Aspartate all-in-one doping strategy enables efficient all-perovskite tandems.

All-perovskite tandem solar cells hold great promise in surpassing the Shockley-Queisser limit for single-junction solar cells1-3. However, the practical use of these cells is currently hampered by the subpar performance and stability issues associated with mixed tin-lead (Sn-Pb) narrow-bandgap perovskite subcells in all-perovskite tandems4-7. In this study, we focus on the narrow-bandgap subcells and develop an all-in-one doping strategy for them. We introduce aspartate hydrochloride (AspCl) into both the bottom poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) and bulk perovskite layers, followed by another AspCl posttreatment. We show that a single AspCl additive can effectively passivate defects, reduce Sn4+ impurities and shift the Fermi energy level. Additionally, the strong molecular bonding of AspCl-Sn/Pb iodide and AspCl-AspCl can strengthen the structure and thereby improve the stability of Sn-Pb perovskites. Ultimately, the implementation of AspCl doping in Sn-Pb perovskite solar cells yielded power conversion efficiencies of 22.46% for single-junction cells and 27.84% (27.62% stabilized and 27.34% certified) for tandems with 95% retention after being stored in an N2-filled glovebox for 2,000 h. These results suggest that all-in-one AspCl doping is a favourable strategy for enhancing the efficiency and stability of single-junction Sn-Pb perovskite solar cells and their tandems.

Suppressing Phase Segregation in Wide Bandgap Perovskites for Monolithic Perovskite/Organic Tandem Solar Cells with Reduced Voltage Loss.

Wide bandgap (WBG) perovskites through tuning iodine/bromine ratios are capable of merging with narrow bandgap organic bulk heterojunctions to construct tandem solar cells to overcome the Shockley-Queisser limitation. However, WBG perovskites readily suffer from light-induced halide ion migration, leading to detrimental phase segregation and hence severe open-circuit voltage (VOC ) loss. Here, to solve this issue, lead thiocyanate (Pb(SCN)2 ) and 2-thiopheneethylammonium chloride (TEACl) are synergistically employed to passivate and stabilize WBG perovskites with 1.79 eV bandgap. It is demonstrated that the synergetic employment of Pb(SCN)2 and TEACl suppresses light-induced phase segregation, passivates WBG perovskite defects, and reduces non-radiative recombination, hence alleviating VOC loss. As a result, optimized WBG perovskite solar cells (PSCs) are obtained with an impressive VOC of 1.26 V and power conversion efficiency (PCE) over 17.0%. Furthermore, the interconnection layer is optimized to minimize the VOC loss and construct two-terminal perovskite/organic tandem solar cells with a narrow bandgap organic blend bulk heterojunction of PM6:Y6 and achieve a champion PCE of 22.29% with a high VOC of 2.072 V. In addition, these tandem solar cells maintain 81% of their initial efficiency after 1000 h continuous tracking at the maximum power point (MPP) under 100 mW cm-2 white light illumination.

Enhancing performance of perovskite solar cells with efficiency exceeding 21% via a graded-index mesoporous aluminum oxide antireflection coating.

Antireflection (AR) film is a widely used technology to enhance the performance of photovoltaic devices that require transparent electrodes in the photovoltaic industry. At present, several AR films including monolayer MgF2 or multilayered composite films, textured polydimethylsiloxane (PDMS) and porous SiO2 have been successfully applied due to their excellent properties. Nevertheless, all of the above-mentioned AR films have some minor drawbacks to overcome, for instance, the cost or thermal durability. Herein, we report a cost-effective and low-temperature method to fabricate a mesoporous aluminum oxide (meso-Al2O3) layer as the AR coating with high thermal durability, which will meet the fabrication condition of various photovoltaic devices. Briefly, the process begins at magnetron sputtering a compact Al2O3 film, which shows no AR effect, followed by a hot water treatment at 80 °C to turn the compact film into a mesoporous film with graded-index and AR effect. The application of meso-Al2O3 AR film enhances the maximum transmittance of our laboratory-used fluorine-doped tin oxide (FTO) from 84% to 89%, which is in good agreement with our theoretical simulation named graded-index approximation. Taking perovskite solar cells (PSCs) as an example, planar PSCs with meso-Al2O3 AR film deliver excellent photon conversion efficiency of 21.5%, which is higher than that of cells without meso-Al2O3 AR film (20.9%).

