JIALINGBO

A novel bifunctional (anti)solvent system is developed for regulating the perovskite crystallization procedure. It can perform not only as an antisolvent at the spin‐coating step to rapidly generate crystal seeds, but also as a solvent for ripening the precursors to large crystal grains during the thermal‐annealing process. Therefore, it can significantly enhance the efficiency, stability, and reproducibility of perovskite solar cells.

Abstract

The preparation of high‐quality perovskite films is important for achieving high‐performance perovskite solar cells (PSCs). The effective balance between solvent and antisolvent is an essential factor for regulating high‐quality perovskite film during the spin‐coating and thermal‐annealing steps. In this work, a greener, nonhalogenated, nontoxic bifunctional (anti)solvent, methyl benzoate (MB), is developed not only as an antisolvent to rapidly generate crystal seeds at the perovskite spin‐coating step, but also as a digestive‐ripening solvent for the perovskite precursors, which can prevent the loss of organic components during the thermal‐annealing stage and effectively suppress the formation of miscellaneous lead halide phases. As a result, this novel bifunctional (anti)solvent is employed in planar n–i–p PSCs for engineering high‐quality perovskite layers and thus achieving a power conversion efficiency up to 22.37% with negligible hysteresis and >1300 h stability. Moreover, due to the high boiling point and low‐volatility characteristic of MB, high‐performance PSCs are achieved reproducibly at different operating temperatures (22–34 °C). Therefore, this developed bifunctional solvent system can provide a promising platform toward globally upscaling and commercializing PSCs in all seasons and regions.

In article https://doi.org/10.1002/aenm.2019033261903326, Prashant Sonar and co‐workers review the state‐of‐the‐art for dopant‐free organic hole transporting materials (HTMs) in perovskite solar cells. Depicted, are different device architectures using the small molecular HTM, ACE‐QA‐ACE, which has shown enhanced stability over doped HTMs.

One‐dimensional (1D) nanostructured oxides have been proposed as excellent electron transport materials (ETMs) for perovskite solar cells (PSCs), but this has not yet been demonstrated experimentally. Here, we exploit a facile hydrothermal approach to grow highly oriented anatase TiO2 nanopyramid arrays and further demonstrate their advantages for application in PSCs. The oriented TiO2 nanopyramid arrays afford sufficient contact area for electron extraction and increase light transmission. Moreover, the nanopyramid array/perovskite system exhibits an oriented electric field that can increase charge separation and accelerate charge transport, thereby suppressing charge recombination. As a result, the anatase TiO2 nanopyramid arrays‐PSCs deliver a champion power conversion efficiency of ~22.5%, which is the highest PCE reported thus far for PSCs consisting of 1D ETMs. This work demonstrates that the rational design of 1D ETMs can achieve PSCs that perform as well as typical mesoscopic and planar PSCs.

A new strategy is established to improve the performance of perovskite solar cells, which sheds more light on the currently proposed mechanism governing the action of moisture on the quality of perovskite film. Self‐passivated perovskite solar cells show an extraordinary V_OC of 1.17 V and the highest efficiency of 21.38%.

The performance of perovskite solar cells (PSCs) is known to be extremely sensitive to humidity in the preparation environment. However, the main mechanism by which the moisture influences the quality of the perovskite film and the device performance is not yet fully understood. Herein, a new strategy is established to obtain inverted PSCs with a remarkabll high V _OC by including a high‐humidity treatment and sufficient DMSO‐atmosphere annealing in the preparation process. It is found that the lattice distortion on the surface of perovskite grains caused by the high‐humidity treatment plays a key role in the self‐passivation of perovskite. Inverted (p‐i‐n) PSCs based on the self‐passivated perovskite films show effective suppression of nonradiative recombination, which increase the device V _OC to 1.17 V and achieve the highest efficiency of 21.38%. It is expected that the findings of this work shed more light on the currently proposed mechanism governing the action of moisture on the performance of the PSCs.

