Ligang Yuan

Electron backscatter diffraction (EBSD) combined with carrier lifetime, mobility, and diffusion length measurements, shows that optical and scanning electron microscopy images cannot accurately predict grain boundary positions or their resulting properties. Grain boundaries passivated by amorphous perovskite display increased photoluminescence lifetime and intensity. This suggests that crystallographic (not only chemical) effects play an important role in halide perovskite grain boundary properties.

Abstract

Grain boundaries play a key role in the performance of thin‐film optoelectronic devices and yet their effect in halide perovskite materials is still not understood. The biggest factor limiting progress is the inability to identify grain boundaries. Noncrystallographic techniques can misidentify grain boundaries, leading to conflicting literature reports about their influence; however, the gold standard – electron backscatter diffraction (EBSD) – destroys halide perovskite thin films. Here, this problem is solved by using a solid‐state EBSD detector with 6000 times higher sensitivity than the traditional phosphor screen and camera. Correlating true grain size with photoluminescence lifetime, carrier diffusion length, and mobility shows that grain boundaries are not benign but have a recombination velocity of 1670 cm s⁻¹, comparable to that of crystalline silicon. Amorphous grain boundaries are also observed that give rise to locally brighter photoluminescence intensity and longer lifetimes. This anomalous grain boundary character offers a possible explanation for the mysteriously long lifetime and record efficiency achieved in small grain halide perovskite thin films. It also suggests a new approach for passivating grain boundaries, independent of surface passivation, to lead to even better performance in optoelectronic devices.

The sulfonic zwitterion combines the functions of morphology tailoring and defect passivation together into one kind of functional molecule, and this “all‐in‐one” system provides a facile but effective pathway for the fabrication of high‐performance perovskite solar cells.

Abstract

Uniform and high‐electronic‐quality perovskite thin films are essential for high‐performance perovskite devices. Here, it is shown that the 3‐(decyldimethylammonio)‐propane‐sulfonate inner salt (DPSI), which is a sulfonic zwitterion, plays dual roles in tuning the crystallization behavior and passivating the defects of perovskites. The synergistic effect of crystallization control and defect passivation remarkably suppresses pinhole formation, reduces the charge trap density, and lengthens the carrier recombination lifetime, and thereafter boosts the small‐area (0.08 cm²) planar perovskite device efficiency to 21.1% and enables a high efficiency of 18.3% for blade‐coating large‐area (1 cm²) devices. The device also shows good light stability, which remains at 88% of the initial efficiency under continuous unfiltered AM 1.5G light illumination for 480 h. These findings provide an avenue for simultaneous crystallization control and defect passivation to further improve the performance of perovskite devices.

An ultra‐thin self‐assembly monolayer of methoxysilane on zinc oxide (ZnO) blocks the contact between perovskite and electron transport layer. It suppresses the decomposition of the perovskite film when annealed at 100 °C on a hotplate. After introducing a self‐form solvent annealing method to increase the crystallization, a ZnO based perovskite solar cell with a power conversion efficiency of 18.34% is obtained finally.

Although ZnO is an attractive electron transport layer (ETL) for high performance perovskite solar cells (PSCs) due to its suitable energy structure, high electron mobility, and low‐temperature process, perovskite films on ZnO are decomposed rapidly as the substrate is heated over 90 °C. However, the annealing temperature higher than 90 °C is mandatory to produce high quality perovskite films. Here, for the first time, the use of an ultra‐thin self‐assembly monolayer (SAM) of methoxysilane on ZnO ETL to suppress the decomposition of perovskite films is reported. A self‐form solvent annealing (SFSA) method is also carried out to improve the crystal quality of perovskite, and the champion device of SAM modified ZnO based PSCs yields a PCE of 18.34%. All these processes are conducted at low temperature and compatible with fabrication of flexible devices.

Conjugated polymers act as a hydrophobic interlayer with superb hole mobility between perovskite and doped spiro‐OMeTAD, enhancing the device stability and performance.

