Organic–inorganic perovskites with intriguing optical and electrical properties have attracted significant research interests due to their excellent performance in optoelectronic devices. Recent ...efforts on preparing uniform and large‐grain polycrystalline perovskite films have led to enhanced carrier lifetime up to several microseconds. However, the mobility and trap densities of polycrystalline perovskite films are still significantly behind their single‐crystal counterparts. Here, a facile topotactic‐oriented attachment (TOA) process to grow highly oriented perovskite films, featuring strong uniaxial‐crystallographic texture, micrometer‐grain morphology, high crystallinity, low trap density (≈4 × 1014 cm−3), and unprecedented 9 GHz charge‐carrier mobility (71 cm2 V−1 s−1), is demonstrated. TOA‐perovskite‐based n‐i‐p planar solar cells show minimal discrepancies between stabilized efficiency (19.0%) and reverse‐scan efficiency (19.7%). The TOA process is also applicable for growing other state‐of‐the‐art perovskite alloys, including triple‐cation and mixed‐halide perovskites.
A facile topotactic‐oriented attachment process can produce uniaxially oriented perovskite thin films with micrometer‐grain morphology, high crystallinity, low trap density (≈4 × 1014 cm−3), and fast 9 GHz charge‐carrier mobility (71 cm2 V−1 s−1). The n‐i‐p planar perovskite solar cell exhibits a power conversion efficiency of 19.7% (with stabilized efficiency output of 19.0%).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
To boost the photoelectrochemical water oxidation performance of hematite photoanodes, high temperature annealing has been widely applied to enhance crystallinity, to improve the interface ...between the hematite-substrate interface, and to introduce tin-dopants from the substrate. However, when using additional dopants, the interaction between the unintentional tin and intentional dopant is poorly understood. Here, using germanium, we investigate how tin diffusion affects overall photoelectrochemical performance in germanium:tin co-doped systems. After revealing that germanium is a better dopant than tin, we develop a facile germanium-doping method which suppresses tin diffusion from the fluorine doped tin oxide substrate, significantly improving hematite performance. The NiFeO
x
@Ge-PH photoanode shows a photocurrent density of 4.6 mA cm
−2
at 1.23 V
RHE
with a low turn-on voltage. After combining with a perovskite solar cell, our tandem system achieves 4.8% solar-to-hydrogen conversion efficiency (3.9 mA cm
−2
in NiFeO
x
@Ge-PH/perovskite solar water splitting system). Our work provides important insights on a promising diagnostic tool for future co-doping system design.
Goldschmidt tolerance factor (t) is an empirical index for predicting stable crystal structures of perovskite materials. A t value between 0.8 and 1.0 is favorable for cubic perovskite structure, and ...larger (>1) or smaller (<0.8) values of tolerance factor usually result in nonperovskite structures. CH(NH2)2PbI3 (FAPbI3) can exist in the perovskite α-phase (black phase) with good photovoltaic properties. However, it has a large tolerance factor and is more stable in the hexagonal δH-phase (yellow phase), with δH-to-α phase-transition temperature higher than room temperature. On the other hand, CsPbI3 is stabilized to an orthorhombic structure (δO-phase) at room temperature due to its small tolerance factor. We find that, by alloying FAPbI3 with CsPbI3, the effective tolerance factor can be tuned, and the stability of the photoactive α-phase of the mixed solid-state perovskite alloys FA1–x Cs x PbI3 is enhanced, which is in agreement with our first-principles calculations. Thin films of the FA0.85Cs0.15PbI3 perovskite alloy demonstrate much improved stability in a high-humidity environment; this contrasts significantly with the pure FAPbI3 film for which the α-to-δH phase transition (associated with yellowing appearance) is accelerated by humidity environment. Due to phase stabilization, the FA0.85Cs0.15PbI3 solid-state alloy showed better solar cell performance and device stability than its FAPbI3 counterparts. Our studies suggest that tuning the tolerance factor through solid-state alloying can be a general strategy to stabilize the desired perovskite structure for solar cell applications.