The A‐site incorporation in the all‐inorganic cesium lead mixed halide (CsPbI₂Br) perovskite facilitates thermodynamic stability. The Rb cation‐incorporated Cs_1−x M _x PbI₂Br (M = Rb)‐based perovskite absorber layer processed by hot air method under ambient conditions with additives doped poly(3‐hexylthiophene‐2,5‐diyl) as a hole‐transporting layer produces a power conversion efficiency of more than 17%.

Due to its excellent thermal stability and high performance, inorganic cesium lead mixed halide (ABX₃, where A  = Cs, B = Pb, and X = I/Br) all‐inorganic perovskite solar cells (IPVSCs) have attracted much interest in optoelectronic applications. However, the film quality, enough absorption by desired film thickness, and nature of partial replacement of cations determine the stability of the CsPbI₂Br perovskite films. Herein, a hot air method is used to control the thickness and morphology of the CsPbI₂Br perovskite thin film, and the A‐site (herein, Cs⁺) cation is partially incorporated by rubidium (Rb⁺) cations for making the stable black phase under ambient conditions. The Rb cation‐incorporated Cs_1−x Rb _x PbI₂Br (x  = 0–0.03) perovskite thin films exhibit high crystallinity, uniform grains, extremely dense, and pinhole‐free morphology. The fabricated device with its Cs_0.99Rb_0.01PbI₂Br perovskite composition with poly(3‐hexylthiophene‐2,5‐diyl) as a hole‐transporting layer exhibits a power conversion efficiency (PCE) of 17.16%, which is much higher than that of CsPbI₂Br‐based IPVSCs. The fabricated Cs_0.99Rb_0.01PbI₂Br‐based IPVSC devices retain >90% of the initial efficiency over 120 h at 65 °C thermal stress, which is much higher than that of CsPbI₂Br samples.

Metal oxides (MO) with unique optoelectronic properties and outstanding stability are increasingly developed as effective electron transport layers (ETLs) for perovskite solar cells (PSCs). This Review focuses on the recent advances of MO ETLs from systematical synthesis to strategical optimization and provides feasible directions for future development of MO ETLs in higher‐performing PSCs.

Abstract

Organometallic mixed halide perovskite solar cells (PSCs) have emerged as a promising photovoltaic technology with increasingly improved device efficiency exceeding 24%. Charge transport layers, especially electron transport layers (ETLs), are verified to play a vital role in device performance and stability. Recently, metal oxides (MOs) have been widely studied as ETLs for high‐performance PSCs due to their excellent electronic properties, superb versatility, and great stability. This Review briefly discusses the development of PSCs' architecture and outlines the requirements for MO ETLs. Additionally, recent progress of MO ETLs from preparation to optimization for efficient PSCs is systematically summarized and highlighted to associate the versatility of MO ETLs with the performance of devices. Finally, a summary and prospectives for the future development of MO ETLs toward practical application of high‐performance PSCs are drawn.

A C₃N₃ is prepared in large scale from cheap cyanuric chloride on copper surface under nonvacuum conditions. It has good photoelectrochemical activity for water splitting and can be exfoliated to 2D polymeric films. This work not only enlarges the family of polymeric carbon nitrides, but also opens the door for synthesizing 2D conjugated polymers based on Ullmann polymerization.

Abstract

Polymeric carbon nitride (PCN) has been extensively researched in recent years. This research has mainly focussed on C₃N₄ because types of PCN are quite limited and other types are not easily synthesized. Therefore developing new types of easily‐synthesized PCN beyond C₃N₄ offers new opportunities. C₃N₃ has been predicted but it has not been successfully synthesized before. Herein it is prepared in large scale from cheap cyanuric chloride on a copper surface under nonvacuum conditions. The C₃N₃ has a good photoelectrochemical (PEC) activity for water splitting and can be exfoliated to 2D polymeric films. This breakthrough work not only enlarges the family of PCN, but also opens the door for large‐scale synthesis of other similar C–C bonded 2D conjugated polymers based on Ullmann polymerization. Similar to graphene and C₃N₄, follow‐up research related to this C₃N₃ in different fields may emerge in the near future.

