Chen Weijie

Herein, the authors use PEACl treatment to significantly improve the moisture‐resistance of the CsPbI2Br film. It is found that hydrophobic PEA+ forms on the CsPbI2Br surface, meanwhile, chlorine doped into the CsPbI2Br lattice leading to smaller lattice structure and improved crystallization quality. As a result, the present device achieves a high power conversion efficiency of 14.05% and much improved moisture resistance.

CsPbI₂Br has been recognized as a promising material for photovoltaic applications due to its excellent optoelectronic properties and compositional stability. Unfortunately, its desired perovskite phase is not stable in humid environments as it is spontaneously transformed into a yellow non‐perovskite phase. Herein, we present our strategy to use phenylethylammonium chlorine (PEACl) treatment to significantly improve the moisture‐resistance of the CsPbI₂Br film without compromising its high solar cell efficiency. It is found that: 1) small‐sized hydrophobic aromatic group PEA⁺ forms in the edge‐on orientation on the CsPbI₂Br surface and 2) smaller halide Cl⁻ is doped into the CsPbI₂Br lattice during post‐annealing, leading to a smaller lattice structure with beneficial crystallization quality. Compared with the reference sample without the PEACl treatment, the present device achieves a comparable power‐conversion efficiency of 14.05% and much improved moisture resistance.

Nanotwinned grain structures in the TiO₂ nanotube walls can be induced for “single‐walled” nanotubes via high‐temperature treatment in pure oxygen atmosphere. Such twinned nanotubes show a strongly enhanced conductivity and photogenerated charge transport compared to classical nanotubes and can lead to efficiencies of up to 10.23% in dye‐sensitized solar cells.

Abstract

Titania is one of the key materials used in 1D, 2D, and 3D nanostructures as electron transport media in energy conversion devices. In the present study, it is shown that the electronic properties of TiO₂ nanotubes can be drastically improved by inducing a nanotwinned grain structure in the nanotube wall. This structure can be exclusively induced for “single‐walled” nanotubes with a high‐temperature treatment in pure oxygen atmospheres. Nanotubes with a twinned grain structure within the tube wall show a strongly enhanced conductivity and photogenerated charge transport compared to classic nanotubes. This remarkable improvement is exemplified in the electronic properties by using nanotwinned TiO₂ nanotubes in dye‐sensitized solar cells where a significant increase in efficiency of up to 10.2% is achieved.

High‐performance air‐stable perovskite solar cells are obtained after embedding carbon nanodots and urea into the perovskite. The best device performance features a power conversion efficiency of 20.2%, with negligible hysteresis. The devices displays excellent air‐stability for over 500 h without any encapsulation under 40% humidity (25 °C).

Abstract

Carbonized bamboo‐derived carbon nanodots (CNDs) as efficient additives for application in perovskite solar cells (PSCs) are reported. These carboxylic acid‐ and hydroxyl‐rich CNDs interact with the perovskite through hydrogen bonds and, thereby, promote the carriers' lifetimes and realize high‐performance p–i–n PSCs having the structure indium tin oxide/NiO _x /CH₃NH₃PbI₃ (MAPbI₃)/PC₆₁BM/BCP/Ag. As a result of interactions between the CNDs and the perovskite, the presence of the nonvolatile CND additive increases the power conversion efficiency (PCE) of the PSC from 14.48% ± 0.39% to 16.47% ± 0.26%. Furthermore, adding urea, a Lewis base, increases the PCE to 20.2%—the result of a significant increase in the crystal size and a lower content of grain boundary defects and, therefore, longer carrier lifetimes. Cells containing these two additives (without encapsulation) exhibit excellent shelf‐life and air‐stability, maintaining their high PCEs after storage in air—at a temperature of 25 °C and a humidity of 40%—for over 500 h. This performance is among of the best ever reported for p–i–n PSC devices incorporating carbon‐based additives.

A balanced crystallinity of donor and acceptor is finely controlled by combining blade‐coating and ternary strategies in a PBDB‐T:PTB7‐Th:FOIC‐based organic solar cell, resulting in well‐matched hole and electron mobilities with a power conversion efficiency of 12.02%.

