB3/CuI Heterojunction for High-Performance Self-Powered Photodetector

A bromide substituted 2D additive for stable and efficient perovskite photovoltaics

In this article, a bromide substituted 2D layered perovskite having a repeated vertical orientation and coexisting with the bulk of a 3D perovskite is reported for the first time. This novel structure is obtained through controlled compositional engineering of the perovskite precursor solution. The photovoltaic performance of this novel 2D/3D perovskite was higher than that of 3D MAPbI3 and a maximum photoconversion efficiency (PCE) of 17.4% was achieved. The devices fabricated using this perovskite heterostructure were stable and retained their initial PCE up to 20 days when kept open in a laboratory environment with 40% relative humidity.

Fabrication of two Se/CsPbBr3 heterojunctions structures for self-powered UV-visible photodetectors

It has been a universal route for enhanced photoelectric performance in photodetectors by constructing a heterojunction that is conductive for suppressing recombination of photogenerated carriers and promoting collection efficiency, and probably producing self-powered capability. However, the dependence of the built-in electric field distributions created by the heterojunction on photodetector performance has rarely been investigated. Herein, two kinds of self-powered UV-visible photodetectors with different device architectures based on single Se wire and CsPbBr3 particles are facilely fabricated and compared. It is found that both the two photodetectors show excellent self-powered operating properties, fast response and binary response. However, due to the different distributions of built-in electric field caused by device architectures, it yields a significant photovoltaic voltage distinction and different responsivity and detectivity spectra for the Se/CsPbBr3 photodetectors. These results are conductive to guide the design of self-powered heterojunction photodetectors by regulating the built-in electric field distributions.

Flexible Self-Powered Weak Light Detectors Based on ZnO/CsPbBr3/γ-CuI Heterojunctions

Halide perovskites (HPs) with marvelous optical and electrical properties are regarded as one of the competitive candidates for building next-generation photodetectors (PDs). However, combining their excellent properties with satisfactory long-term robustness is still challenging, ultimately limiting the practical applications of HP-based PDs. Herein, a high vacuum deposition system is employed to fabricate flexible self-powered PDs with a ZnO/CsPbBr₃/γ-CuI structure, which shows excellent stability and outstanding performance in weak light detection. Benefiting from the improved crystallinity and optimized device structure, a high detectivity of 8.1 × 10¹³ Jones and a rapid response speed (rise/decay time of 3.9/1.8 μs) are obtained in this self-powered device. Furthermore, the unencapsulated device exhibits intriguing environmental stability and mechanical flexibility. The photocurrent remains unchanged after 7000 s of continuous operation or 100 bending cycles. Furthermore, a 15 × 15 PD array is fabricated as an image sensor. A high contrast image of the target object can be obtained owing to the high sensitivity and uniformity of the self-powered PDs. These results demonstrate the feasibility and practicality of the ZnO/CsPbBr₃/γ-CuI heterojunction for applications in weak light detection and image formation.

Self-powered p-CuI/n-GaN heterojunction UV photodetector based on thermal evaporated high quality CuI thin film

With vacuum thermal evaporation, the CuI film was deposited on quartz and n-GaN substrates, and the morphology, crystalline structure and optical properties of the CuI films were investigated. According to the XRD results, the CuI film preferentially grew along [111] crystal orientation on the GaN epilayer. With Au and Ni/Au ohmic contact electrodes fabricated on CuI and n-GaN, a prototype p-CuI/n-GaN heterojunction UV photodetector strong UV spectral selectivity was created. At 0 V and 360 nm front illumination (0.32 mW/cm²), the heterojunction photodetector displayed outstanding self-powered detection performance with the responsivity (R), specific detectivity (D*), and on/off ratio up to 75.5 mA/W, 1.27×10¹² Jones, and ∼2320, respectively. Meanwhile, the p-CuI/n-GaN heterojunction photodetector had excellent atmosphere stability.

