Chen Weijie

Sodium-ion batteries (SIBs) offer a promise of a scalable, low-cost, and environmentally benign means of renewable energy storage. However, the low capacity and poor rate capability of anode materials present an unavoidable challenge. In this work, it is demonstrated that surface phosphorylated TiO₂ nanotube arrays grown on Ti substrate can be efficient anode materials for SIBs. Fabrication of the phosphorylated nanoarray film is based on the electrochemical anodization of Ti metal in NH₄F solution and subsequent phosphorylation using sodium hypophosphite. The phosphorylated TiO₂ nanotube arrays afford a reversible capacity of 334 mA h g⁻¹ at 67 mA g⁻¹, a superior rate capability of 147 mA h g⁻¹ at 3350 mA g⁻¹, and a stable cycle performance up to 1000 cycles. In situ X-ray diffraction and transmission electron microscopy reveal the near-zero strain response and robust mechanical behavior of the TiO₂ host upon (de)sodiation, suggesting its excellent structural stability in the Na⁺ storage application.

TiO₂ nanotube arrays on a Ti substrate functionalized by surface phosphorylation are directly adapted as efficient anodes for sodium-ion batteries. Benefiting from synergy of unique nanotube structure, 3D array architecture, and high surface reactivity, the TiO₂ arrays afford a high reversible capacity of 334 mA h g⁻¹ and a superior rate capability of 147 mA h g⁻¹ at 3350 mA g⁻¹.

Cs-substituted mixed cation hybrid perovskites are promising materials for solar cell applications. In article number 1703835, Yabing Qi and co-workers report a scalable fabrication method (HCVD-CE) combining hybrid chemical vapor deposition and cation exchange to prepare Cs-substituted mixed cation perovskite solar cells. Devices prepared by this method show high power conversion efficiencies (PCE), low PCE loss/area, and excellent device stability.

The use of perovskite materials as anion-based intercalation pseudocapacitor electrodes has received significant attention in recent years. Notably, these materials, characterized by high oxygen vacancy concentrations, do not require high surface areas to achieve a high energy storage capacity as a result of the bulk intercalation mechanism. This study reports that reduced PrBaMn₂O_6–δ (r-PBM), possessing a layered double perovskite structure, exhibits ultrahigh capacitance and functions as an excellent oxygen anion-intercalation-type electrode material for supercapacitors. Formation of the layered double perovskite structure, as facilitated by hydrogen treatment, is shown to significantly enhance the capacitance, with the resulting r-PBM material demonstrating a very high gravimetric capacitance of 1034.8 F g⁻¹ and an excellent volumetric capacitance of ≈2535.3 F cm⁻³ at a current density of 1 A g⁻¹. The resultant formation of a double perovskite crystal oxide with a specific layered structure leads to the r-PBM with a substantially higher oxygen diffusion rate and oxygen vacancy concentration. These superior characteristics show immense promise for their application as oxygen anion-intercalation-type electrodes in pseudocapacitors.

The formation of a double perovskite crystal oxide with a specific layered structure results in the reduced PrBaMn₂O_6-δ (r-PBM) with a substantially higher oxygen diffusion rate and oxygen vacancy concentration. These factors are highly beneficial to the oxygen vacancies as charge storage sites can be applied in the pseudocapacitors with an oxygen ion intercalation process.

Facile control over the morphology of phase pure tin monosulfide (SnS) thin films, a promising future absorber for thin film solar cells, is enabled by controlling the growth kinetics in vapor transport deposition of congruently evaporated SnS. The pressure during growth is found to be a key factor in modifying the final shape of the SnS grains. The optimized cube-like SnS shows p-type with the apparent carrier concentration of ≈10¹⁷ cm⁻³ with an optical bandgap of 1.32 eV. The dense and flat surface morphology of 1 µm thick SnS combined with the minimization of pinholes directly leads to improved diode quality and increased shunt resistance of the SnS/CdS heterojunction (cell area of 0.30 cm²). An open-circuit voltage of up to 0.3068 V is achieved, which is independently characterized at the Korea Institute of Energy Research (KIER). Detailed high-resolution transmission electron microscopy analysis confirms the absence of detrimental secondary phases such as Sn₂S₃ or SnS₂ in the SnS grains or at intergrain boundaries. The initial efficiency level of 98.5% is maintained even after six months of storage in air, and the final efficiency of the champion SnS/CdS cell, certified at the KIER, is 2.938% with an open-circuit voltage of 0.2912 V.