Space-Confined Growth of Individual Wide Bandgap Single Crystal CsPbCl3 Microplatelet for Near-Ultraviolet Photodetection.

Perovskite photodetectors (PDs) with tunable detection wavelength have attracted extensive attention due to the potential application in the field of imaging, machine vision, and artificial intelligence. Most of the perovskite PDs focus on I- or Br-based materials due to their easy preparation techniques. However, their main photodetection capacity is situated in the visible region because of their narrower bandgap. Cl-based wide bandgap perovskites, such as CsPbCl3 , are scarcely reported because of the bad film quality of the spin-coated Cl-based perovskite, due to the poor solubility of the precursor. Therefore, ultraviolet detection using high-quality full inorganic perovskite films, especially with high thermal stability of materials and devices, is still a big challenge. In this work, high-quality single crystal CsPbCl3 microplatelets (MPs) synthesized by a simple space-confined growth method at low temperature for near-ultraviolet (NUV) PDs are reported. The single CsPbCl3 MP PDs demonstrate a decent response to NUV light with a high on/off ratio of 5.6 × 103 and a responsivity of 0.45 A W-1 at 5 V. In addition, the dark current is as low as pA level, leading to detectivity up to 1011 Jones. Moreover, PDs possess good stability and repeatability.

A 3D self-supported coralline-like CuCo2S4@NiCo2S4 core-shell nanostructure composite for high-performance solid-state asymmetrical supercapacitors.

Rational construction of three dimensional (3D) composite structure is an important method to flexible supercapacitor electrodes and has been extensively developed. In this work, a 3D self-supported CuCo2S4@NiCo2S4 core-shell nanostructure grown on Nickel (Ni) foam, constructed by a hydrothermal method, was used as a novel supercapacitor electrode material. The unique structure possesses a large, specific surface area, rapid diffusion of electrolyte ions by numerous channels and avoids the use of additives and adhesives. The high electrical conductivity of the CuCo2S4 nanoneedle arrays can speed up electronic transmission. At a current density of 1 A g-1, the electrode material exhibits a high specific capacity of 539.2 C g-1 and cycling stability with 100% capacity retention after 5000 cycles in 3 M KOH. Furthermore, when the obtained CuCo2S4@NiCo2S4 was used as the positive electrode and an activated carbon was used as the negative electrode, a solid-state asymmetric supercapacitor was assembled. More importantly, the obtained solid-state asymmetric supercapacitor demonstrated excellent electrochemical performance. When the power density was 400 W kg-1, it delivered a high density of 23.4 W h kg-1 with a high voltage window of 1.6 V, thus demonstrating that the material has the potential for use as an efficient electrode for electrochemical capacitors. Due to its comprehensive electrochemical performance, the CuCo2S4@NiCo2S4 solid-state asymmetric supercapacitor effectively operated a red LED.

Aldehyde reduced Co3O4 to form oxygen vacancy and enhance the electrochemical performance for oxygen evolution reaction and supercapacitors.

Oxygen vacancy is a feasible approach to boost the electrochemical properties for metal oxides. In this work, a Co3O4 with abundant oxygen vacancy is synthesized via aldehyde reduction. After the procedure, the reduced Co3O4 exhibits larger electrochemical active surface areas and better electrical conductivity. These outstanding characteristics can improve its performance of catalytic and energy storage. As for catalyst of oxygen evolution reaction, the reduced Co3O4 delivers a smaller potential of 1.55 V versus the reversible hydrogen electrode to realize a current density of 10 mA cm-2 and a lower Tafel slope of 71 mV dec-1 in alkaline solution, and these values are smaller than those of pristine Co3O4. Especially the reduced Co3O4 possesses superior stability: the measurements of the polarization curves before and after 15h of stability tests basically coincide. In a supercapacitor, the positive electrode of reduced Co3O4 achieves about 1.7 times areal capacitance of pristine Co3O4 at current density of 1 mA cm-2. Significantly, the superior cycling stability is still retained. Also, an aqueous asymmetric supercapacitor is assembled to evaluate the energy storage performance of the R-Co3O4. Moreover, the oxygen vacancy formation strategy for Co3O4 may be generally extended to other metal oxides for application in energy storage and conversion.