A vertical CsPbBr3/ZnO heterojunction for photo-sensing lights from UV to green band

In this work, we have reported a vertical CsPbBr₃/ZnO heterojunction photodetector for photo-sensing lights from UV to visible band. The ZnO thin film is deposited on the c-sapphire substrate through a molecular beam epitaxy (MBE) technique, and then the CsPbBr₃ thin film is synthesized on the as-prepared ZnO film layer by using a solution processing method. The as-prepared CsPbBr₃/ZnO heterostructure presents type-II energy band structure induced by the energy band offset effect, which can promote the separation and extraction efficiencies of the photo-generated electron-hole pairs. Compared with the CsPbBr₃ based metal-semiconductor-metal (MSM) structure photodetector, the heterojunction photodetector presents higher responsivity and detectivity of 630 µA/W and 7 × 10⁹ Jones. While compared with the ZnO based MSM structure photodetector, the heterojunction device reveals much faster response speeds of 61 µs (rise time) and 1.4 ms (decay time). These findings demonstrate that the CsPbBr₃/ZnO heterojunction photodetector is promising for constructing next generation perovskite based optoelectronic devices.

Origin of the anisotropic-strain-driven photoresponse enhancement in inorganic halide-based self-powered flexible photodetectors

Strain engineering has been recognized as a critical strategy in modulating the optoelectronic properties of perovskite halide materials. Here, we demonstrate a self-powered, flexible photodetector based on CsPbBr₃ thin films with controllable compressive or tensile strain of up to ±0.81%, which was produced in situ via a sequential two-step deposition on bent polymer substrates. The best photoresponsivity of ∼121.5 mA W^-1 with a photocurrent of 5.15 μA was achieved at zero bias under a power intensity of 0.47 mW cm^-2 for the maximum tensile strain of +0.81%, which corresponds to a ∼100.2% increase relative to that of the unstrained case. The in situ tensile strain adjusted the band alignments, making them favorable for enhanced charge transport and thus a higher photoresponse. The structural origin of this superlative balanced photodetection performance was systematically revealed to be associated with the distortion of coupled PbBr₆ octahedra and the atomic displacement within the octahedron.

In situ construction of a Te/CsPbBr3 heterojunction for self-powered photodetector

In this study, CsPbBr3 particles were prepared by a simple solvent evaporation method in ambient environment; the p-n heterojunction formed by CsPbBr3 particles on the surface of a single long Te wire was used to construct a high-performance Te/CsPbBr3 photodetector. Compared with CsPbBr3 PDs, the Te/CsPbBr3 photodetector showed improved photocurrent, and exhibited characteristics of excellent self-powered performance, broad-spectrum response (UV-visible), and ultra-fast response speed (t rise = 0.09 ms). In addition, under zero bias and upon 540 nm light irradiation, the device had good responsivity (0.35 mA W-1), high photosensitivity (up to 100 on/off ratio), and a detectivity of 1.42 × 1010 Jones. This study provides insight into the possibility of manufacturing high-performance self-powered photodetectors through a simple in situ construction of heterojunctions.

Controllable vapor growth of CsPbBr3/CdS 1D heterostructures with type-II band alignment for high-performance self-powered photodetector

The controllable growth of CsPbBr3/CdS heterostructures with a unique 1D morphology and type-II band alignment for a high-performance self-powered photodetector.

Dramatic Responsivity Enhancement Through Concentrated H2 SO4 Treatment on PEDOT:PSS/TiO2 Heterojunction Fibrous Photodetectors