Flexible‐solution processed photodetectors with a vertical device structure incorporating a CH₃NH₃PbI₃/PbSe quantum dot bilayer on polymeric thin film are demonstrated. They exhibit a spectral response ranging from 300 nm to 2600 nm, photodetectivity of over 10¹¹ cm Hz^1/2 W⁻¹, and linear dynamic range of 70 dB.

Abstract

Room‐temperature solution‐processed flexible photodetectors with spectral response from 300 to 2600 nm are reported. Solution‐processed polymeric thin film with transparency ranging from 300 to 7000 nm and superior electrical conductivity as the transparent electrode is reported. Solution‐processed flexible broadband photodetectors with a “vertical” device structure incorporating a perovskite/PbSe quantum dot bilayer thin film based on the above solution‐processed transparent polymeric electrode are demonstrated. The utilization of perovskite/PbSe quantum dot bilayer thin film as the photoactive layer extends spectral response to infrared region and boosts photocurrent densities in both visible and infrared regions through the trap‐assisted photomultiplication effect. Operated at room temperature and under an external bias of ‐1 V, the solution‐processed flexible photodetectors exhibit over 230 mA W^‐1 responsivity, over 1011 cm Hz1/2/W photodetectivity from 300 to 2600 nm and ≈70 dB linear dynamic ranges. It is also found that the solution‐processed flexible broadband photodetectors exhibit fast response time and excellent flexibility. All these results demonstrate that this work develop a facile approach to realize room‐temperature operated ultrasensitive solution‐processed flexible broadband photodetectors with “vertical” device structure through solution‐processed transparent polymeric electrode.

A strong fluorine‐containing Lewis acid tris(pentafluorophenyl) phosphine (TPFP) is developed to passivate mixed perovskite solar cells, achieving a champion efficiency of 22.02% and a high stability under 85% relative humidity. The moisture degradation mechanism is phase segregation of I‐rich black phase and Cs/Br‐rich yellow phase resulting from water‐assisted synergistic Cs and halide ion migrations.

Abstract

Multiple‐cation lead mixed‐halide perovskites (MLMPs) have been recognized as ideal candidates in perovskite solar cells in terms of high efficiency and stability due to decreased open‐circuit voltage loss and suppressed yellow phase formation. However, they still suffer from an unsatisfactory long‐term moisture stability. In this study, phosphorus‐containing Lewis acid and base molecules are employed to improve device efficiency and stability based on their multifunction including recombination reduction, phase segregation suppression, and moisture resistance. The strong fluorine‐containing Lewis acid treatment can achieve a champion PCE of 22.02%. Unencapsulated and encapsulated devices retain 63% and 80% of the initial efficiency after 14 days of aging under 75% and 85% relative humidity, respectively. The better passivation of Lewis acid implies more halide defects than Pb defects at the MLMP surface. This unbalanced defect type results from phase segregation that is the synergistic effect of Cs and halide ion migrations. Identifying defect type based on different passivation effects is beneficial to not only choose suitable passivators to boost the efficiency and slow down the moisture degradation of MLMP solar cells, but also to understand the mechanism of defect‐assisted moisture degradation.

Graphitic carbon nitride (g‐C₃N₄) is doped into PEDOT:PSS to improve the conductivity by weakening the shield effect of PSS on conductive PEDOT. Employing g‐C₃N₄ doped PEDOT:PSS as a hole transport layer for PM6:Y6‐based organic solar cells, a device efficiency of up to 16.4% is achieved, partly as a result of improved charge transport and suppressed charge recombination at the interface.

