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Two-dimensional (2D) organic–inorganic hybrid metal halide perovskites (MHPs) are promising as semiconducting light-emitting materials due to improved environmental stability and unique optical properties, compared with three-dimensional MHPs. However, toxic Pb and relatively low photoluminescence quantum yield (PLQY) limit the potentials of these 2D lead halides in solid-state lighting. Herein, we report a series of F-doped, 2D zinc halide-layered perovskites based on phenylethylamine (PEA), PEA2ZnFxCl4–x, which exhibits efficient white light and the highest PLQY of 21.02% at x = 0.40, seven times higher than that of non-F doping samples for 2D hybrid white-light-emitting MHPs. Steady-state and temperature-dependent optical measurements verify that the white-emission arose from self-trapped excitons and highlight the significant effects of F-doping and defect passivation on efficient photoluminescence. Especially, F-doped 2D zinc halide perovskites show ultrahigh stability with negligible degradation for 1000 h at 80 °C. This work paves an avenue to designing efficient and stable single-component white-light-emitting diodes in solid-state lighting. [ABSTRACT FROM AUTHOR]

Inthis study, phosphotungstic acid immobilized on amine-graftedgraphene oxide (GOAP) was prepared successfully by silylanizationand electrostatic interaction. The obtained GOAP was characterizedby Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersivespectroscopy (EDS), high-resolution transmission electron microscopy(HRTEM), zeta potential measurements, and X-ray photoelectron spectroscopy(XPS). Systematic studies demonstrated that GOAP had excellent catalyticactivities and robustness in the one-pot tandem deacetalization–nitroaldolreaction. The key role of the acid/base ratio in the catalytic performanceof this bifunctional catalyst was also revealed by preliminary kineticstudies. This bifunctional catalyst might find promising applicationsin green chemistry, as it can not only reduce costs and waste by savingseparation/purification steps and solvents/reagents, but also increasethe yield by avoiding the separation of intermediate products. [ABSTRACT FROM AUTHOR]

The two-step sequential deposition strategy has garnered widespread usage in the fabrication of high-performance perovskite solar cells based on FAPbI 3 . However, the rapid reaction between FAI and PbI 2 during preparation often leads to incomplete reactions, reducing the device efficiency and stability. Herein, we introduced a multifunctional additive, 2-thiophenyl trifluoroacetone (TTA), into the FAI precursor. The incorporation of TTA has proven to be highly effective in slowing the reaction rate between FAI and PbI 2 , resulting in increased perovskite formation and improved efficiency and stability of the devices. TTA's CF 3 groups interact with FAI via hydrogen bonding, effectively suppressing FA + defects. The S and C═O groups share lone pair electrons with uncoordinated Pb 2+ , leading to a reduction in perovskite film defects and suppressing nonradiative recombination. Additionally, the CF 3 groups impart hydrophobicity, protecting the perovskite film from moisture-induced erosion. As a result, the TTA-modified perovskite film achieves a Champion efficiency of 23.42% compared to the control's 21.52, with 20.58% efficiency for a 25 cm 2 solar module. Remarkably, the unencapsulated Champion device retains 86% of its initial PCE after 1080 h under dark conditions (60 ± 5 °C, 35 ± 5% RH), indicating enhanced long-term stability. These findings offer a promising and cost-effective tactic for high-quality perovskite film fabrication.

Recent investigations reveal elemental semimetal (Bi and Sb) contacts fabricated with conventional deposition processes exhibit a remarkable capacity of approaching the quantum limit in two-dimensional (2D) semiconductor contacts, implying it might be an optimal option to solve the contact issue of 2D semiconductor electronics. Here, we demonstrate novel compound Dirac semimetal ZrTe 2 contacts to MoS 2 constructed by a nondestructive van der Waals (vdW) transfer process, exhibiting excellent ohmic contact characteristics with a negligible Schottky barrier. The band hybridization between ZrTe 2 and MoS 2 was verified. The bilayer MoS 2 transistor with a 250 nm channel length on a 20 nm thick hexagonal boron nitride (h-BN) exhibits an I ON / I OFF current ratio over 10 5 and an on-state current of 259 μA μm -1 . The current results reveal that 2D compound semimetals with vdW contacts can offer a diverse selection of proper semimetals with adjustable work functions for the next-generation 2D-based beyond-silicon electronics.

