Quenching Detrimental Reactions and Boosting Hole Extraction via Multifunctional NiOx /Perovskite Interface Passivation for Efficient and Stable Inverted Solar Cells.

Nickel oxide (NiOx ) is one of the most promising hole transport materials for inverted perovskite solar cells (PSCs). However, its application is severely restrained due to unfavorable interfacial reactions and insufficient charge carrier extraction. Herein, a multifunctional modification at the NiOx /perovskite interface is developed via introducing fluorinated ammonium salt ligand to synthetically solve the obstacles. Specifically, the interface modification can chemically convert detrimental Ni≥3+ to lower oxidation state, resulting in the elimination of interfacial redox reactions. Meanwhile, interfacial dipole is incorporated simultaneously to tune the work function of NiOx and optimize energy level alignment, which effectively promotes the charge carrier extraction. Therefore, the modified NiOx -based inverted PSCs achieve a remarkable power conversion efficiency (PCE) of 22.93%. Moreover, the unencapsulated devices obtain a significantly enhanced long-term stability, maintaining over 85% and 80% of the initial PCEs after storage in ambient air with a high relative humidity of 50-60% for 1000 h and continuous operation at maximum power point under one-sun illumination for 700 h, respectively.

Heteropolymer improves p-i junction in perovskite solar cells.

The p-i heterojunction imbedded underneath the perovskite layer plays a vital role in determining the efficiency and stability of inverted perovskite solar cells (PSCs). We found that poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) suffers from the severely chain entanglement resulting in poor contact with perovskite. In this work, PTAA layer was treated by poly[(2,6-(4,8-bis(5-(2-ethylhexylthio)-4-fluorothiophen-2-yl)-benzo[1,2-b:4,5-b'] dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl) benzo[1',2'-c:4',5'-c'] dithiophene-4,8-dione)] (PBDB-T-SF) diluted solution in chlorobenzene. PBDB-T-SF, which contains dual carbonyl groups in its backbones and suitable electronic levels, can spontaneously fill the voids in chlorobenzene-washed PTAA (nano-PTAA). This not only promotes the work function of the substrate but also strengthens the coherence between perovskite and the substrate. Blade coated PSC (0.09 cm2) containing PBDB-T-SF (s-PSCs) realized a power conversion efficiency (PCE) of 21.83 %. After aging for more than 2000 h, s-PSCs maintains 88 % of the initial efficiency which is only 59 % for the control devices.

Tuning Perovskite Surface Polarity via Dipole Moment Engineering for Efficient Hole-Transport-Layer-Free Sn-Pb Mixed-Perovskite Solar Cells.

Post-treatment has been recognized as one of the effective methods for passivating the underlying defects in perovskite solar cells (PSCs), but little attention has been paid to how to pick suitable passivation agents with diverse isomers for efficient PSCs, particularly for the tin-lead (Sn-Pb) mixed PSCs. Here, we introduce the dependence of the power conversion efficiency (PCE) on a dipole moment for surface passivator screening, in which we chose three trifluoromethyl-phenylethylamine hydroiodide (CF3-PEAI) isomers as surface-treatment materials for hole-transport-layer-free (HTL-free) Sn-Pb mixed PSCs. The different positions of the -CF3 group for the CF3-PEAI isomer result in different dipole moments, which influences the interaction between CF3-PEAI and lead iodide. The para position CF3 with the highest dipole moment exhibits a higher PCE than the ortho-position with a lower dipole moment, which is attributed to the large dipole moment on the surface that could tune the surface polarity from p-type to n-type, facilitating electron charge transport in the HTL-free Sn-Pb mixed PSCs. An ultrathin 2D layer is formed on the perovskite surface to passivate the surface defects, which is responsible for the enhancement of the PCE and stability of the PSCs. As a result, the open-circuit voltage (VOC) of the device is improved from 0.775 to 0.824 V, yielding a champion PCE of 20.17%, which is one of the highest PCEs among the reported HTL-free Sn-Pb mixed PSCs. The device also shows improved stability with remaining 75% of its initial PCEs after storage in N2 for 700 h.

Dual Optimization of Bulk and Interface via the Synergistic Effect of Ligand Anchoring and Hole Transport Dopant Enables 23.28% Efficiency Inverted Perovskite Solar Cells.