Rational Construction of Hollow Core-Branch CoSe2 Nanoarrays for High-Performance Asymmetric Supercapacitor and Efficient Oxygen Evolution.

Metal selenides have great potential for electrochemical energy storage, but are relatively scarce investigated. Herein, a novel hollow core-branch CoSe2 nanoarray on carbon cloth is designed by a facile selenization reaction of predesigned CoO nanocones. And the electrochemical reaction mechanism of CoSe2 in supercapacitor is studied in detail for the first time. Compared with CoO, the hollow core-branch CoSe2 has both larger specific surface area and higher electrical conductivity. When tested as a supercapacitor positive electrode, the CoSe2 delivers a high specific capacitance of 759.5 F g-1 at 1 mA cm-2 , which is much larger than that of CoO nanocones (319.5 F g-1 ). In addition, the CoSe2 electrode exhibits excellent cycling stability in that a capacitance retention of 94.5% can be maintained after 5000 charge-discharge cycles at 5 mA cm-2 . An asymmetric supercapacitor using the CoSe2 as cathode and an N-doped carbon nanowall as anode is further assembled, which show a high energy density of 32.2 Wh kg-1 at a power density of 1914.7 W kg-1 , and maintains 24.9 Wh kg-1 when power density increased to 7354.8 W kg-1 . Moreover, the CoSe2 electrode also exhibits better oxygen evolution reaction activity than that of CoO.

Bifunctional bamboo-like CoSe2 arrays for high-performance asymmetric supercapacitor and electrocatalytic oxygen evolution.

Bifunctional bamboo-like CoSe2 arrays are synthesized by thermal annealing of Co(CO3)0.5OH grown on carbon cloth in Se atmosphere. The CoSe2 arrays obtained have excellent electrical conductivity, larger electrochemical active surface areas, and can directly serve as a binder-free electrode for supercapacitors and the oxygen evolution reaction (OER). When tested as a supercapacitor electrode, the CoSe2 delivers a higher specific capacitance (544.6 F g-1 at current density of 1 mA cm-2) compared with CoO (308.2 F g-1) or Co3O4 (201.4 F g-1). In addition, the CoSe2 electrode possesses excellent cycling stability. An asymmetric supercapacitor (ASC) is also assembled based on bamboo-like CoSe2 as a positive electrode and active carbon as a negative electrode in a 3.0 M KOH aqueous electrolyte. Owing to the unique stucture and good electrochemical performance of bamboo-like CoSe2, the as-assembled ACS can achieve a maximum operating voltage window of 1.7 V, a high energy density of 20.2 Wh kg-1 at a power density of 144.1 W kg-1, and an outstanding cyclic stability. As the catalyst for the OER, the CoSe2 exhibits a lower potential of 1.55 V (versus RHE) at current density of 10 mA cm-2, a smaller Tafel slope of 62.5 mV dec-1 and an also outstanding stability.

A comparative study on top-gated and bottom-gated multilayer MoS2 transistors with gate stacked dielectric of Al2O3/HfO2.

Top-gated and bottom-gated transistors with multilayer MoS2 channel fully encapsulated by stacked Al2O3/HfO2 (9 nm/6 nm) were fabricated and comparatively studied. Excellent electrical properties are demonstrated for the TG transistors with high on-off current ratio of 108, high field-effect mobility of 102 cm2 V-1 s-1, and low subthreshold swing of 93 mV dec-1. Also, enhanced reliability has been achieved for the TG transistors with threshold voltage shift of 10-3-10-2 V MV-1 cm-1 after 6 MV cm-1 gate-biased stressing. All improvement for the TG device can be ascribed to the formed device structure and dielectric environment. Degradation of the performance for the BG transistors should be attributed to reduced gate capacitance density and deteriorated interface properties related to vdW gap with a thickness about 0.4 nm. So, the TG transistor with MoS2 channel fully encapsulated by stacked Al2O3/HfO2 is a promising way to fabricate high-performance ML MoS2 field-effect transistors for practical electron device applications.

Reducing Hysteresis and Enhancing Performance of Perovskite Solar Cells Using Low-Temperature Processed Y-Doped SnO2 Nanosheets as Electron Selective Layers.