Abstract

As a prototype tool for slot‐die coating, blade‐coating exhibits excellent compatibility with large‐area roll‐to‐roll coating. A ternary organic solar cell based on PBDB‐T:PTB7‐Th:FOIC blends is fabricated by blade‐coating and exhibits a power conversion efficiency of 12.02%, which is one of the highest values for the printed organic solar cells in ambient environment. It is demonstrated that blade‐coating can enhance crystallization of these three materials, but the degree of induction is different (FOIC > PBDB‐T > PTB7‐Th). Thus, the blade‐coated PBDB‐T:FOIC device presents much higher electron mobility than hole mobility due to the very high crystallinity of FOIC. Upon the addition of PTB7‐Th into the blade‐coated PBDB‐T:FOIC blends, the crystallinity of FOIC decreases together with the corresponding electron mobility, due to the better miscibility between PTB7‐Th and FOIC. The ternary strategy not only maintains the well‐matched crystallinity and mobilities, but also increases the photocurrent with complementary light absorption as well as the Förster resonant energy transfer. Furthermore, small domains with homogeneously distributed nanofibers are observed in favor of the exciton dissociation and charge transport. This combination of blade‐coating and ternary strategies exhibits excellent synergistic effect in optimizing morphology, showing great potential in the large‐area fabrication of highly efficient organic solar cells.

LED technology breaks performance barrier

LED technology breaks performance barrier, Published online: 10 October 2018; doi:10.1038/d41586-018-06923-y

Cd _x Zn_{1– x} Te nanocrystals (NCs) are prepared and successfully applied to aqueous‐processed NC solar cells. The depletion region is continuously tuned from 130, 137, 171 to a champion thickness of 200 nm. The highest thickness ratio (74%) of depletion region to the active layer, the record power conversion efficiency (5.96%), and short‐circuit current (21.2 mA cm⁻²) are achieved among aqueous‐processed NC solar cells.

Abstract

Water soluble nanocrystals (NCs) are promising materials in aqueous‐processed solar cells because of their high extinction coefficient, low‐cost, and favorable photoelectric characteristics. However, the power conversion efficiency (PCE) of the present aqueous‐processed NC solar cells is restricted by the short depletion region of the active layer and limited Fermi level offset between NCs and the electron transport layer. Herein, these issues are effectively addressed by preparing Cd _x Zn_{1– x} Te NCs capped with 2‐aminoethanethiol hydrochloride. The introduction of Zn²⁺ into CdTe NCs widens the Fermi level offset from 0.68 to 0.74 eV, lengthens the depletion region from 130 to 137 nm, and hence brings obvious improvement in the open circuit voltage (V _oc) and fill factor. Especially, the depletion region is successfully tuned from 137 to 171 nm, and even lengthened to a record thickness of 200 nm based on aqueous‐processed solar cells. As a result, a champion thickness ratio (74%) of depletion region to active layer (200/270 nm) is achieved. A champion PCE of 5.96% and short‐circuit current (J _sc) of 21.2 mA cm⁻² are achieved among aqueous‐processed NC solar cells. This work provides a simple way to prepare polynary NCs and highlights a prospective method to develop more efficient and cost‐effective solution‐processed environment friendly solar cells.

Publisher Correction: Large electrostrictive response in lead halide perovskites

Publisher Correction: Large electrostrictive response in lead halide perovskites, Published online: 12 October 2018; doi:10.1038/s41563-018-0216-0

Publication date: December 2018

Source: Nano Energy, Volume 54

Author(s): Xiangtong Meng, Chang Yu, Xuepeng Zhang, Longlong Huang, Matthew Rager, Jiafu Hong, Jieshan Qiu, Zhiqun Lin

Abstract

Graphical abstract

The purity of tin (Sn) sources is vital in terms of Sn‐based perovskite solar cells’ fabrication. In article no. 1800136, Zhiwei Liu, Zuqiang Bian, and co‐workers propose a simple purification method to reduce the detrimental Sn⁴⁺ existing in the precursor solutions by adding Sn powder. Aft er purification, the efficiency of FASnI₃‐based solar cells prepared from 99% SnI₂ is elevated from 0.09% to a maximum value of 6.75% due to the improved morphology and lessened recombination loss.

In article no. 1800132, Jin‐Peng Yang, Nobuo Ueno, Satoshi Kera, and co‐workers perform observations of the top valence band structure of CH₃NH₃PbI₃ single crystals using angle‐resolved ultraviolet photoelectron spectroscopy of the cleaved single‐crystal surfaces. The combination of freshly cleaved crystal surfaces and determination of the exact orientation of the crystal axes using diffraction techniques successfully measures well‐determined crystal directions.

In article no. 1800123, Weiyan Wang, Weijie Song, and co‐workers demonstrate foldable polymer solar cells using ultrathin paper substrates to relieve strain, combined with foldable ZnO/ultrathin Ag/ZnO electrodes. The solar cells maintain 92% of the initial efficiency after 35 folding cycles.

Large‐area, semitransparent, and flexible all‐polymer photodetectors are realized by incorporating a pair of donor and acceptor polymers and by using a lamination method. Both sides of these all‐polymer photodetectors respond visible light signals with nearly identical D* over 1.0 × 10¹¹ Jones.