The fabrication of α-FAPbI 3 perovskite films usually requires high temperature annealing above 150 °C, and the residual tensile strain in the films seriously affects the stability of α-FAPbI 3 by converting to δ-phase FAPbI 3 . Here, we use MASCN surface treatment of FAPbI 3 films to induce a rotation of the coplanar octahedron [PbI 6 ] 4- to the metric octahedron for the strong interaction of SCN - with Pb 2+ , converting δ-FAPbI 3 into α-FAPbI 3 highly crystalline films at room temperature. The optimized FAPbI 3 films have high stability due to releasing residual tensile strains after MASCN treatment. The efficiency of the MASCN-treated unannealed FAPbI 3 PSC is 19.03%, while the optimized FAPbI 3 annealed at 100 °C shows a maximum PCE of 21.95% on a small area. The solar cell stability for humidity, light, and thermal stability are significantly improved. The MASCN treated FAPbI 3 achieves a PCE of 15.32% on a PSC module with an effective area of 9.6 cm 2 and maintains an initial efficiency of 94.1% after 100 days of ageing at 85 °C and 85% humidity.

Magnetic tunnel junctions (MTJs) based on van der Waals (vdW) heterostructures with sharp and clean interfaces on the atomic scale are essential for the application of next-generation spintronics. However, the lack of room-temperature intrinsic ferromagnetic crystals with perpendicular magnetic anisotropy has greatly hindered the development of vertical MTJs. The discovery of room-temperature intrinsic ferromagnetic two-dimensional (2D) crystal Fe 3 GaTe 2 has solved the problem and greatly facilitated the realization of practical spintronic devices. Here, we demonstrate a room-temperature MTJ based on a Fe 3 GaTe 2 /WS 2 /Fe 3 GaTe 2 heterostructure for the first time. The tunneling magnetoresistance (TMR) ratio is up to 213% with a high spin polarization of 72% at 10 K, the highest ever reported in Fe 3 GaTe 2 -based MTJs up to now. A tunneling spin-valve signal robustly persists at room temperature (300 K) with a bias current down to 10 nA. Moreover, the spin polarization can be modulated by bias current and the TMR shows a sign reversal at a large bias current. Our work sheds light on the potential application of low-energy consumption in all-2D vdW spintronics and offers alternative routes for the electronic control of spintronic devices.

SnO 2 is widely used as the electron transport layer (ETL) in n-i-p perovskite solar cells. However, the deep-level defects at the interface between SnO 2 and the perovskite film will lead to energy loss, reducing the open-circuit voltage. Therefore, the interface optimization is essential to raise the efficiency and enhance the stability of perovskite solar cells. In this work, we introduce NH 4 F into the SnO 2 electron transport layers, and the optimized SnO 2 films reduce the interface defect density, improve the charge extraction, and reveal a better energy-level arrangement. Compared to the conventional SnO 2 perovskite solar cell, the average V oc is improved by 70 mV with the champion efficiency up to 22.12%. Moreover, the unencapsulated F-doped SnO 2 perovskite solar cells show better thermal stability (maintained 86.2%) and humidity stability (maintained 80.8%) after 35 days.

The intrinsically nonmagnetic feature of van der Waals (vdW) layered transition-metal dichalcogenide (TMDC) semiconductors limits the spintronic applications of these semiconductors. In this paper, we demonstrate a facile Te flux strategy to induce intrinsic ferromagnetism in the vdW layered 2H-MoTe 2 semiconductor by magnetic chromium (Cr) doping. The Curie temperature ( T c ) and saturation magnetization ( M s ) can be well tuned by adjusting the Cr doping concentration. A notable T c up to 275 K can be achieved for the vdW layered Cr-doped 2H-MoTe 2 bulk crystals, which is much higher than that of recently reported van der Waals ferromagnetic semiconductors ( T c is mostly less than 70 K), in contrast to the diamagnetic feature of the pristine MoTe 2 . Meanwhile, the highest M s of the vdW layered Cr-doped 2H-MoTe 2 bulk crystals can reach 4.78 emu g -1 , which is stronger than most values reported for magnetic-element-doped van der Waals materials. In addition, all of the as-grown semiconducting Cr-doped 2H-MoTe 2 (Cr-2H-MoTe 2 ) single crystals display a large magnetic anisotropy with an out-of-plane easy axis of magnetization. The observed ferromagnetism in the Cr-2H-MoTe 2 has intrinsic characteristics, which can be mainly attributed to the spin polarization caused by Cr doping as confirmed by the density functional theory (DFT) calculations. Our approach offers an avenue to tune the ferromagnetism in the vdW layered semiconductor and explore its diverse spintronic and magnetoelectric applications.