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The development of kesterite Cu2ZnSn(S,Se)4 thin‐film solar cells is currently hindered by the large deficit of open‐circuit voltage (Voc), which results from the easy formation of CuZn antisite ...acceptor defects. Suppressing the formation of CuZn defects, especially near the absorber/buffer interface, is thus critical for the further improvement of kesterite solar cells. In this paper, it is shown that there is a large disparity between the defects in Cu‐ and Ag‐based kesterite semiconductors, i.e., the CuZn or CuCd acceptor defects have high concentration and are the dominant defects in Cu2ZnSn(S,Se)4 or Cu2CdSnS4, but the AgZn acceptor has only a low concentration and the dominant defects are donors in Ag2ZnSnS4. Therefore, the Cu‐based kesterites always show p‐type conductivity, while the Ag‐based kesterites show either intrinsic or weak n‐type conductivity. Based on this defect disparity and calculated band alignment, it is proposed that the Voc limit of the kesterite solar cells can be overcome by alloying Cu2ZnSn(S,Se)4 with Ag2ZnSn(S,Se)4, and the composition‐graded (Cu,Ag)2ZnSn(S,Se)4 alloys should be ideal light‐absorber materials for achieving higher efficiency kesterite solar cells.
A new strategy is proposed to overcome the Voc bottleneck and increase the efficiency of the kesterite solar cells. This is achieved by forming composition‐graded (Cu1–xAgx)2ZnSn(S,Se)4 alloys as the absorber layer.
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An all‐solid‐state lithium battery based on a sulfide electrolyte is one of the most promising next‐generation energy storage systems. However, the high interfacial impedance, particularly due to the ...internal pores in the electrode or electrolyte layers, is the major limiting factor to the development of sheet‐type all‐solid‐state batteries. In this study, a low‐resistance integrated all‐solid composite electrode is developed using a hybrid of a pyrrolidinium‐based ionic liquid and a polyethylene oxide polymer with lithium salt as a multifunctional interphase material, which is engineered to be compatible with the sulfide electrolyte as well as the fabrication process of sheet‐type composite electrode. The interphase material fills the pore in the composite sheet while binding the components together, which effectively increases the interfacial contact area and strengthens the physical network between the components, thereby enabling enhanced ion transport throughout the electrode. The interphase‐engineered sheet‐type LiNi0.8Co0.1Mn0.1O2 /Li10GeP2S12 electrode shows a high reversible capacity of 166 mAh g−1 at 25 °C, corresponding to 92% of the observed capacity in a current liquid‐based cathode system, as well as enhanced cycle and rate performances. This study proposes a novel and practical method for the development of high‐performance sheet‐type all‐solid‐state lithium batteries.
An interphase‐engineered sheet‐type LiNi0.8Co0.1Mn0.1O2/Li10GeP2S12 electrode is developed by applying a hybrid of PEO‐Pyr14TFSI‐LiTFSI as a multifunctional interphase material to be compatible with the sulfide electrolyte. It shows a high reversible capacity (92% utilization) with excellent cycling performance at 25 °C. This study provides a practical method for the development of intrinsically safe and high‐performance all‐solid‐state lithium batteries.
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Although the exceptional theoretical specific capacity (1672 mAh g−1) of elemental sulfur makes lithium–sulfur (Li–S) batteries attractive for upcoming rechargeable battery applications (e.g., ...electrical vehicles, drones, unmanned aerial vehicles, etc.), insufficient cycle lives of Li–S cells leave a substantial gap before their wide penetration into commercial markets. Among the key features that affect the cyclability, the shuttling process involving polysulfides (PS) dissolution is most fatal. In an effort to suppress this chronic PS shuttling, herein, a separator coated with poled BaTiO3 or BTO particles is introduced. Permanent dipoles that are formed in the BTO particles upon the application of an electric field can effectively reject PS from passing through the separator via electrostatic repulsion, resulting in significantly improved cyclability, even when a simple mixture of elemental sulfur and conductive carbon is used as a sulfur cathode. The coating of BTO particles also considerably suppresses thermal shrinkage of the poly(ethylene) separator at high temperatures and thus enhances the safety of the cell adopting the given separator. The incorporation of poled particles can be universally applied to a wide range of rechargeable batteries (i.e., metal‐air batteries) that suffer from cross‐contamination of charged species between both electrodes.