Hybrid organic–inorganic perovskite (HOIP) solar cells have achieved a certified power conversion efficiency (PCE) of 22.7%, which commonly use doped spiro‐OMeTAD as hole transport materials (HTMs). However, the additives in spiro‐OMeTAD can absorb moisture and cause the degradation of HOIP layers, leading to severe air‐instability of devices. Herein, conjugated polymers of PD‐10‐DTTE‐7 as a new effective interlayer between perovskite and doped spiro‐OMeTAD to achieve air‐stable efficient perovskite solar cells are reported. Its hydrophobic nature can effectively prevent the penetration of moisture and additives. Its superb hole mobility (9.54 cm² V⁻¹ s⁻¹, ≈10⁵ times higher than spiro‐OMeTAD) and suitable highest occupied molecular orbital level (−5.33 eV) are preferable to the hole injection and transport at the interface thus enhancing the device PCE. As a result, the MAPbI₃ solar cells with the PD‐10‐DTTE‐7 interlayer achieve remarkable device air‐stability and enhanced PCE, compared with the devices without the interlayer. These results provide a feasible approach to enhance solar cell stability and performance simultaneously.

The influence of the surface effect of 2D layered perovskites before and after mechanical exfoliation is studied. The smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current. This work reveals the strong dependence of the surface condition of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties.

Abstract

Despite the remarkable progress of optoelectronic devices based on hybrid perovskites, there are significant drawbacks, which have largely hindered their development as an alternative of silicon. For instance, hybrid perovskites are well‐known to suffer from moisture instability which leads to surface degradation. Nonetheless, the dependence of the surface effect on the moisture stability and optoelectronic properties of hybrid perovskites has not been fully investigated. In this work, the influence of the surface effect of 2D layered perovskites before and after mechanical exfoliation, representing rough and smooth surfaces of perovskite crystals, are studied. It is found that the smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current, which outperforms the rough perovskites by 23.6 times in terms of photodetectivity. The superior moisture stability of the smooth perovskites over the rough perovskites is demonstrated. Additionally, ethanolamine is employed as an organic linker of the 2D layered perovskite, which further improves the moisture stability. This work reveals the strong dependence of the surface conditions of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties, which are of utmost importance to the design of practical optoelectronic devices based on hybrid perovskite crystals.

Perovskite solar cells produced by roll‐to‐roll (R2R) slot die coating on flexible substrates at ambient atmosphere from nontoxic solvents demonstrate an average stabilized efficiency of 12%, with the best value of 13.5%. This study is the first public demonstration of R2R slot die coating of perovskites on 30 cm wide substrates with the deposition and drying speed of 3–5 m min⁻¹.

Abstract

The feasibility of upscaling the perovskite solar cells technologies to high volume production using roll‐to‐roll (R2R) slot die coating is demonstrated in this study. Perovskite solar cells are produced by R2R slot die coating on flexible substrates with a width of 30 cm and the web speed of 3–5 m min⁻¹. R2R deposition of the electron transport layer and perovskite is performed at ambient atmosphere from nontoxic solvents compatible with industrial manufacturing. The average stabilized power conversion efficiency of the devices made on different areas of the foil is 12%, with the best value of 13.5%. The demonstrated achievement is an important milestone and a big solid step toward future commercialization of perovskite‐based solar cells technologies.

In order to reduce the cost of hole transporting materials (HTMs) for perovskite solar cells, the amide‐bond is introduced in the backbone resulting in a straightforward synthesis. Despite the lack of conjugation, the here presented HTM (EDOT‐Amide‐TPA) outperforms state‐of‐the‐art materials in performance, showing over 20% power conversion efficiency, and stability, which is assigned to the unique properties of the amide‐bond.

Abstract

State‐of‐the‐art perovskite‐based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro‐OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT‐Amide‐TPA) is reported in which a functional amide‐based backbone is introduced, which allows this material to be synthesized in a simple condensation reaction with an estimated cost of <$5 g⁻¹. When employed in perovskite solar cells, EDOT‐Amide‐TPA demonstrates stabilized power conversion efficiencies up to 20.0% and reproducibly outperforms Spiro‐OMeTAD in direct comparisons. Time resolved microwave conductivity measurements indicate that the observed improvement originates from a faster hole injection rate from the perovskite to EDOT‐Amide‐TPA. Additionally, the devices exhibit an improved lifetime, which is assigned to the coordination of the amide bond to the Li‐additive, offering a novel strategy to hamper the migration of additives. It is shown that, despite the lack of a conjugated backbone, the amide‐based HTM can outperform state‐of‐the‐art HTMs at a fraction of the cost, thereby providing a novel set of design strategies to develop new, low‐cost HTMs.

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.

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.

Zn_0.8Cd_0.2S nanoparticles (ZCS) are doped in [6,6]‐phenyl‐C61‐butyric acid methyl (PCBM) to form an inorganic/organic hybrid as an efficient electron transport layer (ETL) in p‐i‐n planar perovskite solar cells. The ZCS@PCBM interlayer improves electron extraction, enhances electron transportation, and suppresses charge recombination. The shielding effect of ZCS nanoparticles can keep the perovskite from erosion by ambient moisture, thus improving the device stability.