Despite the rapid increase of efficiency, perovskite solar cells (PSCs) still face some challenges, one of which is the current-voltage hysteresis. Herein, it is reported that yttrium-doped tin dioxide (Y-SnO2 ) electron selective layer (ESL) synthesized by an in situ hydrothermal growth process at 95 °C can significantly reduce the hysteresis and improve the performance of PSCs. Comparison studies reveal two main effects of Y doping of SnO2 ESLs: (1) it promotes the formation of well-aligned and more homogeneous distribution of SnO2 nanosheet arrays (NSAs), which allows better perovskite infiltration, better contacts of perovskite with SnO2 nanosheets, and improves electron transfer from perovskite to ESL; (2) it enlarges the band gap and upshifts the band energy levels, resulting in better energy level alignment with perovskite and reduced charge recombination at NSA/perovskite interfaces. As a result, PSCs using Y-SnO2 NSA ESLs exhibit much less hysteresis and better performance compared with the cells using pristine SnO2 NSA ESLs. The champion cell using Y-SnO2 NSA ESL achieves a photovoltaic conversion efficiency of 17.29% (16.97%) when measured under reverse (forward) voltage scanning and a steady-state efficiency of 16.25%. The results suggest that low-temperature hydrothermal-synthesized Y-SnO2 NSA is a promising ESL for fabricating efficient and hysteresis-less PSC.

In situ grown Ni9S8 nanorod/O-MoS2 nanosheet nanocomposite on carbon cloth as a free binder supercapacitor electrode and hydrogen evolution catalyst.

Transition metal sulfide nanostructure composites have received significant attention as energy conversion and storage devices. In this work, we report a three-dimension (3D) nanostructure with the Ni9S8 nanorods embedded in oxygen-incorporated MoS2 (O-MoS2) nanosheets for supercapacitors and hydrogen evolution catalysts. The in situ grown Ni9S8/O-MoS2 nanocomposite on carbon cloth can be used as a free binder supercapacitor electrode and hydrogen evolution catalyst. The Ni9S8/O-MoS2 nanocomposite exhibits electrochemical behaviors with a specific capacitance of 907 F g-1 (at 2 A g-1) and good cycle stability after 1200 cycles due to its unique mutual embedding 3D nanostructure. Furthermore, the Ni9S8/O-MoS2 nanocomposite also shows highly electrocatalytic features for hydrogen production with an onset overpotential of ∼150 mV and a low Tafel slope of ∼81 mV dec-1. The oxygen incorporation of MoS2 provides more active sites to participate in the catalytic process for the hydrogen evolution reaction.

TiO2-ZnS Cascade Electron Transport Layer for Efficient Formamidinium Tin Iodide Perovskite Solar Cells.

Achieving high open-circuit voltage (Voc) for tin-based perovskite solar cells is challenging. Here, we demonstrate that a ZnS interfacial layer can improve the Voc and photovoltaic performance of formamidinium tin iodide (FASnI3) perovskite solar cells. The TiO2-ZnS electron transporting layer (ETL) with cascade conduction band structure can effectively reduce the interfacial charge recombination and facilitate electron transfer. Our best-performing FASnI3 perovskite solar cell using the cascaded TiO2-ZnS ETL has achieved a power conversion efficiency of 5.27%, with a higher Voc of 0.380 V, a short-circuit current density of 23.09 mA cm-2, and a fill factor of 60.01%. The cascade structure is further validated with a TiO2-CdS ETL. Our results suggest a new approach for further improving the performance of tin-based perovskite solar cells with a higher Voc.

In situ synthesis of 3D CoS nanoflake/Ni(OH)2 nanosheet nanocomposite structure as a candidate supercapacitor electrode.