Facile control on morphology of phase pure tin monosulfide (SnS) thin films is enabled by controlling the growth kinetics in vapor transport deposition. Dense and flat surface morphology of cube-like orthorhombic SnS combined with the minimized pinholes directly leads to improved diode quality and increased shunt resistance of the SnS/CdS heterojunction, achieving the certified efficiency of 2.938%.

Perovskite solar cells (PSCs) have gained a promising position during the past few years. However, as far as it goes, there is rare combination of the merits of metal–organic framework with PSCs. In this work, a 3D metal–organic framework, namely, [In₂(phen)₃Cl₆]·CH₃CN·2H₂O (In2) is first introduced into hole transport material of PSCs through band alignment engineering. By this facile strategy, the pinholes in the hole transport layer are effectively reduced, and the migration of Au into the entire PSC structure can be alleviated simultaneously. Meanwhile, In2 also plays a role in enhancing the light absorption of perovskite, which is due to: (1) the large particles of In2 acting as light scattering centers; (2) the emission wavelength of In2 is almost the same as the excitation wavelength of perovskite. Consequently, short-current density (J_sc), open circuit voltage (V_oc), and fill factor (FF) gain a significant increase from 19.53 to 21.03 mA cm⁻², 0.98 to 1.01 V, and 0.67 to 0.74, respectively. Thereby, the power conversion efficiency is remarkably enhanced from 12.8% to 15.8%. In the end, the stability of PSCs should also be improved.

The addition of [In₂(phen)₃Cl₆]·CH₃CN·2H₂O (In2) into the hole transport layer of perovskite solar cells (PSCs) through band alignment engineering is beneficial for charge transfer and restricts penetration of Au from back contact. Furthermore, the ultraviolet absorption, photoluminescence and light scattering properties of In2 can improve the light utilization of PSCs, leading to an increase in power conversion efficiency from 12.8% to 15.8%.

Straightforward evidence for ion-diffusion-induced interfacial degradation in inverted perovskite solar cells is presented. Over 1000 h, solar cells inevitably undergo degradation, especially with respect to the current density and fill factor. The Ag electrode is peeled off and re-evaporated to investigate the effect of the Ag/[6,6]-phenyl C71 butyric acid methyl ester (PCBM) interfacial degradation on the photovoltaic performance at days 10 (240 h), 20 (480 h), 30 (720 h), and 40 (960 h). The power conversion efficiency increases after the Ag electrode restoration process. While the current density shows a slightly decreased value, the fill factor and open-circuit voltage increase for the new electrode devices. The decrease in the activation energy due to the restored Ag electrode induces recovery of the fill factor. The diffused I⁻ ions react with the PCBM molecules, resulting in a quasi n-doping effect of PCBM. Upon electrode exchange, the reversible interaction between the iodine ions and PCBM causes current density variation. The disorder model for the open-circuit voltage over a wide range of temperatures explains the open-circuit voltage increase at every electrode exchange. Finally, the degradation mechanism of the inverted perovskite solar cell over 1000 h is described under the proposed recombination system.

An interfacial degradation mechanism of inverted perovskite solar cells is proposed. The Ag electrode is peeled off and re-evaporated to investigate the [6,6]-phenyl C71 butyric acid methyl ester/Ag interfacial degradation. Through an electrode restoration process, the degradation sources are eliminated, and the photovoltaic parameter variation is explained in detail.

In this work, a new benzo[1,2-b:4,5-b′]dithiophene (BDT) building block containing alkylthio naphthyl as a side chain is designed and synthesized, and the resulting polymer, namely PBDTNS-BDD, shows a lower HOMO energy level than that of its alkoxyl naphthyl counterpart PBDTNO-BDD. An optimized photovoltaic device using PBDTNS-BDD as a donor exhibits power conversion efficiencies (PCE) of 8.70% and 9.28% with the fullerene derivative PC₇₁BM and the fullerene-free small molecule ITIC as acceptors, respectively. Surprisingly, ternary blend devices based on PBDTNS-BDD and two acceptors, namely PC₇₁BM and ITIC, shows a PCE of 11.21%, which is much higher than that of PBDTNO-BDD based ternary devices (7.85%) even under optimized conditions.

