Ligang Yuan

In article number 1802323, Chih‐Ping Chen and co‐workers demonstrate hydrophilic carbon nanodots efficient additives in perovskite solar cells (PSC). The p‐i‐n PSC device incorporating these additives demonstrated a power conversion efficiency of 20.2% and exhibited excellent air‐stability, maintaining high PCEs (25 °C and a humidity of 40%) for over 500 h.

Charge recombination at grain boundaries is a key factor limiting the performance of low‐bandgap mixed tin–lead halide perovskite solar cells. It is found that bromine incorporation can passivate grain boundaries and lower the dark current density by two to three orders of magnitude. The champion cell shows an open‐circuit voltage deficit of 0.384 V and power conversion efficiency exceeding 19%.

Abstract

The unsatisfactory performance of low‐bandgap mixed tin (Sn)–lead (Pb) halide perovskite subcells has been one of the major obstacles hindering the progress of the power conversion efficiencies (PCEs) of all‐perovskite tandem solar cells. By analyzing dark‐current density and distribution, it is identified that charge recombination at grain boundaries is a key factor limiting the performance of low‐bandgap mixed Sn–Pb halide perovskite subcells. It is further found that bromine (Br) incorporation can effectively passivate grain boundaries and lower the dark current density by two–three orders of magnitude. By optimizing the Br concentration, low‐bandgap (1.272 eV) mixed Sn–Pb halide perovskite solar cells are fabricated with open‐circuit voltage deficits as low as 0.384 V and fill factors as high as 75%. The best‐performing device demonstrates a PCE of >19%. The results suggest an important direction for improving the performance of low‐bandgap mixed Sn–Pb halide perovskite solar cells.

A megasonic spray‐coating system is developed for continuous fabrication of highly uniform, and large‐grain MAPbI₃ films. The large‐area MAPbI₃ layer (56.25 cm²) is coated via a megasonic spray‐coating system and the fabricated solar cells achieve a maximum efficiency of 16.9% with an average efficiency of 16.4% for small active area cells and 14.2% for large active area (1 cm²) cells, respectively.

Abstract

A simple, low‐cost, large area, and continuous scalable coating method is proposed for the fabrication of hybrid organic–inorganic perovskite solar cells. A megasonic spray‐coating method utilizing a 1.7 MHz megasonic nebulizer that could fabricate reproducible large‐area planar efficient perovskite films is developed. The coating method fabricates uniform large‐area perovskite film with large‐sized grain since smaller and narrower sized mist droplets than those generated by existing ultrasonic spray methods could be generated by megasonic spraying. The volume flow rate of the CH₃NH₃PbI₃ precursor solution and the reaction temperature are controlled, to obtain a high quality perovskite active layer. The devices reach a maximum efficiency of 16.9%, with an average efficiency of 16.4% from 21 samples. The applicability of megasonic spray coating to the fabrication of large‐area solar cells (1 cm²), with a power conversion efficiency of 14.2%, is also demonstrated. This is a record high efficiency for large‐area perovskite solar cells fabricated by continuous spray coating.

A series of amino‐functionalized graphene quantum dots (GQDs) with different particle size, small‐GQD, medium‐GQD, and large‐GQD, are prepared for efficient fullerene and nonfullerene organic solar cells. medium‐GQD with medium quantum dot size achieves the balance of interfacial modification ability and conductivity, giving rise to the best device efficiencies both in fullerene and nonfullerene organic solar cells.