A three-dimensional (3D) CoS/Ni(OH)2 nanocomposite structure based on CoS nanoflakes and two-dimensional (2D) Ni(OH)2 nanosheets were in situ synthesized on Ni foam by a whole hydrothermal reaction and electrodeposition process. The 3D CoS/Ni(OH)2 nanocomposite structures demonstrate the combined advantages of a sustained cycle stability of CoS and high specific capacitance from Ni(OH)2. The obtained CoS/Ni(OH)2 nanocomposite structures on Ni foam can directly serve as a binder-free electrode for a supercapacitor. For the 3D CoS/Ni(OH)2 nanocomposite electrode, the high specific capacitance is 1837 F g(-1) at a scan rate of 1 mV s(-1), which is obviously higher than both the bare CoS electrode and Ni(OH)2 electrode. The galvanostatic charge and discharge measurements illustrate that the 3D CoS/Ni(OH)2 nanocomposite electrode possesses excellent cycle stability, and it keeps a 95.8% retention of the initial capacity after 5000 cycles. Electrochemical impedance spectroscopy measurements also confirm that the 3D CoS/Ni(OH)2 nanocomposite electrode has better electrochemical characteristics. These remarkable performances can be attributed to the unique 3D nanoporous structure of CoS/Ni(OH)2 which leads to a large accessible surface area and a high stability during long-term operation. In addition, 2D Ni(OH)2 nanosheets in 3D nanocomposite structures can afford rapid mass transport and a strong synergistic effect of CoS and Ni(OH)2 as individual compositions contribute to the high performance of the nanocomposite structure electrode. These results may promote the design and implementation of nanocomposite structures in advanced supercapacitors.

Efficient planar Sb2S3 solar cells using a low-temperature solution-processed tin oxide electron conductor.

Efficient planar antimony sulfide (Sb2S3) heterojunction solar cells have been made using chemical bath deposited (CBD) Sb2S3 as the absorber, low-temperature solution-processed tin oxide (SnO2) as the electron conductor and poly (3-hexylthiophene) (P3HT) as the hole conductor. A solar conversion efficiency of 2.8% was obtained at 1 sun illumination using a planar device consisting of F-doped SnO2 substrate/SnO2/CBD-Sb2S3/P3HT/Au, whereas the solar cells based on a titanium dioxide (TiO2) electron conductor exhibited a power conversion efficiency of 1.9%. Compared with conventional Sb2S3 sensitized solar cells, the high-temperature processed mesoscopic TiO2 scaffold is no longer needed. More importantly, a low-temperature solution-processed SnO2 layer was introduced for electron transportation to substitute the high-temperature sintered dense blocking TiO2 layer. Our planar solar cells not only have simple geometry with fewer steps to fabricate but also show enhanced performance. The higher efficiency of planar Sb2S3 solar cell devices based on a SnO2 electron conductor is attributed to their high transparency, uniform surface, efficient electron transport properties of SnO2, suitable energy band alignment, and reduced recombination at the interface of SnO2/Sb2S3.

Low-temperature solution-processed tin oxide as an alternative electron transporting layer for efficient perovskite solar cells.

Lead halide perovskite solar cells with the high efficiencies typically use high-temperature processed TiO2 as the electron transporting layers (ETLs). Here, we demonstrate that low-temperature solution-processed nanocrystalline SnO2 can be an excellent alternative ETL material for efficient perovskite solar cells. Our best-performing planar cell using such a SnO2 ETL has achieved an average efficiency of 16.02%, obtained from efficiencies measured from both reverse and forward voltage scans. The outstanding performance of SnO2 ETLs is attributed to the excellent properties of nanocrystalline SnO2 films, such as good antireflection, suitable band edge positions, and high electron mobility. The simple low-temperature process is compatible with the roll-to-roll manufacturing of low-cost perovskite solar cells on flexible substrates.

Enhanced field emission from in situ synthesized 2D copper sulfide nanoflakes at low temperature by using a novel controllable solvothermal preferred edge growth route.

A facile one-pot solvothermal route using the reaction of sputtered copper film and sulfur powder in ethanol solution at a low temperature of 90 °C for 12 hours has been implemented to in situ synthesize 2D hexagonal copper sulfide (CuS) nanoflakes. Their field electron emission (FE) characteristics were investigated and were found to have a close relationship with the copper film's thickness. The lowest turn on electric field (Eon) was 2.05 V µm(-1) and the largest field enhancement factor (ß) was 7261 when the copper film's thickness was 160 nm. Furthermore, through a preferred edge growth route, patterned CuS nanoflakes were synthesized with the combined effect from a copper film seed layer and a passivation layer to further improve FE properties with an Eon of 1.65 V µm(-1) and a ß of 8351. The mechanism of the patterned CuS nanoflake preferred edge growth is reported and discussed for the first time.