Abstract

The power‐conversion efficiency (PCE) of single‐junction organic solar cells (OSCs) has exceeded 16% thanks to the development of non‐fullerene acceptor materials and morphological optimization of active layer. In addition, interfacial engineering always plays a crucial role in further improving the performance of OSCs based on a well‐established active‐layer system. Doping of graphitic carbon nitride (g‐C₃N₄) into poly(3,4‐ethylene‐dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer (HTL) for PM6:Y6‐based OSCs is reported, boosting the PCE to almost 16.4%. After being added into the PEDOT:PSS, the g‐C₃N₄ as a Bronsted base can be protonated, weakening the shield effect of insulating PSS on conductive PEDOT, which enables exposures of more PEDOT chains on the surface of PEDOT:PSS core‐shell structure, and thus increasing the conductivity. Therefore, at the interface between g‐C₃N₄ doped HTL and PM6:Y6 layer, the charge transport is improved and the charge recombination is suppressed, leading to the increases of fill factor and short‐circuit current density of devices. This work demonstrates that doping g‐C₃N₄ into PEDOT:PSS is an efficient strategy to increase the conductivity of HTL, resulting in higher OSC performance.

By employing HOOCCH₂NH₃ ⁺ (Gly⁺) with its outstanding additive effect, self‐additive low‐dimensional Ruddlesden–Popper perovskites are first designed. As a result, the Gly‐based self‐additive low‐dimensional RP perovskites with large grain sizes exhibit remarkable photoelectric properties, yielding the highest power conversion efficiency of 18.06% with negligible hysteresis. More importantly, Gly‐based devices exhibit markedly improved stability against humidity, heat, and UV light.

Abstract

The recent rise of low‐dimensional Ruddlesden–Popper (RP) perovskites is notable for superior humidity stability, however they suffer from low power conversion efficiency (PCE). Suitable organic spacer cations with special properties display a critical effect on the performance and stability of perovskite solar cells (PSCs). Herein, a new strategy of designing self‐additive low‐dimensional RP perovskites is first proposed by employing a glycine salt (Gly⁺) with outstanding additive effect to improve the photovoltaic performance. Due to the strong interaction between CO and Pb²⁺, the Gly⁺ can become a nucleation center and be beneficial to uniform and fast growth of the Gly‐based RP perovskites with larger grain sizes, leading to reduced grain boundary and increased carrier transport. As a result, the Gly‐based self‐additive low‐dimensional RP perovskites exhibit remarkable photoelectric properties, yielding the highest PCE of 18.06% for Gly (n = 8) devices and 15.61% for Gly (n = 4) devices with negligible hysteresis. Furthermore, the Gly‐based devices without encapsulation show excellent long‐term stability against humidity, heat, and UV light in comparison to BA‐based low‐dimensional PSCs. This approach provides a feasible design strategy of new‐type low‐dimensional RP perovskites to obtain highly efficient and stable devices for next‐generation photovoltaic applications.

A malonic acid‐decorated fullerene (MA‐C₆₀) with superoxide dismutase activity and water scavenging capability is used as an effective electrolyte additive to enhance the interfacial stability of high‐capacity electrodes.

Abstract

High‐capacity Li‐rich layered oxide cathodes along with Si‐incorporated graphite anodes have high reversible capacity, outperforming the electrode materials used in existing commercial products. Hence, they are potential candidates for the development of high‐energy‐density lithium‐ion batteries (LIBs). However, structural degradation induced by loss of interfacial stability is a roadblock to their practical use. Here, the use of malonic acid‐decorated fullerene (MA‐C₆₀) with superoxide dismutase activity and water scavenging capability as an electrolyte additive to overcome the structural instability of high‐capacity electrodes that hampers the battery quality is reported. Deactivation of PF₅ by water scavenging leads to the long‐term stability of the interfacial structures of electrodes. Moreover, an MA‐C₆₀‐added electrolyte deactivates the reactive oxygen species and constructs an electrochemically robust cathode‐electrolyte interface for Li‐rich cathodes. This work paves the way for new possibilities in the design of electrolyte additives by eliminating undesirable reactive substances and tuning the interfacial structures of high‐capacity electrodes in LIBs.

Novel fullerene dimers are designed and employed as interfacial materials in perovskite solar cells, and shown to be effective at passivating and stabilizing devices with a maximum efficiency of 22.3% without any hysteresis and with 98% retained efficiency after ambient storage for 1000 h.