Passivation of electronic defects on the surface and at grain boundaries (GBs) of perovskite films has become one of the most effective tactics to suppress charge recombination in perovskite solar cells. It is demonstrated that trap states can be effectively passivated by Lewis acid or base functional groups. In this work, nicotinamide (NTM, commonly known as vitamin B3 or vitamin PP) serving as a Lewis base additive is introduced into the PbI 2 and/or FAI: MABr: MACl precursor solution to obtain NTM modified perovskite films. It has been found that the NTM in the perovskite film can well passivate surface and GBs defects, control the film morphology and enhance the crystallinity via its interaction with a lone pair of electrons in nitrogen. In the presence of the NTM additive, we obtained enlarged perovskite crystal grain about 3.6 μm and a champion planar perovskite solar cell with efficiency of 21.72% and negligible hysteresis. Our findings provide an effective route for crystal growth and defect passivation to bring further increases on both efficiency and stability of perovskite solar cells.

The inorganic CsPbI 2 Br perovskite faces serious challenges of low phase stability and high moisture sensitivity. The moisture controllable process of a hole-transporting layer (HTL) is crucial for the development of stable and efficient inorganic perovskite solar cells (IPSCs). In this work, we proposed an oxidization-free spiro-OMeTAD hole-transport layer (HTL) with a preoxidized spiro-OMeTAD solution to prevent moisture and completely avoid the phase transition of CsPbI 2 Br from the α-phase to β-phase. The oxidization-free HTL exhibited improved surface hydrophobic properties, smoother morphology, and optimized energy-level alignment compared with a traditional HTL. As a result, the CsPbI 2 Br-based IPSCs achieved an efficiency of up to 14.2 and 86.6% of the initial power conversion efficiency (PCE) with 2000 h storage. Meanwhile, this oxidization-free HTL was applied in CH 3 NH 3 PbI 3 -based PSCs and obtained 13.8% PCE enhancement, which proved the universality of the solution preoxidization tactic. We believe that the oxidization-free HTL could be an efficient strategy to replace traditional HTLs and can be widely used in perovskite solar cells, especially in moisture-sensitive PSCs.

The sluggish oxygen evolution reaction (OER) and costly noble-metal oxide catalysts hinder the vast usage of environmentally friendly water splitting for hydrogen production. Elemental doping by partial replacing of parent metal elements with elements of higher electronegativity is considered to be one of the most efficient strategies to promote the electrocatalytic OER performance. In this work, we synthesize an efficient hierarchical highly wrinkled NiFeCu phosphide nanosheet on nanodendrite Ni 3 S 2 /NiF substrates through partial replacement of Cu instead of Ni and Fe in NiFeP@Ni 3 S 2 /NiF by using a facile electrodeposition method. The NiFeCuP@Ni 3 S 2 /NiF electrocatalyst needs only 230, 282, and 351 mV to reach 10, 50, and 100 mA × cm -2 , respectively. Notably, this electrocatalyst shows one of the lowest OER overpotentials at 10 mA/cm -2 for metal phosphides and endured the OER at 20 mA × cm -2 for 18 h with negligible voltage elevation. The X-ray photoelectron spectroscopy (XPS), double-layer capacitance ( C dl ) plots, and electrochemical impedance spectroscopy show that the partial Cu doping in NiFeP@Ni 3 S 2 /NiF not only can change the electron density around Ni and Fe but also can increase the electrochemically active surface area and conductivity of electrocatalysts.

It is imperative to explore practical methods and materials to drive the development of high energy density lithium metal batteries. The constuciton of nanostructure electrodes and surface engineering on the current collectors are the two most effective strategies to regulate the homogeneous Li plating/stripping to relieve the Li dendrites and infinite volume change problems. Based on the low stacking fault energy of the Cu-Zn alloy, we present a novel chemical energy release induced surface atom diffusion strategy, which is achieved by the negative Gibbs free energy from the surface oxidation reaction and subsequent replacement reaction under thermal treatment in air, to realize a uniform upper ZnO nanoparticles coating. Furthermore, we apply the modified brass mesh as a lithiophilic current collector to decrease the Li deposition nucleation overpotential and effectively restrain the Li dendrite growth. The modified brass current collector achieves a long-term cycling stability of 500 cycles at 2.0 mA cm -2 . We have verified the effectiveness of our chemical energy release modification strategy on a 1 m 2 brass mesh and other Cu alloy (Tin bronze mesh), which demonstrates its great opportunities for scalable and safe lithium metal batteries.