The crystalline morphology of perovskite film plays a key role in determining the stability and performance of perovskite solar cells (PSCs). In addition, the work function and conductivity of hole transport layer (HTL) have a great influence on the effciency of PSCs. Here, we develop a synergistic doping strategy to fabricate high-performance inverted PSCs, doping a functional nanographene (C78-AHM) into the poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) HTL, thus forming an HTL with higher conductivity, lower roughness, and frontier energy levels matching the perovskite absorber work function. On this basis, thiosemicarbazide (TSC) was doped into the precursor solution of perovskite as the grain and interface modifier to further improve the crystalline morphology of perovskite film. Compared with the current single passivation method, this codoping strategy can simultaneously reduce the surface and bulk defects of perovskite film and reduce the interface energy barrier. Eventually, high-quality TSC-doped perovskite films based on C78-AHM-doped PTAA HTL are obtained with over 2 µm sized grains, pinhole-free, and improved crystallinity. As a result, this synergistic doping strategy increases the efficiency of the device from 20.27% to 23.28%. Furthermore, the environmental and thermal stabilities of the devices are significantly improved. Therefore, this work provides a simple way for the preparation of other efficient optoelectronic devices.

Integrated Ideal-Bandgap Perovskite/Bulk-Heterojunction Solar Cells with Efficiencies > 24.

Here, the authors report a highly efficient integrated ideal-bandgap perovskite/bulk-heterojunction solar cell (IPBSC) with an inverted architecture, featuring a near infrared (NIR) polymer DTBTI-based bulk-heterojunction (BHJ) layer atop guanidinium bromide (GABr)-modified FA0.7 MA0.3 Pb0.7 Sn0.3 I3 perovskite film as the photoactive layer. The IPBSC shows cascade-like energy level alignment between the charge-extractionlayer/perovskite/BHJ and efficient passivation effect of BHJ on perovskite. Thanks to the well-matched energy level alignment and high-quality ideal bandgap-based perovskite film, an efficient charge transfer occurs between the charge-extraction-layer/perovskite/BHJ. Moreover, the NIR polymer DTBTI on the perovskite film leads to an improved NIR light response for the IPBSC. In addition, the O, S and N atoms in the DTBTI polymer yield a strong interaction with perovskite, which is conducive to reducing the defects of the perovskite and suppressing charge recombination. As a result, the solar cell achieves a power conversion efficiency (PCE) of 24.27% (certificated value at 23.4% with 0.283-volt voltage loss), currently the recorded efficiency for both IPBSCs and Pb-Sn alloyed PSCs, and which is over the highest efficiency of perovskite-organic tandem solar cell. Moreover, the thermal, humidity and long-term operational stabilities of the IPBSCs are also significantly improved compared with the control PSCs.

Highly Orientational Order Perovskite Induced by In situ-generated 1D Perovskitoid for Efficient and Stable Printable Photovoltaics.

Employing low-dimensional perovskite has been proven to be a promising approach to enhance the efficiency and stability of perovskite solar cells. Here, thiopheniformamidine hydrochloride is introduced into CH3 NH3 PbI3 -based printable mesoscopic perovskite solar cells, to form 1D iodide lead thiophenamidine (TFPbI3 ) in situ. This judiciously designed low-dimensional perovskite can effectively passivate the defect of perovskite and induce the perovskite crystals to grow in a direction perpendicular to the substrate. Thus, the obtained 1D@3D perovskite could suppress the charge recombination and promote the charge transfer significantly. Benefiting from its dual effect and robustness, a significantly improved power conversion efficiency of 17.42% is yielded. The authors also develop high-performance printable mesoscopic perovskite solar cells with a champion efficiency approaching 13% for aperture area about 11.8 cm2 , as well as outstanding operational stability, retaining 90% of the original power conversion efficiency after 1000 hours of continuous illumination at the maximum power point in air.

Water-Soluble Conjugated Polyelectrolyte Hole Transporting Layer for Efficient Sky-Blue Perovskite Light-Emitting Diodes.

An optimized charge transporting layer (CTL) under perovskite film is crucial for efficient photoelectric devices. Here, a new water-soluble conjugated polyeletrolyte (CPE) with CH3 NH3 + (MA+ ) counterion termed as TB(MA) is used as the hole transporting layer (HTL) instead of the acidic poly(3,4-ethylenedioxythiophene):poly-styrene sulfonate (PEDOT:PSS) in sky-blue perovskite light-emitting diodes (PeLEDs). The inherent hydrophilicity of CPE enables a well-growth of quasi-2D perovskite layer with uniform and compact morphology, enhanced crystallinity with rare defect density and excellent energy transfer, resulting in a high photoluminescence quantum yield (PLQY) up to 62.0%. Especially, the MA+ counterion is able to passivate the interfacial defects in the perovskite, which optimize the interfacial compatibility between HTL and perovskite film. Finally, efficient sky-blue PeLEDs, emitting at 488 nm, are fabricated with high external quantum efficiency (EQE) up to 13.5% by using CPE as HTL. In addition, due to the low-temperature processability of water-soluble CPE, an efficient flexible sky-blue PeLEDs based on PEN/ITO substrate is also obtained with high EQE of 8.3%. Using CPE as HTL is an effective strategy toward fabricating efficient blue PeLEDs.