Abstract

Photodetectors, converting optical signals from specific wavelengths to electrical signals, have many applications on photoimaging, optical communication, and environmental monitoring. Solution‐processed organic photodetectors (OPDs) based on organic materials emerge promise especially for wearable electronics and smart buildings. In this work, new all‐polymer photodetectors (all‐PPDs) are developed based on bulk‐heterojunction active layers which incorporate a donor polymer and an acceptor polymer. The inverted all‐PPDs exhibit outstanding external quantum efficiency over 70%, low dark current density (J _d) of 1.1 × 10⁻⁸ A cm⁻², and high detectivity (D*) over 3.0 × 10¹² Jones with planar response over the entire visible range. It is one of the best‐performing all‐PPDs reported so far and is also comparable with many organic and inorganic photodetectors. By using lamination technique, large‐area, semitransparent, flexible, and “fully” polymeric photodetectors are successfully fabricated for the first time, with D* over 10¹¹ Jones for double‐side light detection. The results highlight the great potential for producing high‐performance all‐PPDs by taking advantages of various device architecture and solution‐processing techniques.

Highly efficient perovskite quantum‐dot light‐emitting diodes (QLEDs) through organic–inorganic hybrid ligand (OIHL) passivation strategy are reported. The OIHL‐passivated films exhibit enhanced radiative recombination and effective electrical transportation features, which make QLEDs have a maximum peak external quantum efficiency (EQE) of 16.48%, which is the most efficient in the field of perovskite‐based LEDs up to now.

Abstract

Perovskite quantum dots (QDs) with high photoluminescence quantum yields (PLQYs) and narrow emission peak hold promise for next‐generation flexible and high‐definition displays. However, perovskite QD films often suffer from low PLQYs due to the dynamic characteristics between the QD's surface and organic ligands and inefficient electrical transportation resulting from long hydrocarbon organic ligands as highly insulating barrier, which impair the ensuing device performance. Here, a general organic–inorganic hybrid ligand (OIHL) strategy is reported on to passivate perovskite QDs for highly efficient electroluminescent devices. Films based on QDs through OIHLs exhibit enhanced radiative recombination and effective electrical transportation properties compared to the primal QDs. After the OIHL passivation, QD‐based light‐emitting diodes (QLEDs) exhibit a maximum peak external quantum efficiency (EQE) of 16.48%, which is the most efficient electroluminescent device in the field of perovskite‐based LEDs up to date. The proposed OIHL passivation strategy positions perovskite QDs as an extremely promising prospect in future applications of high‐definition displays, high‐quality lightings, as well as solar cells.

By applying anisole, a one‐step antisolvent assistant spin‐coating method with an ultrawide process window to fabricate perovskite thin films is developed. The application of these films in n–i–p structured perovskite solar cells leads to a maximum PCE of 19.76% for a small area (0.14 cm²), 17.39% for a large area (1.08 cm²), and a large‐sized perovskite thin film of 196 cm².

Abstract

Photovoltaic technologies based on perovskite absorber materials have led this optoelectronic field into a brand‐new horizon. However, the present antisolvents used in the one‐step spin‐coating method always encounter problems with the very narrow process window. Herein, anisole is introduced into the one‐step spin‐coating method, and the technology is developed to fabricate perovskite thin films with ultrawide processing window with a dimethylformamide (DMF):dimethyl sulfoxide (DMSO) ratio varying from 6:4 to 9:1 in the precursor solution, anisole dripping time ranging from 5 to 25 s, and an antisolvent volume varying from 0.1 to 0.9 mL. Perovskite thin films as large as 100 cm² are successfully fabricated using this method. Maximum photoelectric conversion efficiencies of 19.76% for small‐area (0.14 cm²) and 17.39% for large‐area (1.08 cm²) perovskite solar cell devices are obtained. It is also found that there are intermolecular hydrogen‐bonding forces between anisole and DMF/DMSO that play critical roles in the wide process window. These results provide a deeper understanding of the crystallizing procedure of perovskite during the one‐step spin‐coating process.

Recent advances in Ruddlesden–Popper quasi‐2D perovskites are reported. After detailed comparison of the crystal structure, growth mechanism, charge‐transport properties, and carrier dynamics in 2D and 3D perovskites, the advantages and challenges of quasi‐2D perovskites are discussed. Finally, electron–phonon interactions and polaritonic emissions in these materials are reviewed.