Because of the disadvantages of commercial graphite anodes for high-power lithium-ion batteries, a kind of spinel nanolithium titanate (Li 4 Ti 5 O 12 )/graphene microsphere composite [denoted as LTO/reduced graphene oxide (rGO)] is successfully synthesized. The as-prepared composite is made up of curled graphene sheets which are anchored with nano-Li 4 Ti 5 O 12 particles. These nano-Li 4 Ti 5 O 12 particles are uniformly decorated on the conductive graphene framework and their sizes range from just 15 to 20 nm. In the as-prepared composite, the curled graphene sheets form a unique mesopore-oriented structure which provides plenty of three-dimensional channels for ion transportation. These structure characters greatly improve both the electron conductivity and Li + diffusion ability. The ratio of pseudocapacitive capacity dramatically increases in the obtained LTO/rGO composite and generates excellent ultrahigh rate performances. The as-prepared LTO/rGO composite delivers a reversible capacity of 70.3 mA h g -1 at 200 C and a capacity retention of 84.7% after 1000 cycles at 50 C. As the current density varies from 30 to 100 C, the special capacity remains unchanged (about 112 mA h g -1 ). These results show that the graphene framework-supported nano-Li 4 Ti 5 O 12 composite has potential application in high-power lithium-ion batteries.

Fullerene derivatives have been popularly applied as electron transport layers (ETLs) of inverted (p-i-n) planar heterojunction perovskite solar cells (iPSCs) due to their strong electron-accepting abilities, and so far, [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) has been the most commonly used ETL, which suffers, however, from high cost due to the complicated synthetic route. Herein, novel pyridine-functionalized fullerene derivatives (abbreviated as C 60 -Py) were synthesized facilely via a one-step 1,3-dipolar cycloaddition reaction and applied as ETLs superior to PCBM in iPSC devices. Three pyridine-functionalized fullerene derivatives with different alkyl groups, including methyl, n-butyl, and n-hexyl, grafted onto the pyrrolidine moiety (abbreviated as C 60 -MPy, C 60 -BPy, and C 60 -HPy, respectively) were synthesized. According to cyclic voltammogram study, the chain length of the N-alkyl group has negligible influence on the molecular energy level of C 60 -Py. However, the ETL performance of C 60 -Py is sensitively dependent on the chain length of the N-alkyl group, with C 60 -BPy exhibiting the highest power conversion efficiency (PCE) of 16.83%, which surpasses that based on PCBM ETL (15.87%). The PCE enhancement of C 60 -BPy device is attributed to the coordination interactions between the pyridine moiety with the Pb 2+ ion of CH 3 NH 3 PbI 3 perovskite, which anchor C 60 -BPy onto perovskite film and reinforce the passivation of the trap state within the CH 3 NH 3 PbI 3 perovskite film and suppress the nonradiative electron-hole recombinations, leading to enhanced electron transport reflected by the increase of short-circuit current density ( J sc ). The ambient stability of C 60 -HPy-based device is much better than that based on PCBM ETL since its long N-alkyl group can function as a superior encapsulating layer protecting the CH 3 NH 3 PbI 3 layer from contact with the ambient moisture.

Tungsten ditellurium (WTe 2 ) is one of most important layered transition metal dichalcogenides (TMDs) and exhibits various prominent physical properties. All the present methods for WTe 2 preparation need strict conditions such as high temperature or cannot be applied in large scale, which limits its practical applications. In addition, most studies on WTe 2 focus on its physical properties, whereas its electrochemical properties are still illusive with little investigation. Here, we develop a facile and scalable two-step method to synthesize high-quality WTe 2 nanoribbon crystals with 1T' Weyl semimetal phase for the first time. Highly crystalline 1T'-WTe 2 nanoribbons can be obtained on a large scale through this two-step method. In addition, the electrochemical tests show that WTe 2 nanoribbons exhibit smaller overpotential and much better hydrogen evolution reaction catalytic performance than other tungsten-based sulfide and selenide (WS 2 , WSe 2 ) nanoribbons of same morphology and under same preparation conditions. WTe 2 nanoribbons show a Tafel slope of 57 mV/dec, which is one of best values for TMD catalysts and about 2 and 4 times smaller than that for 2H-WS 2 nanoribbons (135 mV/dec) and 2H-WSe 2 nanoribbons (213 mV/dec), respectively. 1T'-WTe 2 nanoribbons also show ultrahigh stability in 5000 cycles and 20 h at 10 mA/cm 2 . The better performance is attributed to high conductivity of semimetallic 1T'-phase-stable WTe 2 nanoribbons with one or two order higher charge-transfer rate than normally semiconducting 2H-stable WS 2 and WSe 2 nanoribbons. These results open the door for electrochemical applications of Weyl semimetallic TMDs.