In order to satisfy the growing requirements of wearable electronic devices, 1D fiber-shaped devices with outstanding sensitivity, flexibility, and stability are urgently needed. In this study, a novel inorganic-organic heterojunction fibrous photodetector (FPD) based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and highly ordered TiO₂ nanotube array is fabricated, which endows a high responsivity, large external quantum efficiency, and fast response speed at 3 V bias. To further ameliorate its performance in the self-powered mode, a facile acid treatment is adopted and the assembled H-PEDOT:PSS/TiO₂ FPD demonstrates outstanding self-powered properties with ≈3000% responsivity enhancement (161 mA W^-1 at 0 V under 365 nm irradiation, photocurrent enhancement of ≈50 times) compared with the untreated device. It is found that the concentrated H₂ SO₄ post-treatment helps decrease the tube wall thickness of TiO₂ and partially removes the insulated PSS component in PEDOT:PSS, leading to enhanced conductivity and facilitated charge transportation, and thereby superb responsivity/photocurrent enhancement of self-powered H-PEDOT:PSS/TiO₂ FPD. This low-cost and high-performance self-powered FPD shows high potential for applications in wearable electronic devices.

Engineering Copper Iodide (CuI) for Multifunctional p-Type Transparent Semiconductors and Conductors

Developing transparent p-type semiconductors and conductors has attracted significant interest in both academia and industry because metal oxides only show efficient n-type characteristics at room temperature. Among the different candidates, copper iodide (CuI) is one of the most promising p-type materials because of its widely adjustable conductivity from transparent electrodes to semiconducting layers in transistors. CuI can form thin films with high transparency in the visible light region using various low-temperature deposition techniques. This progress report aims to provide a basic understanding of CuI-based materials and recent progress in the development of various devices. The first section provides a brief introduction to CuI with respect to electronic structure, defect states, charge transport physics, and overviews the CuI film deposition methods. The material design concepts through doping/alloying approaches to adjust the optoelectrical properties are also discussed in the first section. The following section presents recent advances in state-of-the-art CuI-based devices, including transparent electrodes, thermoelectric devices, p-n diodes, p-channel transistors, light emitting diodes, and solar cells. In conclusion, current challenges and perspective opportunities are highlighted.

Recent Progress on Electrical and Optical Manipulations of Perovskite Photodetectors

Photodetectors built from conventional bulk materials such as silicon, III-V or II-VI compound semiconductors are one of the most ubiquitous types of technology in use today. The past decade has witnessed a dramatic increase in interest in emerging photodetectors based on perovskite materials driven by the growing demands for uncooled, low-cost, lightweight, and even flexible photodetection technology. Though perovskite has good electrical and optical properties, perovskite-based photodetectors always suffer from nonideal quantum efficiency and high-power consumption. Joint manipulation of electrons and photons in perovskite photodetectors is a promising strategy to improve detection efficiency. In this review, electrical and optical characteristics of typical types of perovskite photodetectors are first summarized. Electrical manipulations of electrons in perovskite photodetectors are discussed. Then, artificial photonic nanostructures for photon manipulations are detailed to improve light absorption efficiency. By reviewing the manipulation of electrons and photons in perovskite photodetectors, this review aims to provide strategies to achieve high-performance photodetectors.

Characteristics and Electronic Band Alignment of a Transparent p-CuI/n-SiZnSnO Heterojunction Diode with a High Rectification Ratio

Transparent p-CuI/n-SiZnSnO (SZTO) heterojunction diodes are successfully fabricated by thermal evaporation of a (111) oriented p-CuI polycrystalline film on top of an amorphous n-SZTO film grown by the RF magnetron sputtering method. A nitrogen annealing process reduces ionized impurity scattering dominantly incurred by Cu vacancy and structural defects at the grain boundaries in the CuI film to result in improved diode performance; the current rectification ratio estimated at ±2 V is enhanced from ≈10⁶ to ≈10⁷. Various diode parameters, including ideality factor, reverse saturation current, offset current, series resistance, and parallel resistance, are estimated based on the Shockley diode equation. An energy band diagram exhibiting the type-II band alignment is proposed to explain the diode characteristics. The present p-CuI/n-SZTO diode can be a promising building block for constructing useful optoelectronic components such as a light-emitting diode and a UV photodetector.