Abstract

A major limit for planar perovskite solar cells is the trap‐mediated hysteresis and instability, due to the defective metal oxide interface with the perovskite layer. Passivation engineering with fullerenes has been identified as an effective approach to modify this interface. The rational design of fullerene molecules with exceptional electrical properties and versatile chemical moieties for targeted defect passivation is therefore highly demanded. In this work, novel fulleropyrrolidine (NMBF‐X, XH or Cl) monomers and dimers are synthesized and incorporated between metal oxides (i.e. TiO₂, SnO₂) and perovskites (i.e. MAPbI₃ and (FAPbI₃) _x (MAPbBr₃)_{1‐ x} ). The fullerene dimers provide superior stability and efficiency improvements compared to the corresponding monomers, with chlorinated fullerene dimers being most effective at coordinating with both metal oxides and perovskite via the chlorine terminals. The non‐encapsulated planar device delivers a maximum power conversion efficiency of 22.3% without any hysteresis, while maintaining over 98% of initial efficiency after ambient storage for 1000 h, and exhibiting an order of magnitude improvement of the T₈₀ lifetime.

An oxidized phenothiazine‐based (OPTZ) hole transporting material (HTM) synthesized from its neutral form (NPTZ) is used to accurately tune the concentration of radical cations in HTMs via its stoichiometric ratio. Using the optimized ratio of OPTZ as the dopant in the HTM, the hole transporting mobility is effectively enhanced, due to the intra‐and intermolecular charge transfer process, thus increasing the fill‐factor of perovskite solar cells.

In traditional n‐i‐p‐type perovskite solar cells (PSCs), most hole transporting materials (HTMs) rely on an uncontrolled oxidative process using Li salt and Co (III) complex to achieve sufficient hole mobilities. Herein, a stabilized oxidized phenothiazine‐based HTM (OPTZ) synthesized from its neutral form (NPTZ) through a photoredox reaction is demonstrated. This controllable and stable oxidation state is mainly derived from the planar structure and π conjugation of phenothiazine core in OPTZ. The energy gap between the singly occupied molecular orbital (SOMO) of OPTZ and highest occupied molecular orbital (HOMO) of NPTZ suitably promotes hole hopping in hole transporting layers. Using an optimized ratio of OPTZ as the dopant in NPTZ, the hole transporting mobility is effectively enhanced due to an intra‐ and intermolecular charge transfer process, resulting in an enhancement in the fill factor of the PSCs. Herein, a new strategy to obtain stabilized oxidized HTMs, which deliver significantly enhanced hole mobilities of HTMs in PSCs, is provided.

Herein, an antireflective cascaded SnO₂/TiO₂–Cl electron transport layer is devised to reduce the primary optical reflection of planar perovskite solar cells (PSCs) at the front side. A record‐high short‐circuit current density of 26.1 mA cm⁻² and a high power conversion efficiency of 22.9% are achieved in FAPbI₃‐based planar PSCs.

Planar perovskite solar cells (PSCs) hold promise for simple processing at low temperatures; however, they usually show lower short‐circuit current density (J _sc) than their mesoporous counterparts owing to their higher primary optical reflection losses at the front side. The antireflective nature of a mesoporous electron transport layer (ETL) enables a low optical reflection in the front surface of solar cells, which is challenging to realize in planar PSCs. Herein, an antireflective cascaded ETL structure using SnO₂/TiO₂–Cl bilayers is devised to reduce optical reflection losses and to improve electrical performance in planar PSCs. The antireflective cascaded ETL results in an enhanced J _sc of 25.4 mA cm⁻² in formamidinium lead triiodide based planar PSCs, compared with the control J _sc of 24.6 mA cm⁻² using single‐layered SnO₂ ETL. A record‐high J _sc of 26.1 mA cm⁻² is further achieved using an additional antireflective coating on the front glass side, leading to a power conversion efficiency of 22.9%.

By varying thermal annealing conditions, a thermally induced perovskite crystal control process of the wide‐bandgap perovskite films provides an opportunity to exploit both lead‐iodide passivation and perovskite orientation strategies with a fixed E _g of 1.73 eV. Based on this concept, the device efficiency is improved from 15.76% to 18.60% and the operational photostability is also enhanced without any encapsulation in ambient conditions.