Poling for polysulfide rejection: The fatal shuttling process in lithium–sulfur batteries is effectively suppressed by “poled” BaTiO3 or BTO particles coated on a poly(ethylene) separator. The permanent dipoles of poled BTO particles repel polysulfides via electrostatic repulsion. The coating of BTO particles also provides a resistance against thermal shrinkage of the polyethylene separator at high temperature, thus enhancing the safety of the given cell.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Hematite (α-Fe
2
O
3
) is the most studied artificial oxygen-evolving photo-anode and yet its efficiency limitations and their origin remain unknown. A sub-picosecond reorganisation of the ...hematite structure has been proposed as the mechanism which dictates carrier lifetimes, energetics and the ultimate conversion yields. However, the importance of this reorganisation for actual device performance is unclear. Here we report an in situ observation of charge carrier self-localisation in a hematite device, and demonstrate that this process affects recombination losses in photoelectrochemical cells. We apply an ultrafast, device-based optical-control method to resolve the subpicosecond formation of small polarons and estimate their reorganisation energy to be ~0.5 eV. Coherent oscillations in the photocurrent signals indicate that polaron formation may be coupled to specific phonon modes (<100 cm
−1
). Our results bring together spectroscopic and device characterisation approaches to reveal new photophysics of broadly-studied hematite devices.
We investigate determinants of global knowledge sourcing of overseas R&D subsidiaries, shedding light on vertical cross-border embeddedness within firms. Drawing on the paradox of embeddedness ...perspective, which assumes that embeddedness may facilitate or hinder knowledge transfer, we examine the extent to which different types of internal vertical embeddedness – administrative versus knowledge – facilitate global knowledge sourcing. We find that vertical administrative embeddedness inhibits global knowledge sourcing, while vertical knowledge embeddedness promotes it. We also find differing moderating effects of geographic distance between headquarters and its subsidiaries on the association between vertical embeddedness and global knowledge sourcing.
Oxygen vacancies (OVs) are a mixed blessing for the photoelectrochemical (PEC) water oxidation performance of monoclinic tungsten trioxide (m‐WO3) photoanodes. Although it is widely accepted that a ...moderate concentration of OVs is beneficial for the PEC performance of the m‐WO3 photoanodes, this argument assumes a uniform distribution of OVs throughout the m‐WO3 crystal. In this case, only the overall concentration of OVs needs to be considered. However, the spatial non‐uniformity of OV defects in m‐WO3 photoanodes has not been thoroughly examined. In this study, by employing a m‐WO3 nanorod array as a model photoanode, the aim is to show that a higher OV concentration near the surface of m‐WO3 compared to that in the bulk is advantageous for the PEC performances of this material. In addition, a laser‐assisted defect control (LADC) process is employed to manipulate the spatial distribution of OVs in the m‐WO3 photoanodes to achieve enhanced PEC performances. Moreover, a one‐step laser deposition process is introduced to obtain an ultrathin FeNi oxygen evolution catalyst overlayer on the defect‐controlled m‐WO3 photoanodes, further improving PEC performance, photostability, and Faradaic efficiency.
This manuscript introduces a simple and novel scheme for oxygen vacancy engineering of monoclinic tungsten trioxide (m‐WO3). The proposed laser‐assisted defect control process enables the spatial distribution of oxygen vacancies in m‐WO3 photoanodes, resulting in the outstanding photoelectrochemical performance.
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Accurate calculation of the electronic band structure is essential to material screening and design. Hybrid density functional has been recently widely used to describe the electronic structure of ...semiconductors; however, it is difficult to locate the band edge positions of indirect band gap materials due to heavy computational cost especially when the band edges are not located at special k-points. We suggest how to investigate three-dimensional band structure efficiently with hybrid density functionals and to find the band edge positions. The band edge position of diamond Si, SbSI, and MoS2 are investigated using the proposed method.
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