Low-Dimensional Metal Halide Perovskite Photodetectors

Metal halide perovskites (MHPs) have been a hot research topic due to their facile synthesis, excellent optical and optoelectronic properties, and record-breaking efficiency of corresponding optoelectronic devices. Nowadays, the development of miniaturized high-performance photodetectors (PDs) has been fueling the demand for novel photoactive materials, among which low-dimensional MHPs have attracted burgeoning research interest. In this report, the synthesis, properties, photodetection performance, and stability of low-dimensional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as well as their heterostructures are reviewed. Recent advances in the synthesis approaches of low-dimensional MHPs are summarized and the key concepts for understanding the optical and optoelectronic properties related to the PD applications of low-dimensional MHPs are introduced. More importantly, recent progress in novel PDs based on low-dimensional MHPs is presented, and strategies for improving the performance and stability of perovskite PDs are highlighted. By discussing recent advances, strategies, and existing challenges, this progress report provides perspectives on low-dimensional MHP-based PDs in the future.

Broadband Ultraviolet Self-Powered Photodetector Constructed on Exfoliated β-Ga2O3/CuI Core-Shell Microwire Heterojunction with Superior Reliability

A heterojunction is an essential strategy for multispectral energy-conservation photodetection for its ability to separate photogenerated electron-hole pairs and tune the absorption edge by selecting semiconductors with appropriate bandgaps. A broadband ultraviolet (200-410 nm) self-powered photodetector is constructed on the exfoliated β-Ga₂O₃/CuI core-shell microwire heterostructure. Benefiting from the photovoltaic and photoconductive effects, our device performs an excellent ultraviolet (UV) discriminability with a UVC/visible rejection ratio (R₂₂₅/R₆₀₀) of 8.8 × 10³ and a UVA/visible rejection ratio (R₄₀₀/R₆₀₀) of 2.7 × 10², and a self-powered photodetection with a responsivity of 8.46 mA/W, a detectivity of 7.75 × 10¹¹ Jones, an on/off switching ratio of 4.0 × 10³, and a raise/decay speed of 97.8/28.9 ms under UVC light. Even without encapsulation, the photodetector keeps a superior stability over ten months. The intrinsically physical insights of the device behaviors are investigated via energy band diagrams, and the charge carrier transfer characteristics of the β-Ga₂O₃/CuI interface are predicted by first principle calculation.

Additive Modulated Perovskite Microstructures for High Performance Photodetectors

Organic-inorganic hybrid perovskites have been widely used as light sensitive components for high-efficient photodetectors due to their superior optoelectronic properties. However, the unwanted crystallographic defects of perovskites typically result in high dark current, and thus limit the performance of the device. Herein, we introduce a simple route of microstructures control in MAPbI₃ perovskites that associates with introducing an additive of 3,3,4,4-benzophenonetetracarboxylic dianhydridean (BPTCD) for crystallization adjustment of the perovskite film. The BPTCD additive can facilitate the formation of high-quality perovskite film with a compact and nearly pinhole-free morphology. Through characterizing the molecular interactions, it was found that the carbonyl groups in BPTCD is the key reason that promoted the nucleation and crystallization of MAPbI₃. As a result, we obtained high-efficient and stable perovskite photodetectors with low dark current of 9.98 × 10^-8 A at -0.5 V, an on/off ratio value of 10³, and a high detectivity exceeding 10¹² Jones over the visible region.

Red Light-Emitting Diodes with All-Inorganic CsPbI3/TOPO Composite Nanowires Color Conversion Films

This work presents a method for obtaining a color-converted red light source through a combination of a blue GaN light-emitting diode and a red fluorescent color conversion film of a perovskite CsPbI3/TOPO composite. High-quality CsPbI3 quantum dots (QDs) were prepared using the hot-injection method. The colloidal QD solutions were mixed with different ratios of trioctylphosphine oxide (TOPO) to form nanowires. The color conversion films prepared by the mixed ultraviolet resin and colloidal solutions were coated on blue LEDs. The optical and electrical properties of the devices were measured and analyzed at an injection current of 50 mA; it was observed that the strongest red light intensity was 93.1 cd/m2 and the external quantum efficiency was 5.7% at a wavelength of approximately 708 nm when CsPbI3/TOPO was 1:0.35.