Wide‐bandgap perovskite solar cells (WBG PSCs) have gained attention as promising tandem partners for silicon solar cells due to their complementary absorption, superb open‐circuit voltage, and an easy solution process. Recently, both their performance and stability have been improved by compositional engineering or defect passivation strategies, due to the modulation of perovskite crystal size and reduction of crystal defects. Herein, a report on the thermally induced phase control (TIPC) strategy is provided, which enables efficient and photostable WBG PSCs without compositional engineering by exploring a thermal annealing process window (100–175 °C and 3–60 min) of the WBG perovskite films. Within this window, a key annealing regime is found that produces preferred crystal orientations of lead iodide and the WBG perovskite, suppressing phase segregation and reducing charge recombination in the perovskites. The WBG PSCs (composition of FA_0.75MA_0.15Cs_0.1PbI₂Br and E _g of 1.73 eV) optimized by TIPC exhibit an excellent power conversion efficiency (PCE) of 18.60% and improved operational stability, maintaining >90% of the maximum PCE (during maximum power point tracking) without encapsulation after 12 h of operation (air mass 1.5 global irradiation in ambient air conditions) or after 500 h of operation (white light‐emitting diode irradiation (100 mW cm⁻²) in N₂ conditions).

Against the grain: Adding melamine maximizes grain size and minimizes defects in CsPbBr₃ perovskite films. The resulting CsPbBr₃ perovskite solar cell (PSC) free of encapsulation achieves a champion power conversion efficiency (PCE) of 9.65 % and excellent thermal and humidity stability.

Abstract

The preparation of high‐quality perovskite films with low grain boundaries and defect states is a prerequisite for achieving high‐efficiency perovskite solar cells (PSCs) with good environmental stability. An effective additive engineering strategy has been developed for simultaneous defect passivation and crystal growth of CsPbBr₃ perovskite films by introducing 1,3,5‐triazine‐2,4,6‐triamine (melamine) into the PbBr₂ precursor solution. The resultant melamine–PbBr₂ film has a loose, large‐grained structure and decreased crystallinity, which has a positive effect on the crystallization process of the perovskite as it retards the crystallization rate as a result of the interaction between melamine and lead ions. Additionally, the passivation by melamine gives a high‐quality CsPbBr₃ perovskite film with fewer grain boundaries, lower defect densities, and better energy level matching is achieved by multistep liquid‐phase spin‐coating, which greatly suppresses the nonradiative recombination resulting from the defects and promotes charge extraction at the interface. A champion power conversion efficiency as high as 9.65 % with a promising open‐circuit voltage of 1.584 V is achieved for PSCs with an architecture of fluorine‐doped tin oxide/c‐TiO₂/m‐TiO₂/melamine‐added CsPbBr₃/carbon‐based hole‐transporting layer. Furthermore, the unencapsulated melamine‐added CsPbBr₃ PSC shows superior thermal and humidity stability in ambient air at 85 °C or 85 % relative humidity over 720 h.

A nonhalogen organic salt sodium p‐toluenesulfonate (STS) is applied during the surface modification of perovskite films for the first time, yielding an obvious enhancement of power conversion efficiency from 18.70% to 20.05% for perovskite solar cells, which originates from the surface passivation of the perovskite film with reduced trap state densities and suppressed interfacial charge recombination.