Sodium-ion batteries (SIBs) are expected to be a promising commercial alternative to lithium-ion batteries for grid electricity storage due to their potential low cost in the near future. Up to the present, the anode material still remains a great challenge for the application of SIBs, especially at room temperature. Graphite has an obvious limitation to store larger radius sodium ions (Na + ) in comparison with lithium ions (Li + ), while the hard carbon with large interlayer distance can demonstrate a relatively high storage capability and durable cycle life. However, the disadvantages of low initial Coulombic efficiency (ICE) mainly caused by large surface area and high cost synthetic approach hinder its practical applications. Herein, a new coupled carbonization strategy is presented to prepare a cost-effective hard carbon material by pyrolyzing and carbonizing the mixture of abundant sucrose and phenolic resin. Benefiting from the specialized pyrolysis reaction process and optimized conditions as studied in detail, the hard carbon has an extremely low surface area of 1.54 m 2 g -1 and high initial Coulombic efficiency of 87%, which have been rarely reported before and enhance the utilization efficiency of Na + consumption within the cathode in the future. More importantly, the hard carbon, with a high interlayer distance 3.95 Å, can deliver a higher capacity of 319 mAh g -1 and maintain a finer capacity retention of 90% over 150 cycles. Besides, a full cell with the configuration of as-prepared hard carbon anode versus an air-stable O3-Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ]O 2 cathode is further presented, and it has a high ICE of 80% and energy density of 256 Wh kg anode -1 (vs hard carbon) with reliable cycle performance. The results demonstrate that our synthetic strategy is feasible and extendable, while the tunable carbon-based materials should have wider applications in addition to the attractive properties in Na-ion batteries.

Arsenic-based feed additives, such as roxarsone (ROX), are still legally and widely used in food animal production in many countries. This study was conducted to systematically characterize the content and speciation of arsenic in chicken tissues from live poultry markets and in commercial chicken feeds in Guangdong, a major poultry production and consumption province in China, and to assess the corresponding public health risk. The total arsenic contents in the commercial feeds could be modeled as a mixture of two log-normal distributions (geometric means: 0.66 and 17.5 mg/kg), and inorganic arsenic occurred at high levels (0.19-9.7 mg/kg) in those with ROX detected. In general, chicken livers had much higher contents of total arsenic compared to the muscle tissues (breast and drumstick), and chicken muscle from the urban markets contained arsenic at much higher levels than that from the rural markets. The incremental lifetime cancer risk (bladder and lung cancer) from dietary exposure to arsenic contained in chicken meat products on local markets was above the serious or priority level (10 -4 ) for 70% and 30% of the adult populations in Guangzhou and Lianzhou, respectively. These findings indicate the significant need to phase out the use of arsenic-based feed additives in China.

Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoTe 2 offers tremendous opportunities in various device applications. However, most of the existing methods so far only address the small-area local phase change or the growth of certain kinds of phases of MoTe 2 film by laser irradiation, mechanical strain, or procursor type. Obtaining facile, tunable, reversible, and continuous-phase transition and evolution between different phases in direct growth of large-area, few-layer MoTe 2 still remains challenging. Here, we develop a facile method to achieve phase control and transition and report a highly tunable, tellurization velocity-dependent metallic-semiconducting-metallic phase evolution in chemical vapor deposition (CVD) growth of large-area, few-layer MoTe 2 . We found four different phase stages, including two different types of coexistence phases of both 2H and 1 T' phases, 100% 2H phase, and 100% 1T' phase, would emerge, relying on the adopted tellurization velocity. Importantly, the tellurization velocity should be extremely controlled to obtain 100% 2H phase MoTe 2 , while 100% 1T' phase requires a fast tellurization velocity. We further found that such metallic-semiconducting-metallic phase evolution took place with a homogeneous spatial distribution and differs from previous reports in which obvious phase separations are usually found during the phase transition. The resulting MoTe 2 shows high quality with room-temperature mobility comparable with mechanically exfoliated materials. The results might impact large-scale phase engineering of TMDs and other 2D materials for Weyl semimetal topological physics and potential 2D semiconductor device applications.