A dual function-enabled novel zwitterion to stabilize a Pb-I framework and passivate defects for highly efficient inverted planar perovskite solar cells.

A novel zwitterion named bethanechol chloride (BTCC) was introduced to simultaneously stabilize a Pb-I framework and passivate defects for efficient inverted perovskite solar cells. The BTCC-assisted device yielded an elevated power conversion efficiency of 20.45% with an open-circuit voltage of 1.14 V.

Highly Efficient and Stable GABr-Modified Ideal-Bandgap (1.35 eV) Sn/Pb Perovskite Solar Cells Achieve 20.63% Efficiency with a Record Small Voc Deficit of 0.33 V.

1.5-1.6 eV bandgap Pb-based perovskite solar cells (PSCs) with 30-31% theoretical efficiency limit by the Shockley-Queisser model achieve 21-24% power conversion efficiencies (PCEs). However, the best PCEs of reported ideal-bandgap (1.3-1.4 eV) Sn-Pb PSCs with a higher 33% theoretical efficiency limit are <18%, mainly because of their large open-circuit voltage (Voc ) deficits (>0.4 V). Herein, it is found that the addition of guanidinium bromide (GABr) can significantly improve the structural and photoelectric characteristics of ideal-bandgap (≈1.34 eV) Sn-Pb perovskite films. GABr introduced in the perovskite films can efficiently reduce the high defect density caused by Sn2+ oxidation in the perovskite, which is favorable for facilitating hole transport, decreasing charge-carrier recombination, and reducing the Voc deficit. Therefore, the best PCE of 20.63% with a certificated efficiency of 19.8% is achieved in 1.35 eV PSCs, along with a record small Voc deficit of 0.33 V, which is the highest PCE among all values reported to date for ideal-bandgap Sn-Pb PSCs. Moreover, the GABr-modified PSCs exhibit significantly improved environmental and thermal stability. This work represents a noteworthy step toward the fabrication of efficient and stable ideal-bandgap PSCs.

Side-Chain Polymers as Dopant-Free Hole-Transporting Materials for Perovskite Solar Cells-The Impact of Substituents' Positions in Carbazole on Device Performance.

Side-chain polymers have the potential to be excellent dopant-free hole-transporting materials (HTMs) for perovskite solar cells (PSCs) because of their unique characteristics, such as tunable energy levels, high charge mobility, good solubility, and excellent film-forming ability. However, there has been less research focusing on side-chain polymers for PSCs. Here, two side-chain polystyrenes with triphenylamine substituents on carbazole moieties were designed and characterized. The properties of the side-chain polymers were tuned finely, including the photophysical and electrochemical properties and charge mobilities, by changing the positions of triphenylamine substituents on carbazole. Owing to the higher mobility and charge extraction ability, the polymer P2 with the triphenylamine substituent on the 3,6-positions of the carbazole unit showed higher performance with power conversion efficiency (PCE) of 18.45%, which was much higher than the PCE (16.78%) of P1 with 2,7-positions substituted. These results clearly demonstrated that side-chain polymers can act as promising HTMs for PSC applications and the performance of side-chain polymers could be optimized by carefully tuning the structure of the monomer, which provides a new strategy to design new kinds of side-chain polymers and obtain high-performance dopant-free HTMs.

High-Performance Sodium-Ion Batteries Based on Nitrogen-Doped Mesoporous Carbon Spheres with Ultrathin Nanosheets.

Hard carbon exhibits high theoretical capacity for sodium-ion batteries. However, its practical application suffers from low electric conductivity, poor electrochemical stability, and sluggish kinetics. To tackle these challenges, novel nitrogen-doped carbon spheres with mesopores, ultrathin nanostructure, and optimal graphitization are prepared by a three-step procedure. We find that the as-prepared sample (NMCSs-800) with an optimal structure and nitrogen content delivers a high reversible sodium storage capacity of 334.7 mA h/g at 50 mA/g and an ultrahigh rate performance of 93.9 mA h/g at 5 A/g, which is better than most state-of-the-art carbon materials. The improved energy storage capacity is attributed to its unique architecture and optimal nitrogen doping, which provide abundant active sites, defects, and voids. Moreover, kinetic analysis and in situ Raman spectroscopy results reveal adsorption and adsorption-intercalation mechanisms for Na+ storage in hard carbon at the slope region above 0.3 V and the other slope region of 0.3-0.02 V, respectively. We believe that our findings provide a novel tactic to design elaborate nanomaterials for the high-performance sodium-ion battery.