Ionic defects at the surfaces of organolead halide perovskite films are detrimental to both the efficiency and stability of perovskite solar cells (PSCs). Herein, sodium p‐toluenesulfonate (STS) is applied during the surface modification of perovskite layer for the first time, leading to the efficient surface passivation of the perovskite film and consequently significant enhancements in both efficiency and stability of mixed‐cation PSC devices. Upon incorporating STS atop the perovskite layer, the power conversion efficiency of the Cs_0.05MA_0.12FA_0.83PbI_2.55Br_0.45 (abbreviated as CsMAFA) mesoporous‐structure mixed‐cation PSC devices improves from 18.70% to 20.05% with reduced hysteresis. The sulfonate (–SO₃ ⁻) anion of STS coordinates with the Pb²⁺ of CsMAFA perovskite, and the Na⁺ cation of STS electrostatically interacts with the anions (I⁻/Br⁻) of CsMAFA perovskite, resulting in the surface passivation of the CsMAFA perovskite film with reduced electron and hole trap state densities. In addition, STS modification induces an upshift of the valence band of perovskite, facilitating hole extraction from the perovskite layer to the hole transport layer with suppressed interfacial charge recombination. Moreover, such a trap state passivation of perovskite film leads to improvement of the ambient stability of PSC devices.

The inverse temperature‐dependencies of the photovoltaic parameters in MAPbI₃ perovskite solar cells lead to obtaining a peak efficiency of 21.4% at 220 K. These T ‐varied behaviors are related to combined properties of improved interfacial charge extraction, reduced charge trap density, and suppressed nonradiative recombination at lower temperatures.

Abstract

Understanding the factors that limit the performance of perovskite solar cells (PSCs) can be enriched by detailed temperature (T )‐dependent studies. Based on p‐i‐n type PSCs with prototype methylammonium lead triiodide (MAPbI₃) perovskite absorbers, T ‐dependent photovoltaic properties are explored and negative T ‐coefficients for the three device parameters (V _OC, J _SC, and FF) are observed within a wide low T ‐range, leading to a maximum power conversion efficiency (PCE) of 21.4% with an impressive fill factor (FF) approaching 82% at 220 K. These T ‐behaviors are explained by the enhanced interfacial charge transfer, reduced charge trapping with suppressed nonradiative recombination and narrowed optical bandgap at lower T . By comparing the T ‐dependent device behaviors based on MAPbI₃ devices containing a PASP passivation layer, enhanced PCE at room temperature is observed but different tendencies showing attenuating T ‐dependencies of J _SC and FF, which eventually leads to nearly T ‐invariable PCEs. These results indicate that charge extraction with the utilized all‐organic charge transporting layers is not a limiting factor for low‐T device operation, meanwhile the trap passivation layer of choice can play a role in the T ‐dependent photovoltaic properties and thus needs to be considered for PSCs operating in a temperature‐variable environment.

SnO₂ and perovskite have been bridged with multifunctional graphdiyne. Such delicate interface modification boosted the performance of solar cells in energy band alignment, electron mobility improvement, controllable perovskite growth inducement, and interface defect passivation.

Abstract

The matching of charge transport layer and photoactive layer is critical in solar energy conversion devices, especially for planar perovskite solar cells based on the SnO₂ electron‐transfer layer (ETL) owing to its unmatched photogenerated electron and hole extraction rates. Graphdiyne (GDY) with multi‐roles has been incorporated to maximize the matching between SnO₂ and perovskite regarding electron extraction rate optimization and interface engineering towards both perovskite crystallization process and subsequent photovoltaic service duration. The GDY doped SnO₂ layer has fourfold improved electron mobility due to freshly formed C−O σ bond and more facilitated band alignment. The enhanced hydrophobicity inhibits heterogeneous perovskite nucleation, contributing to a high‐quality film with diminished grain boundaries and lower defect density. Also, the interfacial passivation of Pb−I anti‐site defects has been demonstrated via GDY introduction.

Hysteresis in perovskite solar cells is suppressed with the insertion of a phenyl‐C61‐butyric acid methyl ester (PCBM) layer. In situ PL imaging is employed to observe the ionic migration in the perovskite layer, perovskite/PCBM bilayer and PPCBM bilayer. The mobilizable PCBM molecules are able to diffuse into the perovskite and therein passivate iodine ions/vacancies, thus reducing the hysteresis.