Abstract

In this work, a series of amino‐functionalized graphene quantum dots (AF‐GQDs) with different quantum dot sizes are prepared successfully and employed as the cathode interfacial layers (CILs) for fabrication of efficient organic solar cells (OSCs). The effect of quantum dot size on the interfacial modification ability and photovoltaic performance is investigated in detail. By varying the particle size of AF‐GQDs, the work function of the cathode and the conductivity of CIL can be finely tuned. M‐GQD with the medium size achieves the best balance of interfacial modification and conductivity, giving rise to the best power conversion efficiencies both in fullerene and nonfullerene OSCs (poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7):[6,6]‐phenyl‐C₇₁‐butylic acid methyl ester (PC₇₁BM) blend: 10.14%; poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene)‐co‐(1,3‐di(5‐thiophene‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione)] (PBDB‐T):3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC) blend: 11.87%; and poly[(4,8‐bis(5‐(tripropylsilyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene)‐co‐(5,6‐difluoro‐2‐(2‐hexyldecyl)‐4,7‐di(thiophen‐2‐yl)‐2H‐benzo[d][1,2,3]triazole)] (J71):ITIC blend: 12.81%). This work not only provides a new type of high‐performance CIL materials but also demonstrates a simple way for fine‐tuning the interfacial modification ability and the conductivity via just controlling the quantum dot size of AF‐GQDs.

Centimeter‐sized graphene is transferred onto water‐sensitive organometal halide perovskite using a dry method. The graphene–perovskite interface can sustain effective charge transfer and is potentially used as a building block for fabricating multilayer optoelectronic devices.

Abstract

Graphene, a single layer conductor, can be combined with other functional materials for building efficient optoelectronic devices. However, transferring large‐area graphene onto another material often involves dipping the material into water and other solvents. This process is incompatible with water‐sensitive materials such as organometal halide perovskites. Here, a dry method is used and succeeded, for the first time, in stacking centimeter‐sized graphene directly onto methylammonium lead iodide thin films without exposing the perovskite film to any liquid. Photoemission spectroscopy and nanosecond time‐resolved photoelectrical measurement show that the graphene/perovskite interface does not contain significant amount of contaminants and sustain efficient interfacial electron transfer. The use of this method in fabricating graphene‐on‐perovskite photodetectors is further demonstrated. Besides a better photoresponsivity compared to detectors fabricated by the conventional perovskite‐on‐graphene structure, this dry transfer method provides a scalable pathway to incorporate graphene in multilayer devices based on water‐sensitive materials.

Multichannel strategies involving modulation of the counterions, end‐capped substituents, and dimerization are established to regulate the concentrations of azaphenalene diradicals for the first time. The generated anion‐radicals substantially decrease the work functions of the cathode. The all‐solution‐processed bulk heterojunction organic solar cells fabricated with azaphenalene salts based cathode interfacial layers achieve a high power conversion efficiency over 10%.

Abstract

Self‐doped cathode interfacial layers (CILs) are crucial to enable Ohmic‐like contact between the electrode and organic functional layers and thus profoundly promote the performances of organic optoelectronic devices. Herein, multifarious azaphenalene‐embedded organic salts with variable counterions, substituent groups, and repeating units are prepared, and their impacts on producing homologous diradicals are established. Electron paramagnetic resonance and X‐ray photoelectron spectroscopy studies reveal the existence of free radicals of these azaphenalene salts in the solid state. Density functional theory simulations indicate that the thermal energy of counterion‐induced proton transfer is crucial to produce diradicaloids, which can be manipulated in tailoring the azaphenalene backbones. Noticeably, the formed diradicaloids that are delocalized over the π‐conjugated systems will be beneficial to enhance the carrier density of the matrix and remarkably decrease the work functions of the Al electrode. The all‐solution‐processed bulk heterojunction organic solar cells are fabricated by employing them as CILs, which results in high power conversion efficiency of 10.24% in contrast to the 7.34% of the reference device without CILs.

Large‐scaled sheet structured 2D multilayer SnS₂ triggers heterogeneous nucleation over the perovskite precursor film, bringing in balanced electron and hole transport at interfaces between electron transporting layers/perovskite and perovskite/hole transporting layer, and suppressing interfacial charge recombination, achieving the highest 20.12% power conversion efficiency that has so far been reported for perovskite solar cells using a 2D electron transporting layer.