Evaluation of A-Site Ba2+-Deficient Ba1-x Co0.4Fe0.4Zr0.1Y0.1O3-δ Oxides as Electrocatalysts for Efficient Hydrogen Evolution Reaction.

Exploring earth-abundant and cost-effective catalysts with high activity and stability for a hydrogen evolution reaction (HER) is of great importance to practical applications of alkaline water electrolysis. Here, we report on A-site Ba2+-deficiency doping as an effective strategy to enhance the electrochemical activity of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ for HER, which is related to the formation of oxygen vacancies around active Co/Fe ions. By comparison with the benchmarking Ba0.5Sr0.5Co0.8Fe0.2O3-δ , one of the most spotlighted perovskite oxides, the Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3-δ oxide has lower overpotential and smaller Tafel slope. Furthermore, the Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3-δ catalyst is ultrastable in an alkaline solution. The enhanced HER performance originated from the increased active atoms adjacent to oxygen vacancies on the surface of the Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3-δ catalyst induced by Ba2+-deficiency doping. The low-coordinated active atoms and adjacent oxygen ions may play the role of heterojunctions that synergistically facilitate the Volmer process and thus render stimulated HER catalytic activity. The preliminary results suggest that Ba2+-deficiency doping is a feasible method to tailor the physical and electrochemical properties of perovskite, and that Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3-δ is a potential catalyst for HER.

Intensive Exposure of Functional Rings of a Polymeric Hole-Transporting Material Enables Efficient Perovskite Solar Cells.

A variety of dopant-free hole-transporting materials (HTMs) is effectively applied in perovskite solar cells (PSCs); however, HTMs with the additional function of HTM/perovskite interfacial optimization that is crucial to their photovoltaic performance are really limited. In this work, the design of an HTM bearing an intensive exposure of its functional aromatic rings to perovskite layer via side-chain engineering is attempted. With an edge-on orientation and a short distance to perovskite, this HTM was expected to display an excellent ability to extract holes from and passivate defects in the perovskite layer. To demonstrate this strategy, an alternating copolymer was constructed with a 2,5-di-2-ethylhexyloxy-1,4-phenylene unit and a bithiophene unit, and the PSC based on this polymer showed an ultrahigh short-circuit current density of 25.50 mA cm-2 , which was the highest so far presented by dopant-free organic HTMs. A comparable power conversion efficiency of 19.68% (certified: 19.5%) to that of a control 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) device (19.81%) was thus obtained, which is the highest value ever reported for mesoporous PSCs based on dopant-free polymeric HTMs.

Toward Highly Sensitive Polymer Photodetectors by Molecular Engineering.

Modified 3,4-ethylenedioxythiophene is employed as the conjugated side chain in conjugated polymers, which can significantly depress the dark current of the polymer photodetectors with little associated decrease in photovoltaic properties, thus enhanceing the detectivities. This approach can be applied to a variety of conjugated polymers covering a photoresponse range from UV to NIR.

Synthesis and application of poly(fluorene-alt-naphthalene diimide) as an n-type polymer for all-polymer solar cells.

A new alternating copolymer of fluorene and naphthalene diimide, PF-NDI, was synthesized and characterized. The highest power conversion efficiency of all-polymer solar cells based on P3HT:PF-NDI reached 1.63% with a relatively high fill factor of 0.66 by using 1,8-diiodooctane as a solvent additive to optimize the mixing morphology.

Effects of block length in copolymers based on regioregular oligothiophenes linked with electron-accepting units.

Copolymers with an alternating structure of regioregular oligo(3-hexylthiophene) (O3HT) with different lengths and 2,5-dibutyl-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) were synthesized through Stille coupling reaction. The light absorption of the copolymers can be rationally tuned to have a broad spectrum across the visible region by adjusting the length of O3HT. Organic solar cells fabricated with the copolymers and PCBM showed a broad photoresponse and a comparable efficiency to that of poly(3-hexylthiophene) (P3HT):PCBM cells. The external quantum efficiency and fluorescence spectra suggested that the intrachain energy transfer from the O3HT block to the vicinity of the DPP unit could limit the photovoltaic performance of the copolymers.