Abstract

The power conversion efficiency of inorganic–organic hybrid lead halide perovskite solar cells (PSCs) is approaching that of those made from single crystalline silicon; however, they still experience problems such as hysteresis and photo/electrical‐field‐induced degradation. Evidences consistently show that ionic migration is critical for these detrimental behaviors, but direct in‐situ studies are still lacking to elucidate the respective kinetics. Three different PSCs incorporating phenyl‐C61‐butyric acid methyl ester (PCBM) and a polymerized form (PPCBM) is fabricated to clarify the function of fullerenes towards ionic migration in perovskites: 1) single perovskite layer, 2) perovskite/PCBM bilayer, 3) perovskite/PPCBM bilayer, where the fullerene molecules are covalently linked to a polymer backbone impeding fullerene inter‐diffusion. By employing wide‐field photoluminescence imaging microscopy, the migration of iodine ions/vacancies under an external electrical field is studied. The polymerized PPCBM layer barely suppresses ionic migration, whereas PCBM readily does. Temperature‐dependent chronoamperometric measurements demonstrate the reduction of activation energy with the aid of PCBM and X‐ray photoemission spectroscopy (XPS) measurements show that PCBM molecules are viable to diffuse into the perovskite layer and passivate iodine related defects. This passivation significantly reduces iodine ions/vacancies, leading to a reduction of built‐in field modulation and interfacial barriers.

State‐of‐the‐art perovskite solar cells generally consist of an excess of lead iodide (PbI₂) as passivator. In this work, ligand‐modulation technology is demonstrated to fabricate vertically distributed PbI₂ nanosheets between the perovskite grain boundaries, which enhances the passivation effect of PbI₂ and improves the power conversion efficiency and stability of perovskite solar cells.

Abstract

Excess lead iodide (PbI₂), as a defect passivation material in perovskite films, contributes to the longer carrier lifetime and reduced halide vacancies for high‐efficiency perovskite solar cells. However, the random distribution of excess PbI₂ also leads to accelerated degradation of the perovskite layer. Inspired by nanocrystal synthesis, here, a universal ligand‐modulation technology is developed to modulate the shape and distribution of excess PbI₂ in perovskite films. By adding certain ligands, perovskite films with vertically distributed PbI₂ nanosheets between the grain boundaries are successfully achieved, which reduces the nonradiative recombination and trap density of the perovskite layer. Thus, the power conversion efficiency of the modulated device increases from 20% to 22% compared to the control device. In addition, benefiting from the vertical distribution of excess PbI₂ and the hydrophobic nature of the surface ligands, the modulated devices exhibit much longer stability, retaining 72% of their initial efficiency after 360 h constant illumination under maximum power point tracking measurement.

A highly stable phosphonate‐functionalized viologen, BPP−Vi, with 1.23 m solubility and −0.462 V versus SHE reduction potential at pH = 9, composes the negolyte for an aqueous organic‐based flow battery operating at nearly neutral pH against a ferro/ferricyanide posolyte. The flow battery exhibits an open circuit voltage of 0.9 V and a capacity fade rate of 0.016% per day or 0.00069% per cycle.

Abstract

A highly stable phosphonate‐functionalized viologen is introduced as the redox‐active material in a negative potential electrolyte for aqueous redox flow batteries (ARFBs) operating at nearly neutral pH. The solubility is 1.23 m and the reduction potential is the lowest of any substituted viologen utilized in a flow battery, reaching −0.462 V versus SHE at pH = 9. The negative charges in both the oxidized and the reduced states of 1,1′‐bis(3‐phosphonopropyl)‐[4,4′‐bipyridine]‐1,1′‐diium dibromide (BPP−Vi ) effect low permeability in cation exchange membranes and suppress a bimolecular mechanism of viologen decomposition. A flow battery pairing BPP−Vi with a ferrocyanide‐based positive potential electrolyte across an inexpensive, non‐fluorinated cation exchange membrane at pH = 9 exhibits an open‐circuit voltage of 0.9 V and a capacity fade rate of 0.016% per day or 0.00069% per cycle. Overcharging leads to viologen decomposition, causing irreversible capacity fade. This work introduces extremely stable, extremely low‐permeating and low reduction potential redox active materials into near neutral ARFBs.