Abstract

Herein, a 2D SnS₂ electron transporting layer is reported via self‐assembly stacking deposition for highly efficient planar perovskite solar cells, achieving over 20% power conversion efficiency under AM 1.5 G 100 mW cm⁻² light illumination. To the best of the authors' knowledge, this represents the highest efficiency that has so far been reported for perovskite solar cells using a 2D electron transporting layer. The large‐scaled 2D multilayer SnS₂ sheet structure triggers a heterogeneous nucleation over the perovskite precursor film. The intermolecular Pb⋅⋅⋅S interactions between perovskite and SnS₂ could passivate the interfacial trap states, which suppress charge recombination and thus facilitate electron extraction for balanced charge transport at interfaces between electron transporting layer/perovskite and hole transporting layer/perovskite. This work demonstrates that 2D materials have great potential for high‐performance perovskite solar cells.

The molecular order of nonfullerene electron acceptor INPIC‐4F is manipulated by varying the self‐organization time during solution casting. With the presence of solvent vapor, INPIC‐4F grows into spherulites with poor efficiency. On the contrary, casting on hot substrates promotes face‐on π−π stacking, which improves absorption as well as efficient exciton dissociation and balanced charge mobility for a maximum efficiency of 13.1%.

Abstract

Developing a fundamental understanding of the molecular order within the photoactive layer, and the influence therein of solution casting conditions, is a key factor in obtaining high power conversation efficiency (PCE) polymer solar cells. Herein, the molecular order in PBDB‐T:INPIC‐4F nonfullerene solar cells is tuned by control of the molecular organization time during film casting, and the crucial role of retarding the crystallization of INPIC‐4F in achieving high performance is demonstrated. When PBDB‐T:INPIC‐4F is cast with the presence of solvent vapor to prolong the organization time, INPIC‐4F molecules form spherulites with a polycrystalline structure, resulting in large phase separation and device efficiency below 10%. On the contrary, casting the film on a hot substrate is effective in suppressing the formation of the polycrystalline structure, and encourages face‐on π−π stacking of INPIC‐4F. This molecular transformation of INPIC‐4F significantly enhances the absorption ability of INPIC‐4F at long wavelengths and facilitates a fine phase separation to support efficient exciton dissociation and balanced charge transport, leading to the achievement of a maximum PCE of 13.1%. This work provides a rational guide for optimizing nonfullerene polymer solar cells consisting of highly crystallizable small molecular electron acceptors.

A high dipole moment cation as a large organic spacer reduces the dielectric confinement effect and hence promotes separation of photogenerated electron–hole pairs in layered 2D perovskite materials, which leads to more efficient and stable perovskite solar cells.

Abstract

Layered 2D organic–inorganic hybrid perovskite is appearing as a rising star in the photovoltaic field, thanks to its superior moisture resistance by the organic spacer cations. Unfortunately, these cations lead to high exciton binding energy in the 2D perovskites, which suffers from lower efficiency in the devices. It thus requires a clear criterion to select/design appropriate organic spacer cations to improve the device efficiency based on this class of materials. Here, 2,2,2‐trifluoroethylamine (F₃EA⁺) is introduced to combine with butylammonium (BA⁺) cations as mixed spacers. While BA⁺ enables self‐assembly of 2D perovskite crystals by van der Waals interaction, the introduction of F₃EA⁺ spacers with a high dipole moment suppress nonradiative recombination and promote separation of photogenerated electron–hole pairs by taking the advantage of electronegativity of fluorine. The resultant solar cells based on [(BA)_{1– x} (F₃EA) _x ]₂(MA)₃Pb₄I₁₃ exhibit substantially increased open circuit voltage and fill factor compared with that of (BA)₂(MA)₃Pb₄I₁₃. The champion [(BA)_0.94(F₃EA)_0.06]₂(MA)₃Pb₄I₁₃ solar cell yields a power conversion efficiency of 12.51%, which is among the best performances so far. These findings suggest an effective strategy to design organic spacer cations in layered perovskite for solar cells and other optoelectronic applications.