Highly UV Resistant Inch-Scale Hybrid Perovskite Quantum Dot Papers

Halide perovskite quantum dots (PQDs) are promising materials for diverse applications including displays, light-emitting diodes, and solar cells due to their intriguing properties such as tunable bandgap, high photoluminescence quantum yield, high absorbance, and narrow emission peaks. Despite the prosperous achievements over the past several years, PQDs face severe challenges in terms of stability under different circumstances. Currently, researchers have overcome part of the stability problem, making PQDs sustainable in water, oxygen, and polar solvents for long-term use. However, halide PQDs are easily degraded under continuous irradiation, which significantly limits their potential for conventional applications. In this study, an oleic acid/oleylamine (traditional surface ligands)-free method to fabricate perovskite quantum dot papers (PQDP) is developed by adding cellulose nanocrystals as long-chain binding ligands that stabilize the PQD structure. As a result, the relative photoluminescence intensity of PQDP remains over ≈90% under continuous ultraviolet (UV, 16 W) irradiation for 2 months, showing negligible photodegradation. This proposed method paves the way for the fabrication of ultrastable PQDs and the future development of related applications.

Illumination-Induced Phase Segregation and Suppressed Solubility Limit in Br-Rich Mixed-Halide Inorganic Perovskites

Mixing halides in perovskites has emerged as an effective strategy for tuning the band gap for optoelectronic applications and tackling the stability bottleneck. However, notable photoluminescence evolution has been observed in mixed-halide perovskites under external stimuli such as light illumination, which is attributed to phase segregation with halide inhomogeneity. In this work, we investigate the light illumination effect on the optical properties of all-inorganic mixed-halide perovskite CsPb(Br_1-xI_x)₃ in the Br-rich regime. It is found that the critical iodine concentration, defined as the solubility limit against phase segregation, is significantly suppressed by light illumination to an extremely low level (x < 0.025), although the formation energy calculation suggests a wide range of halide mixing. Furthermore, at high I concentrations (x ≥ 0.2), the phase segregation can be rectified via dark storage within 1 h, but much slower and incomplete reversibility is observed at lower I concentrations. In the all-inorganic mixed-halide perovskite films, the light-induced phase segregation above the solubility limit is also accompanied by a monotonous increase in fluorescence lifetime. Last, we propose that light-induced phase segregation enables the potential application of encrypting erasable information in perovskite films with the aid of tailored light exposure and photoluminescence mapping.

Enhanced stability in CH3NH3PbI3 hybrid perovskite from mechano-chemical synthesis: structural, microstructural and optoelectronic characterization

Among the hybrid organic-inorganic perovskites MAPbX₃ (MA: methyl-ammonium CH₃-NH₃⁺, X = halogen), the triiodide specimen (MAPbI₃) is still the material of choice for solar energy applications. Although it is able to absorb light above its 1.6 eV bandgap, its poor stability in humid air atmosphere has been a major drawback for its use in solar cells. However, we discovered that this perovskite can be prepared by ball milling in a straightforward way, yielding specimens with a superior stability. This fact allowed us to take atomic-resolution STEM images for the first time, with sufficient quality to unveil microscopic aspects of this material. We demonstrated full Iodine content, which might be related to the enhanced stability, in a more compact PbI₆ framework with reduced unit-cell volume. A structural investigation from neutron powder diffraction (NPD) data of an undeuterated specimen was essential to determine the configuration of the organic MA unit in the 100-298 K temperature range. A phase transition is identified, from the tetragonal structure observed at RT (space group I4/mcm) to an orthorhombic (space group Pnma) phase where the methyl-ammonium organic units are fully localized. Our NPD data reveal that the MA changes are gradual and start before reaching the phase transition. Optoelectronic measurements yield a photocurrent peak at an illumination wavelength of 820 nm, which is redshifted by 30 nm with respect to previously reported measurements on MAPbI₃ perovskites synthesized by crystallization from organic solvents.