In this study, an inorganic/organic hybrid, Zn_0.8Cd_0.2S nanoparticles (ZCS) embedded in [6,6]‐phenyl‐C61‐butyric acid methyl (PCBM), as an efficient electron transport layer (ETL) for air‐processed p‐i‐n perovskite solar cells (PSCs) has been demonstrated, and the doping effect and doping mechanism are systematically studied. As compared to PCBM, ZCS@PCBM ETL exhibits improved electron extraction at the perovskite/ETL interface, increased electron transportation within the ETL, enhanced charge collection efficiency, and suppressed interfacial charge recombination, resulting in significantly improved power conversion efficiency (PCE) from 14.41 to 17.18% by 19.2%. Interestingly, the ZCS nanoparticles can protect the perovskite layer from erosion by ambient moisture, and 82% of the initial PCE for the non‐encapsulated devices with ZCS@PCBM ETL is retained after 500 h storage in the atmosphere (humidity 30–60%) versus only 13% of the initial PCE for the PCBM ETL without ZCS doping.

The perovskite solar cell (PSC) has boosted its power conversion efficiency along with the application of inorganic hole transport layer (HTL). The presence of inorganic HTL assist the carrier transport and improve the stability. Wide variety of inorganic HTLs are reviewed in this report along with their properties, synthesis technique and interfacial chemistry and carrier dynamic.

Abstract

This review presents various hole transport layers (HTLs) employed in perovskite solar cells (PSCs) in pursuing high power conversion efficiency (PCE) and functional stability. The PSCs have achieved high PCE (over 23%, certified by NREL) and more efforts have been devoted into research for stability enhancement. Inorganic HTLs become a popular choice as selective contact materials because of their intrinsic chemical stability and low cost. HTLs and electron transport layers (ETLs) are critical components of PSCs due to the requirement to create charge collection selectivity. Herein the authors provide an overview on inorganic HTLs synthesis, properties, and their application in various PSCs for both mesoporous and planar architectures. Inorganic HTLs with appropriate properties, such as proper energy level and high carrier mobility, can not only assist with charge transport, but also improve the stability of PSCs under ambient conditions. The importance of interfacial chemistry and interfacial charge transport is further addressed to understand the underlying mechanism of related degradation and carrier dynamic. It is expected that the success of the inorganic HTL in PSCs can stimulate further research and bring real impact for future photovoltaic technologies.

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.

SrCl₂ is introduced as a co‐precursor in the synthesis of CsPbI₃ perovskite nanocrystals to realize their simultaneous Sr²⁺ cation doping and surface Cl⁻ anion passivation. The stability of the nanocrystals is improved, and light‐emitting devices with a high external quantum efficiency of 13.5% are realized.

Abstract

A method is proposed to improve the photo/electroluminescence efficiency and stability of CsPbI₃ perovskite nanocrystals (NCs) by using SrCl₂ as a co‐precursor. The SrCl₂ is chosen as the dopant to synthesize the CsPbI₃ NCs. Because the ion radius of Sr²⁺ (1.18 Å) is slightly smaller than that of Pb²⁺ (1.19 Å) ions, divalent Sr²⁺ cations can partly replace the Pb²⁺ ions in the lattice structure of perovskite NCs and cause a slight lattice contraction. At the same time, Cl⁻ anions from SrCl₂ are able to efficiently passivate surface defect states of CsPbI₃ nanocrystals, thus converting nonradiative trap states to radiative states. The simultaneous Sr²⁺ ion doping and surface Cl⁻ ion passivation result in the enhanced photoluminescence quantum yield (up to 84%), elongated emission lifetime, and improved stability. Sr²⁺‐doped CsPbI₃ NCs are employed to produce light‐emitting devices with a high external quantum yield of 13.5%.

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.

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.

A quasi‐2D perovskite with high photoluminescence quantum yield and excellent carrier injection efficiency is demonstrated by incorporating n‐butylammonium bromide, CsPbBr₃ and polyethylene oxide. By modulating the optical and electrical properties of quasi‐2D perovskite films, the maximum luminance of PeLEDs is dramatically enhanced from 191 to 33 533 cd m⁻², which is the brightest value yet observed for green quasi‐2D PeLEDs.