A simple, spin‐coating‐free, and directly scalable drop‐cast method is developed to prepare 2D‐perovskite films at arbitrary shapes. The precursor solutions can self‐assemble into highly oriented 2D‐perovskite films on a preheated substrate, producing perovskite solar cells with power conversion efficiencies (PCE) of up to 14.9%, the highest PCE to date for a solar cell with 2D‐perovskite layers fabricated by a nonspin‐coating method.

Abstract

2D organic–inorganic hybrid Ruddlesden–Popper perovskites have emerged recently as candidates for the light‐absorbing layer in solar cell technology due largely to their impressive operational stability compared with their 3D‐perovskite counterparts. The methods reported to date for the preparation of efficient 2D perovksite layers for solar cells involve a nonscalable spin‐coating step. In this work, a facile, spin‐coating‐free, directly scalable drop‐cast method is reported for depositing precursor solutions that self‐assemble into highly oriented, uniform 2D‐perovskite films in air, yielding perovskite solar cells with power conversion efficiencies (PCE) of up to 14.9% (certified PCE of 14.33% ± 0.34 at 0.078 cm²). This is the highest PCE to date for a solar cell with 2D‐perovskite layers fabricated by nonspin‐coating method. The PCEs of the cells display no evidence of degradation after storage in a nitrogen glovebox for more than 5 months. 2D‐perovskite layer deposition using a slot‐die process is also investigated for the first time. Perovskite solar cells fabricated using batch slot‐die coating on a glass substrate or R2R slot‐die coating on a flexible substrate produced PCEs of 12.5% and 8.0%, respectively.

Spectral engineering and ternary blend approaches were employed to demonstrate an efficient semitransparent polymer solar cell tailored for greenhouse application. The semitransparent device transmits mainly blue and red lights for photosynthesis, and shows a high efficiency of 7.75% with a crop growth factor of 24.8%. Optimal sunlight harvesting in photovoltaics and photosynthesis will be beneficial for future greenhouse application.

Abstract

In this study, a wavelength selective semitransparent polymer solar cell (ST‐PSC) with a proper transmission spectrum for plant growth is proposed for greenhouse applications. A ternary strategy combining a wide bandgap polymer donor with a near‐infrared absorbing nonfullerene acceptor and a high electron mobility fullerene acceptor is introduced to achieve PSCs with power conversion efficiency (PCE) over 10%. The addition of PC₇₁BM into J52:IEICO‐4F binary blend contributes to the suppressed trap‐assisted recombination, enhanced charge extraction, and improved open‐circuit voltage simultaneously. ST‐PSC based on the J52:IEICO‐4F:PC₇₁BM ternary blend shows an optimized performance with PCE of 7.75% and a defined crop growth factor of 24.8%. Such high‐performance ST‐PSC is achieved by carefully engineering the absorption spectrum of the light harvesting materials. As a result, the transmission spectra of the semitransparent devices are well‐matched with the absorption spectra of the photoreceptors, such as chlorophylls, in green plants, which provides adequate lighting conditions for photosynthesis and plant growth, and therefore making it a competitive candidate for photovoltaic greenhouse applications.

To finely tune blend miscibility, a novel chemical tool of steric engineering is proposed. It renders a high PCE over 12% for the polymer with middle steric structure, due to a more balanced blend miscibility without sacrificing charge‐carrier transport. Therefore the steric effect‐induced miscibility (SEIM) as a novel chemical strategy exhibits very simple and promising potential in optimizing morphology.

Abstract

Morphology and miscibility control are still a great challenge in polymer solar cells. Despite physical tools being applied, chemical strategies are still limited and complex. To finely tune blend miscibility to obtain optimized morphology, chemical steric engineering is proposed to systemically investigate its effects on optical and electronic properties, especially on a balance between crystallinity and miscibility. By changing the alkylthiol side chain orientation different steric effects are realized in three different polymers. Surprisingly, the photovoltaic device of the polymerPTBB‐m with middle steric structure affords a better power conversion efficiency, over 12%, compared to those of the polymers PTBB‐o and PTBB‐p with large or small steric structures, which could be attributed to a more balanced blend miscibility without sacrificing charge‐carrier transport. Space charge‐limited current, atomic force microscopy, grazing incidence wide angle X‐ray scattering, and resonant soft X‐ray scattering measurements show that the steric engineering of alkylthiol side chains can have significant impacts on polymer aggregation properties, blend miscibility, and photovoltaic performances. More important, the control of miscibility via the simple chemical approach has preliminarily proved its great potential and will pave a new avenue for optimizing the blend morphology.