Void-free 3D Bioprinting for In-situ Endothelialization and Microfluidic Perfusion

Two major challenges of 3D bioprinting are the retention of structural fidelity and efficient endothelialization for tissue vascularization. We address both of these issues by introducing a versatile 3D bioprinting strategy, in which a templating bioink is deposited layer-by-layer alongside a matrix bioink to establish void-free multimaterial structures. After crosslinking the matrix phase, the templating phase is sacrificed to create a well-defined 3D network of interconnected tubular channels. This void-free 3D printing (VF-3DP) approach circumvents the traditional concerns of structural collapse, deformation and oxygen inhibition, moreover, it can be readily used to print materials that are widely considered "unprintable". By pre-loading endothelial cells into the templating bioink, the inner surface of the channels can be efficiently cellularized with a confluent endothelial layer. This in-situ endothelialization method can be used to produce endothelium with a far greater uniformity than can be achieved using the conventional post-seeding approach. This VF-3DP approach can also be extended beyond tissue fabrication and towards customized hydrogel-based microfluidics and self-supported perfusable hydrogel constructs.

Self-powered, all-solution processed, trilayer heterojunction perovskite-based photodetectors

Heterostructures composed of nano-/micro-junctions, combining the excellent photon harvesting properties of nano-systems and the ultrafast carrier transfer of micro-systems, have a promising role in high-performance photodetectors. In this paper, a highly-sensitive trilayer self-powered perovskite-based photodetector ITO/ZnO (70 nm)/CdS (150 nm)/CsPbBr₃ (200 nm)/Au, in which the CdS nanorods (NRs) layer is sandwiched between a ZnO/CsPbBr₃ interface to reduce the interfacial charge carriers' recombination and the charge transport resistance, is presented. Due to the strong built-in potential and the internal driving electric-field, an ultra-high On/Off current ratio of 10⁶ with a responsivity of 86 mA W^-1 and a specific detectivity of 6.2 × 10¹¹ Jones was obtained at zero bias under 85 µW cm^-2 405 nm illumination and its rise/decay time at zero bias is 0.3/0.25 s. Therefore, the enhanced device performance strongly suggests the great potential of such a trilayer heterojunction device for use in high-performance perovskite photodetectors.

Large-area transparent flexible guanidinium incorporated MAPbI3 microstructures for high-performance photodetectors with enhanced stability

Unveiling the transparency and flexibility in perovskite-based photodetectors with superior photoresponse and environmental stability remains an open challenge. Here we report on guanidinium incorporated metal halide perovskite (MA_1-xGua_xPbI₃, x = 0 to 0.65) random percolative microstructure (RPM) fabrication using an ultra-fast spray coating technique. Remarkably, RPMs over a large area of 5 × 5 cm² on flexible substrates with a transparency of ∼50% can be achieved with enriched environmental stability. Transparent photodetectors based on MA_1-xGua_xPbI₃ (x = 0.12) RPMs manifest excellent performance with a responsivity of 187 A W^-1, a detectivity of 2.23 × 10¹² Jones and an external quantum efficiency of 44 115%. Additionally, the photodetectors exhibited superior mechanical flexibility under a wide range of bending angles and large number of binding cycles. Integrating features including transparency, high performance, stability, flexibility and scalability within a photodetector is unmatched and holds potential for novel applications in transparent and wearable optoelectronic devices.

Tailored Amphiphilic Molecular Mitigators for Stable Perovskite Solar Cells with 23.5% Efficiency

Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4-tert-butyl-benzylammonium iodide (tBBAI), is introduced, whose bulky tert-butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro-OMeTAD hole-transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation-less carrier recombination. The tert-butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full-sun illumination under maximum-power-point tracking under continuous simulated solar irradiation.