Enhanced electroluminescence using Ta2O5/ZnO/HfO2 asymmetric double heterostructure in ZnO/GaN-based light emitting diodes.

ZnO/GaN-based light-emitting diodes (LEDs) with improved asymmetric double heterostructure of Ta2O5/ZnO/HfO2 have been fabricated. Electroluminescence (EL) performance has been enhanced by the HfO2 electron blocking layer and further improved by continuing inserting the Ta2O5 hole blocking layer. The origins of the emission have been identified, which indicated that the Ta2O5/ZnO/HfO2 asymmetric structure could more effectively confine carriers in the active i-ZnO layer and meanwhile suppresses of radiation from GaN. This device exhibits superior stability in long-time running. It's hoped that the asymmetric double heterostructure may be helpful for the development of the future ZnO-based LEDs.

Unusual electroluminescence from n-ZnO@i-MgO core-shell nanowire color-tunable light-emitting diode at reverse bias.

Light-emitting diodes (LEDs) based on n-ZnO@i-MgO core-shell (CS) nanowires (NWs) are herein demonstrated and characterized. MgO insulating layers were rationally introduced as shells to modify/passivate the surface defects of ZnO NWs. A high-quality ZnO/MgO interface was attained and the optically pumped near-band-edge emission of the bare ZnO NWs was greatly enhanced after cladding i-MgO shells. Electroluminescence (EL) spectra measured in the whole UV-visible range revealed that light emission can only be detected when LEDs were applied with reverse bias. Moreover, the emission color can be tuned from orange to bright white with increasing reverse bias. We explored these interesting results tentatively in terms of the energy-band diagram of the heterojunction and it was found that the interfacial i-MgO shells not only acted as an insulator to prevent a short circuit between the two electrodes, but also offered a potential energy difference so that electron tunneling was energetically possible, both of which were essential to generate the reverse-bias EL. The dipole-forbidden d-d transitions by the Laporte selection rule in the p-NiO might be the reason to why there is no light being detected from the CS NW LED under forward bias. It is hoped that this simple and facile route may provide an effective approach in designing low-cost CS NW LEDs.

Micro/Nano Perovskite Materials for Advanced X-ray Detection and Imaging.

Halide perovskites have emerged as highly promising materials for ionizing radiation detection due to their exceptional characteristics, including a large mobility-lifetime product, strong stopping power, tunable band gap, and cost-effective crystal growth via solution processes. Semiconductor-type X-ray detectors employing various micro/nano perovskite materials have shown impressive progress in achieving heightened sensitivity and lower detection limits. Here, we present a comprehensive review of the applications of micro/nano perovskite materials for direct type X-ray detection, with a focus on the requirements for micro/nano crystal assembly and device properties in advanced X-ray detectors. We explore diverse processing techniques and optoelectronic considerations applied to perovskite X-ray detectors. Additionally, this review highlights the challenges and promising opportunities for perovskite X-ray detector arrays in real-world applications, potentially necessitating further research efforts.

Tailoring Perovskite Surface Potential and Chelation Advances Efficient Solar Cells.

Modifying perovskite surface using various organic ammonium halide cations has proven to be an effective approach for enhancing the overall performance of perovskite solar cells. Nevertheless, the impact of the structural symmetry of these ammonium halide cations on perovskite interface termination has remained uncertain. Here, this work investigates the influence of symmetry on the performance of the devices, using molecules based on symmetrical bis(2-chloroethyl)ammonium cation (B(CE)A+) and asymmetrical 2-chloroethylammonium cation (CEA+) as interface layers between the perovskite and hole transport layer. These results reveal that the symmetrical B(CE)A+ cations lead to a more homogeneous surface potential and more comprehensive chelation with uncoordinated Pb2+ compared to the asymmetrical cations, resulting in a more favorable energy band alignment and strengthened defect healing. This strategy, leveraging the spatial geometrical symmetry of the interface cations, promotes hole carrier extraction between functional layers and reduces nonradiative recombination on the perovskite surface. Consequently, perovskite solar cells processed with the symmetrical B(CE)A+ cations achieve a power conversion efficiency (PCE) of 25.60% and retain ≈91% of their initial PCE after 500 h of maximum power point operation. This work highlights the significant benefits of utilizing structurally symmetrical cations in promoting the performance and stability of perovskite solar cells.