Two new copper (II) phthalocyanine (CuPc) derivatives, namely CuPc‐Bu and CuPc‐OBu, are designed by molecular engineering of the non‐peripheral substituents of the Pc rings, and are further explored as dopant‐free hole‐transporting materials (HTMs) in perovskite solar cells (PSCs). The PSCs based on pristine CuPc‐OBu as HTMs afford a maximum power conversion efficiency of 17.6%, which is considerably higher than that of the devices with CuPc‐Bu (14.3%).

Abstract

Copper (II) phthalocyanines (CuPcs) have attracted growing interest as promising hole‐transporting materials (HTMs) in perovskite solar cells (PSCs) due to their low‐cost and excellent stability. However, the most efficient PSCs using CuPc‐based HTMs reported thus far still rely on hygroscopic p‐type dopants, which notoriously deteriorate device stability. Herein, two new CuPc derivatives are designed, namely CuPc‐Bu and CuPc‐OBu, by molecular engineering of the non‐peripheral substituents of the Pc rings, and applied as dopant‐free HTMs in PSCs. Remarkably, a small structural change from butyl groups to butoxy groups in the substituents of the Pc rings significantly influences the molecular ordering and effectively improves the hole mobility and solar cell performance. As a consequence, PSCs based on dopant‐free CuPc‐OBu as HTMs deliver an impressive power conversion efficiency (PCE) of up to 17.6% under one sun illumination, which is considerably higher than that of devices with CuPc‐Bu (14.3%). Moreover, PSCs containing dopant‐free CuPc‐OBu HTMs show a markedly improved ambient stability when stored without encapsulation under ambient conditions with a relative humidity of 85% compared to devices containing doped Spiro‐OMeTAD. This work thus provides a fundamental strategy for the future design of cost‐effective and stable HTMs for PSCs and other optoelectronic devices.

Large‐scale flexible photodetector arrays are fabricated based on patterned CH₃NH₃PbI_{3− x} Cl _x film. In addition, the device, with outstanding optoelectronic performance and excellent electrical stability, is applied to capture a real‐time light trajectory and detect a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, imaging, and artificial electronic skin applications.

Abstract

The quest for novel deformable image sensors with outstanding optoelectronic properties and large‐scale integration becomes a great impetus to exploit more advanced flexible photodetector (PD) arrays. Here, 10 × 10 flexible PD arrays with a resolution of 63.5 dpi are demonstrated based on as‐prepared perovskite arrays for photosensing and imaging. Large‐scale growth controllable CH₃NH₃PbI_{3− x} Cl _x arrays are synthesized on a poly(ethylene terephthalate) substrate by using a two‐step sequential deposition method with the developed Al₂O₃‐assisted hydrophilic–hydrophobic surface treatment process. The flexible PD arrays with high detectivity (9.4 × 10¹¹ Jones), large on/off current ratio (up to 1.2 × 10³), and broad spectral response exhibit excellent electrical stability under large bending angle (θ = 150°) and superior folding endurance after hundreds of bending cycles. In addition, the device can execute the functions of capturing a real‐time light trajectory and detecting a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, digital display, and artificial electronic skin applications.

Mixed lead–tin perovskites are shown to be efficient near‐infrared light emitters with tunable emission wavelengths from 850 to 950 nm. Devices based on MAPb_0.6Sn_0.4I₃ films with 4‐fluorobenzylammonium iodide additives reach external quantum efficiency of 5%. It is revealed that there is no phase separation during the operation of devices with various Pb:Sn ratios and different mixed iodide and bromide compositions.