Toward High-Performance Electron/Hole-Transporting-Layer-Free, Self-Powered CsPbIBr2 Photodetectors via Interfacial Engineering

Self-powered photodetectors (PDs) with inorganic lead halide perovskites hold multiple traits of high sensitivity, fast response, independence from external power supply, and excellent sustainability and stability, thus holding a great promise for practical applications. However, they generally contain high-temperature-processed electron-transporting layers (ETLs) and high-cost, unstable hole-transporting layers (HTLs) coupled with noble metal electrodes, which bring significant obstacles of production cost and stability for their potential commercialization. Herein, we demonstrate the building of high-performance HTL/ETL-free, self-powered CsPbIBr₂ PD with simplified architecture of fluorine-doped tin oxide (FTO)/CsPbIBr₂/carbon upon interfacial modification by polyethyleneimine (PEI). The optimized PD yields a dark current of 2.03 × 10^-9 A, peak responsivity (R) of 0.32 A/W, maximum specific detectivity (D*) of 3.74 × 10¹² Jones, and response time of 1.21 μs. These figures of merit are far beyond those of the one prepared without PEI modification and even the PD containing TiO₂ ETL. Hence, our work suggests a highly feasible route to develop self-powered PDs with significantly simplified fabrication and a reduced production cost.

Optimizing the Performance of CsPbI3-Based Perovskite Solar Cells via Doping a ZnO Electron Transport Layer Coupled with Interface Engineering

Interface engineering has been regarded as an effective and noninvasive means to optimize the performance of perovskite solar cells (PSCs). Here, doping engineering of a ZnO electron transport layer (ETL) and CsPbI3/ZnO interface engineering via introduction of an interfacial layer are employed to improve the performances of CsPbI3-based PSCs. The results show that when introducing a TiO2 buffer layer while increasing the ZnO layer doping concentration, the open-circuit voltage, power conversion efficiency, and fill factor of the CsPbI3-based PSCs can be improved to 1.31 V, 21.06%, and 74.07%, respectively, which are superior to those of PSCs only modified by the TiO2 buffer layer or high-concentration doping of ZnO layer. On the one hand, the buffer layer relieves the band bending and structural disorder of CsPbI3. On the other hand, the increased doping concentration of the ZnO layer improves the conductivity of the TiO2/ZnO bilayer ETL because of the strong interaction between the TiO2 and ZnO layers. However, such phenomena are not observed for those of a PCBM/ZnO bilayer ETL because of the weak interlayer interaction of the PCBM/ZnO interface. These results provide a comprehensive understanding of the CsPbI3/ZnO interface and suggest a guideline to design high-performance PSCs.

A "Cocktail" Approach to Effective Surface Passivation of Multiple Surface Defects of Metal Halide Perovskites Using a Combination of Ligands

Surface passivation of metal halide perovskites (MHPs) is essential for their stability and various properties as well as functionalities, including optical and electronic. Passivation is important for both stabilizing intrinsic defects and preventing extrinsic damaging species from reaching the perovskite (PVK), such as water and oxygen. Because of the ternary nature of their chemical composition, multiple surface defects exist for both bulk and nanostructured PVKs, with the latter particularly prominent because of their extremely large surface-to-volume ratio. To effectively passivate the different surface defects, a multitude of different ligands are necessary because each type of defect likely requires a different ligand for optimal passivation, as has been successfully demonstrated in a number of systems in essentially a "cocktail" approach. Characteristics of the ligands that affect effectiveness of passivation include size, shape, charge and charge distribution, orientation, conductivity, and interligand interaction. Examples of ligands for MHPs include both cationic and anionic or zwitterionic species with varied valences. The challenge is to identify the most effective ligand for each type of defect, and addressing this will require further experimental and theoretical study.