Abstract

Following the rejuvenation of 3D organic–inorganic hybrid perovskites, like CH₃NH₃PbI₃, (quasi)‐2D Ruddlesden–Popper soft halide perovskites R₂A _{n −1}Pb _n X_{3 n +1} have recently become another focus in the optoelectronic and photovoltaic device community. Although quasi‐2D perovskites were first introduced to stabilize optoelectronic/photovoltaic devices against moisture, more interesting properties and device applications, such as solar cells, light‐emitting diodes, white‐light emitters, lasers, and polaritonic emission, have followed. While delicate engineering design has pushed the performance of various devices forward remarkably, understanding of the fundamental properties, especially the charge‐transfer process, electron–phonon interactions, and the growth mechanism in (quasi)‐2D halide perovskites, remains limited and even controversial. Here, after reviewing the current understanding and the nexus between optoelectronic/photovoltaic properties of 2D and 3D halide perovskites, the growth mechanisms, charge‐transfer processes, vibrational properties, and electron–phonon interactions of soft halide perovskites, mainly in quasi‐2D systems, are discussed. It is suggested that single‐crystal‐based studies are needed to deepen the understanding of the aforementioned fundamental properties, and will eventually contribute to device performance.

The 2D Ti₃C₂T _x additive can enlarge the grain size of the perovskite film due to the weak interactions between the termination groups (F and OH) and CH₃NH₃I. Due to these interactions, the perovskite nuclei generate around the additive and the number of nuclei is suppressed. Fewer nuclei make the grain size larger than that of the pristine film.

Abstract

MXenes, a newly intriguing family of 2D materials, have recently attracted considerable attention owing to their excellent properties such as high electrical conductivity and mobility, tunable structure, and termination groups. Here, the Ti₃C₂T _x MXene is incorporated into the perovskite absorber layer for the first time, which aims for efficiency enhancement. Results show that the termination groups of Ti₃C₂T _x can retard the crystallization rate, thereby increasing the crystal size of CH₃NH₃PbI₃. It is found that the high electrical conductivity and mobility of MXene can accelerate the charge transfer. After optimizing the key parameters, 12% enhancement in device performance is achieved by 0.03 wt% amount of MXene additive. This work unlocks opportunities for the use of MXene as potential materials in perovskite solar cell applications.

Optimized ternary organic solar cells (OSCs) exhibit a power conversion efficiency of 12.55% with simultaneously improved J _SC and fill factor due to the complementary absorption spectra and good compatibility of MeIC and MeIC2. The two acceptors with good compatibility and similar lowest unoccupied molecular orbital levels may prefer to form one alloyed state for efficient electron transport in ternary OSCs.

Abstract

Efficient ternary organic solar cells (OSCs) are fabricated by employing a polymer PBT1‐C as the donor and two non‐fullerene materials, MeIC and MeIC2, as one alloyed acceptor. The optimized ternary OSCs with 30 wt% MeIC2 in acceptors achieve a power conversion efficiency (PCE) of 12.55%, which is much higher than that of 11.47% for MeIC‐based binary OSCs and 11.41% for MeIC2‐based binary OSCs. The >9.4% improvement in PCE is mainly attributed to the optimized photon harvesting and morphology of ternary active layers, resulting in the simultaneously improved short‐circuit current and fill factor. Furthermore, good compatibility and similar lowest unoccupied molecular orbital energy levels of MeIC and MeIC2 are beneficial to form one alloyed acceptor for efficient electron transport in the ternary active layers. This work may provide new insight when selecting the third component for preparing efficient ternary OSCs.

Stable α‐CsPbI₃ is synthesized by incorporating cation 2‐(naphthalene‐1‐yl)ethanamine (NEA) for perovskite‐based light‐emitting diodes (PeLED). A high external quantum (EQE) of 8.65% is successfully demonstrated for the characteristic red emission ≈682 nm representing the highest value among Cs‐based red PeLEDs up to now. More importantly, corresponding PeLEDs exhibit outstanding stability with EQE retaining 90% after 3 months storage.

Abstract

Recently, inorganic cesium–lead halide perovskites with high thermal stability have attracted much attention as promising light‐emitting material for research of perovskite‐based light‐emitting diodes (PeLEDs) toward high‐definition displays. However, the CsPbI₃‐based red PeLEDs still suffer low external quantum efficiency (EQE) and poor device stability due to the spontaneous phase transition from cubic CsPbI₃ (α‐CsPbI₃) to nonradiative orthorhombic phase (δ‐CsPbI₃) under ambient conditions. Here, a feasible approach is reported on phase engineering by incorporating the long‐chain cation (e.g., 2‐(naphthalene‐1‐yl)ethanamine (NEA)) in CsPbI₃ for stable and high‐performance CsPbI₃‐based red light‐emitting diodes (LEDs). A high EQE of 8.65% is successfully achieved for the characteristic red emission at ≈682 nm representing the highest value among Cs‐based red PeLEDs up to now. More importantly, the corresponding PeLEDs exhibit outstanding stability with EQE retaining 90% after 3 months of storage. These results verify the potential of using cesium‐based inorganic perovskite as viable alternatives to methylammonium (MA)‐ or formamidinium (FA)‐based perovskite for desirable practical applications.