Abstract

Near‐infrared (NIR) light‐emitting diodes (LEDs), with emission wavelengths between 800 and 950 nm, are useful for various applications, e.g., night‐vision devices, optical communication, and medical treatments. Yet, devices using thin film materials like organic semiconductors and lead based colloidal quantum dots face certain fundamental challenges that limit the improvement of external quantum efficiency (EQE), making the search of alternative NIR emitters important for the community. In this work, efficient NIR LEDs with tunable emission from 850 to 950 nm, using lead–tin (Pb‐Sn) halide perovskite as emitters are demonstrated. The best performing device exhibits an EQE of 5.0% with a peak emission wavelength of 917 nm, a turn‐on voltage of 1.65 V, and a radiance of 2.7 W Sr⁻¹ m⁻² when driven at 4.5 V. The emission spectra of mixed Pb‐Sn perovskites are tuned either by changing the Pb:Sn ratio or by incorporating bromide, and notably exhibit no phase separation during device operation. The work demonstrates that mixed Pb‐Sn perovskites are promising next generation NIR emitters.

The atomic structure and electronic properties of Ruddlesden–Popper (RP) faults and grain boundaries (GBs) in CsPbBr₃ are revealed using electron microscopy and density functional theory calculations. The halide concentration at these planar defects is found to be crucial to their electronic properties. The GBs are predicted to repel electrons and attract holes, whereas the RP faults repel both.

Abstract

To evaluate the role of planar defects in lead‐halide perovskites—cheap, versatile semiconducting materials—it is critical to examine their structure, including defects, at the atomic scale and develop a detailed understanding of their impact on electronic properties. In this study, postsynthesis nanocrystal fusion, aberration‐corrected scanning transmission electron microscopy, and first‐principles calculations are combined to study the nature of different planar defects formed in CsPbBr₃ nanocrystals. Two types of prevalent planar defects from atomic resolution imaging are observed: previously unreported Br‐rich [001](210)∑5 grain boundaries (GBs) and Ruddlesden–Popper (RP) planar faults. The first‐principles calculations reveal that neither of these planar faults induce deep defect levels, but their Br‐deficient counterparts do. It is found that the ∑5 GB repels electrons and attracts holes, similar to an n–p–n junction, and the RP planar defects repel both electrons and holes, similar to a semiconductor–insulator–semiconductor junction. Finally, the potential applications of these findings and their implications to understand the planar defects in organic–inorganic lead‐halide perovskites that have led to solar cells with extremely high photoconversion efficiencies are discussed.

The rapid development in large‐area organic solar cells (OSCs) is reviewed. Materials requirements, modular designs, and printing methods for large‐area OSCs are discussed. By combining thick‐film material systems with efficient modular designs, and then by employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.

Abstract

The printing of large‐area organic solar cells (OSCs) has become a frontier for organic electronics and is also regarded as a critical step in their industrial applications. With the rapid progress in the field of OSCs, the highest power conversion efficiency (PCE) for small‐area devices is approaching 15%, whereas the PCE for large‐area devices has also surpassed 10% in a single cell with an area of ≈1 cm². Here, the progress of this fast developing area is reviewed, mainly focusing on: 1) material requirements (materials that are able to form efficient thick active layer films for large‐area printing); 2) modular designs (effective designs that can suppress electrical, geometric, optical, and additional losses, leading to a reduction in the PCE of the devices, as a consequence of substrate area expansion); and 3) printing methods (various scalable fabrication techniques that are employed for large‐area fabrication, including knife coating, slot‐die coating, screen printing, inkjet printing, gravure printing, flexographic printing, pad printing, and brush coating). By combining thick‐film material systems with efficient modular designs exhibiting low‐efficiency losses and employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.