Copper(II) bromide (CuBr2) salt has been applied to dope poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer (HTL) in polymer solar cells (PSCs), improving dramatically the conductivity of PEDOT:PSS film and consequently the device power conversion efficiency (PCE). Under the optimized doping concentration of CuBr2 of 10 mmol·L(-1), PCE of the CuBr2:PEDOT:PSS HTL-incorporated BHJ-PSC device based on poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5- (4',7'-di-2-thienyl-2',1',3'- benzothiadiazole) (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) (PCDTBT:PC71BM) reaches 7.05%, which is improved by ∼20.7% compared to that of the reference device based on pristine PEDOT:PSS HTL (5.84%) and represents the highest PCE for PCDTBT:PC71BM-based PSC devices without an electron transport layer (ETL) reported so far. The dramatic improvement of the conductivity of PEDOT:PSS film is interpreted by the weakening of the Coulombic attractions between PEDOT and PSS components. The work function of CuBr2:PEDOT:PSS slightly increases compared to that of the undoped PEDOT:PSS as inferred from scanning Kelvin probe microscopy (SKPM) measurements, contributing to the improved PCE due to the increases of the open-current voltage (Voc) and fill factor (FF).

Three amino-containing small-molecule organic materials-biuret, dicyandiamide (DCDA), and urea-were successfully applied as novel cathode buffer layers (CBLs) in P3HT:PCBM bulk heterojunction polymer solar cells (BHJ-PSCs) for the first time, resulting in obvious efficiency enhancement. Under the optimized condition, the power conversion efficiencies (PCEs) of the CBL-incorporated BHJ-PSC devices are 3.84%, 4.25%, and 4.39% for biuret, DCDA, and urea, which are enhanced by ∼15%, ∼27%, and ∼31%, respectively, compared to the reference poly(3-hexylthiophene-2,5-diyl) : [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) BHJ-PSC device without any CBL. The efficiency enhancement is primarily attributed to the increases of both short-circuit current density (Jsc) and fill factor (FF), for which the enhancement ratio is found to be sensitively dependent on the molecular structure of small-molecule organic materials. The surface morphologies and surface potential changes of the CBL-incorporated P3HT:PCBM photoactive layers were studied by atomic force microscopy and scanning Kelvin probe microscopy, respectively, suggesting the formation of an interfacial dipole layer between the photoactive layer and Al cathode, which may decrease the energy level offset between the work function of Al and the lowest unoccipoed molecular orbital level (LUMO) of the PCBM acceptor and consequently facilitate electron extraction by the Al cathode. The difference in the enhancement effect of biuret, DCDA, and urea is due to their difference on the work function matching with P3HT:PCBM. Besides, the coordination interaction between the lone-pair electrons on the N atoms of the amino (-NH2) group and the Al atoms may prohibit interaction between Al and the thiophene rings of P3HT, contributing to the efficiency enhancement of the CBL-incorporated devices as well. In this sense, the different CBL performance of biuret, DCDA, and urea is also proposed to partially originate from the differences on their chemical structure, specifically the number of amino groups.

A non-conjugated polymer poly(vinylpyrrolidone) (PVP) was applied as a new cathode buffer layer in P3HT:PCBM bulk heterojunction polymer solar cells (BHJ-PSCs), by means of either spin coating or self-assembly, resulting in significant efficiency enhancement. For the case of incorporation of PVP by spin coating, power conversion efficiency (PCE) of the ITO/PEDOT:PSS/P3HT:PCBM/PVP/Al BHJ-PSC device (3.90%) is enhanced by 29% under the optimum PVP spin-coating speed of 3000 rpm, which leads to the optimum thickness of PVP layer of ~3 nm. Such an efficiency enhancement is found to be primarily due to the increase of the short-circuit current (J(sc)) (31% enhancement), suggesting that the charge collection increases upon the incorporation of a PVP cathode buffer layer, which originates from the conjunct effects of the formation of a dipole layer between P3HT:PCBM active layer and Al electrodes, the chemical reactions of PVP molecules with Al atoms, and the increase of the roughness of the top Al film. Incorporation of PVP layer by doping PVP directly into the P3HT:PCBM active layer leads to an enhancement of PCE by 13% under the optimum PVP doping ratio of 3%, and this is interpreted by the migration of PVP molecules to the surface of the active layer via self-assembly, resulting in the formation of the PVP cathode buffer layer. While the formation of the PVP cathode buffer layer is fulfilled by both fabrication methods (spin coating and self-assembly), the dependence of the enhancement of the device performance on the thickness of the PVP cathode buffer layer formed by self-assembly or spin coating is different, because of the different aggregation microstructures of the PVP interlayer.