Abstract

Quasi‐two‐dimensional (quasi‐2D) perovskites are attracting much attention due to their impressive luminescence properties. However, the introduction of insulating bulky cations reduces the charge transport property of mixed‐dimensional perovskites and leads to lowered brightness and increased turn‐on voltage. The trade‐off between high photoluminescence quantum yield (PLQY) and electrical conductivity should be well manipulated to obtain high‐performance perovskite light‐emitting diodes (PeLEDs). Herein, quasi‐2D perovskite BA₂(CsPbBr₃)_n‐1PbBr₄‐PEO with high PLQY and excellent carrier injection efficiency is demonstrated by incorporating bulky n‐butylammonium bromide (BABr), CsPbBr₃, and polyethylene oxide (PEO). BA can intercalate into the three‐dimensional perovskite framework to form a layered (quasi‐2D) perovskite structure. The ion conductive polymer PEO is used to protect quasi‐2D perovskite crystals. Additional BABr is removed by using anhydrous isopropyl alcohol as a washing agent due to its selective dissolubility. By carefully modulating the optical and electrical properties of quasi‐2D perovskite films, the maximum luminance of PeLEDs is dramatically enhanced from 191 to 33533 cd m⁻², which is the brightest green quasi‐2D PeLED reported thus far, leading to an increase in external quantum efficiency from 1.81% to 8.42%. This work provides a promising route to control the optical and electrical properties of quasi‐2D perovskite films for high‐performance optoelectronic devices.

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.

An effective strategy of promoting grain growth and defects passivation simultaneously for perovskite film by using Ni²⁺ addition is demonstrated. An appreciated efficiency of 20.6% can be achieved for an inverted planar perovskite solar cells device based on a CH₃NH₃PbI₃ (Ni²⁺) film.

Abstract

Today's state‐of‐the‐art perovskite solar cells (PSCs) are utilizing polycrystalline perovskite thin films via solution‐processing at low temperature (<150 °C). It is extremely significant to enlarge grain size and passivate trap states for perovskite thin films to achieve high power conversion efficiency. Herein, a strategy for defect passivation of perovskite films via metal ion Ni²⁺ is for the first time reported. It is found that addition of Ni²⁺ can significantly generate polyporous PbI₂ films due to a different solubility between NiCl₂ and PbI₂ which benefits penetration of MAI and thus formation of large grain perovskite films eventually. It further demonstrated that Ni²⁺ ions can effectively passivate PbI₃ ⁻ antisite defects and restrain the generation of Pb⁰ by interacting with the under‐coordinated halide anions and halide‐rich antisites. Therefore, introducing moderate Ni²⁺ ions result in a significant increase in photoluminescence lifetime from 285 to 732 ns. Accordingly, a power conversion efficiency of 20.61% can be achieved for the 3% Ni²⁺ addition‐based PSCs with an enhanced cell stability under ambient conditions. This work provides a promising route toward perovskite films featuring with high crystallinity and low trap‐density.

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 desirable water–ethanol process is developed for ecofriendly and nonhazardous fabrication of polymer electronic devices. The addition of a typical antisolvent, water, to ethanol remarkably improves the solubility of nonionic oligoethylene glycol side chain‐based electroactive materials, which enables the fabrication of efficient and air‐stable organic field‐effect transistors and polymer solar cells.

Abstract

The authors report the development of a desirable aqueous process for ecofriendly fabrication of efficient and stable organic field‐effect transistors (eco‐OFETs) and polymer solar cells (eco‐PSCs). Intriguingly, the addition of a typical antisolvent, water, to ethanol is found to remarkably enhance the solubility of oligoethylene glycol (OEG) side chain‐based electroactive materials (e.g., the highly crystalline conjugated polymer PPDT2FBT‐A and the fullerene monoadduct PC₆₁BO₁₂). A water–ethanol cosolvent with a 1:1 molar ratio provides an increased solubility of PPDT2FBT‐A from 2.3 to 42.9 mg mL⁻¹ and that of PC₆₁BO₁₂ from 0.3 to 40.5 mg mL⁻¹. Owing to the improved processability, efficient eco‐OFETs with a hole mobility of 2.0 × 10⁻² cm² V⁻¹ s⁻¹ and eco‐PSCs with a power conversion efficiency of 2.05% are successfully fabricated. In addition, the eco‐PSCs fabricated with water–ethanol processing are highly stable under ambient conditions, showing the great potential of this new process for industrial scale application. To better understand the underlying role of water addition, the influence of water addition on the thin‐film morphologies and the performance of the eco‐OFETs and eco‐PSCs are studied. Additionally, it is demonstrated that the application of the aqueous process can be extended to a variety of other OEG‐based material systems.

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.