Efficient two-terminal all-perovskite tandem solar cells enabled by high-quality low-bandgap absorber layers

Efficient two-terminal all-perovskite tandem solar cells enabled by high-quality low-bandgap absorber layers, Published online: 26 November 2018; doi:10.1038/s41560-018-0278-x

Two-terminal monolithic all-perovskite tandem solar cells are attractive due to their flexible nature and low-cost fabrication. Here the authors develop a process to obtain high-quality Sn–Pb perovskite thin films by incorporating chlorine. Such layers are employed to fabricate 20.7%-efficient tandem cells with 80 h operational stability.

An n‐doped organic‐inorganic hybrid perovskite film is realized directly incorporating AgI into the CH₃NH₃PbI₃ precursor solution. AgI doping resulted in a remarkable increase in the electron mobility by the aligned orientation of MA⁺ ions owing to the Ag⁺‐influenced distribution of the electron cloud density. Consequently, a stable perovskite solar cell with a power conversion efficiency of 20.02% is obtained.

The disparity of hole and electron behavior is a ubiquitous issue in methylammonium lead halide perovskites. The carrier mobility imbalance, which will result in a built‐in electric field thus increase the device resistance, is regarded as one of main limiting factors for the further improvement of device performance in perovskite solar cells (PSCs). Here, we realized an n‐doped organic‐inorganic hybrid perovskite by directly incorporating AgI into the CH₃NH₃PbI₃ precursor solution, to fabricate high‐performance PSCs. AgI doping resulted in a balanced charge transporting owing to a remarkable increase in the electron mobility, which was attributed to the aligned orientation of MA⁺ ions owing to the Ag⁺‐influenced distribution of electron cloud density. Meanwhile, AgI could act as an additive to control the perovskite crystallization with improved crystallinity and film morphology. Consequently, a maximum power conversion efficiency of over 20% is achieved. The finding in this work provides a direction to fabricate high‐performance PSCs by controlling the charge balance via intensive doping technique.

Br induced room temperature crystallization of highly photoactive black phase FA‐based perovskite films with high performance and reproducibility is reported. The halide Br/I formulation are 0.2/2.8 and 0.5/2.5 for room‐temperature perovskite crystallization at 35–40 °C and 20–25 °C, yielding solar to electric conversion efficiency of 19.59 and 17.53% with high reproducibility, respectively.

State‐of‐the art perovskite solar cells (PSCs) are obtained by using a high‐crystalline and uniform morphological perovskite film that usually requires a thermal procedure to induce its crystallization. Room temperature processing photoactive perovskite film represents a feasible approach to break through the technology barrier arising from high temperature annealing procedures; however, the photovoltaic performance of fabricated PSCs varies significantly in most routine laboratories with ambient temperature altering. Herein, the authors report for the first time that highly photoactive black phase FA‐based perovskite films with high performance and reproducibility can be room temperature processed via the Br induced crystallization effect. It is found that Br adding content varies as a function of ambient temperature fluctuation from 35–40 to 20–25 °C. The halide Br/I formulation are 0.2/2.8 and 0.5/2.5 for room‐temperature perovskite crystallization in ambient temperatures of 35–40 and 20‐25 °C, yieldings solar to electric power conversion efficiency of 19.59 and 17.53% with high reproducibility, respectively. This efficiency (19.59%) is comparable to the best‐performing PSCs based on thermal processing perovskite films. This work provides a valuable and practical guide to room‐temperature fabrication of PSCs with high efficiency and reproducibility by delicate control of halide anions.

In article no. 1800217, Mingzhen Liu and co‐workers fabricate a Cs₂Ag‐BiBr₆ double perovskite film that is potentially desirable for lead‐free solar cell applications. The films exhibit high quality in terms of large compact grains, high uniformity, and long‐term stability.

In article no. 1800177, Zhi Yang, Minqiang Wang, and Jinjuan Dou discuss interface engineering in n‐i‐p metal halide perovskite solar cells, achieved by introducing 2D perovskites, functional molecules, quantum dots, and an insulating layer, which allows for better energy‐level alignment, passivating traps, resisting moisture, and suppressing ion migration. This contributes to improved performance, enhanced long‐term stability, and eliminated photocurrent hysteresis.