Ternary blend devices containing a new building block show much better power conversion efficiencies than their corresponding binary counterparts. These new building blocks contain alkylthio naphthyl as a side chain. Blending with two acceptors, PC₇₁BM and ITIC, results in PBDTNS-BDD devices with a power conversion efficiency of 11.21%, which is much higher than that of the PBDTNO-BDD (7.85%) analogue under optimized conditions.

Multijunction solar cells are designed to improve the overlap with the solar spectrum and to minimize losses due to thermalization. Aside from the optimum choice of photoactive materials for the respective sub-cells, a proper interconnect is essential. This study demonstrates a novel all-oxide interconnect based on the interface of the high-work-function (WF) metal oxide MoO_x and low-WF tin oxide (SnO_x). In contrast to typical p-/n-type tunnel junctions, both the oxides are n-type semiconductors with a WF of 5.2 and 4.2 eV, respectively. It is demonstrated that the electronic line-up at the interface of MoO_x and SnO_x comprises a large intrinsic interface dipole (≈0.8 eV), which is key to afford ideal alignment of the conduction band of MoO_x and SnO_x, without the requirement of an additional metal or organic dipole layer. The presented MoO_x/SnO_x interconnect allows for the ideal (loss-free) addition of the open circuit voltages of the two sub-cells.

A novel all-oxide recombination interconnect for organic tandem solar cells is reported. A large interface dipole between the high-work-function (WF) metal oxide MoO_x and low-WF tin oxide (SnO_x) affords ideal alignment of the conduction band of the two n-type metal oxides. The actual recombination of electrons with holes occurs at the interface of organic/MoO_x of the lower sub-cell.

The fabrication of a new type of solar cell encapsulation architecture comprising a periodic array of step-index waveguides is reported. The materials are fabricated through patterning with light in a photoreactive binary blend of crosslinking acrylate and urethane, wherein phase separation induces the spontaneous, directed formation of broadband, cylindrical waveguides. This microstructured material efficiently collects and transmits optical energy over a wide range of entry angles. Silicon solar cells comprising this encapsulation architecture show greater total external quantum efficiencies and enhanced wide-angle light capture and conversion. This is a rapid, straightforward, and scalable approach to process light-collecting structures, whereby significant increases in cell performance may be achieved.

Broadband waveguide array architectures are inscribed into polymer films as a new encapsulant material for solar cells. The architectures are grown in a binary-component, photocurable resin through light-induced self-writing, which elicits spontaneous formation of the core–cladding waveguide profile. Their light-collecting and light-guiding functions are inherited by the film, thereby enabling large-scale enhanced and wide-angle optical energy collection and conversion.

Most nonfullerene acceptors developed so far for high-performance organic solar cells (OSCs) are designed in planar molecular geometry containing a fused-ring core. In this work, a new nonfullerene acceptor of DF-PCIC is synthesized with an unfused-ring core containing two cyclopentadithiophene (CPDT) moieties and one 2,5-difluorobenzene (DFB) group. A nearly planar geometry is realized through the F···H noncovalent interaction between CPDT and DFB for DF-PCIC. After proper optimizations, the OSCs with DF-PCIC as the acceptor and the polymer PBDB-T as the donor yield the best power conversion efficiency (PCE) of 10.14% with a high fill factor of 0.72. To the best of our knowledge, this efficiency is among the highest values for the OSCs with nonfullerene acceptors owning unfused-ring cores. Furthermore, no obvious morphological changes are observed for the thermally treated PBDB-T:DF-PCIC blended films, and the relevant devices can keep ≈70% of the original PCEs upon thermal treatment at 180 °C for 12 h. This tolerance of such a high temperature for so long time is rarely reported for fullerene-free OSCs, which might be due to the unique unfused-ring core of DF-PCIC. Therefore, the work provides new idea for the design of new nonfullerene acceptors applicable in commercial OSCs in the future.

A new nonfullerene acceptor (DF-PCIC) is designed and synthesized by utilizing noncovalent interactions. Organic solar cells (OSCs) with DF-PCIC as the acceptor exhibit the best efficiency of 10.14% with a high fill factor of 0.72. More importantly, excellent morphological stability is achieved for DF-PCIC-based devices, which is meaningful for the future practical applications of OSCs.