Chen Weijie

High‐performance all‐inorganic perovskite solar cells with efficiency exceeding 15% are achieved via short‐period deep‐ultraviolet (DUV) photoactivation process. The DUV treatment can efficiently decrease the work function, resulting in better band alignment. The unencapsulated device exhibits enhanced operational stability under continuous simulated sunlight illumination, thermal stability, and outstanding air stability after 30 days of storage under N₂ condition.

All‐inorganic perovskite CsPbI₂Br have been regarded as a promising candidate to tackle the thermal instability issue of organic–inorganic perovskite solar cells. However, the serious interfacial charge recombination and large voltage potential loss in cells circumscribe their performance and commercialization. Herein, a facile approach is demonstrated in which the SnO₂ electron transport layer is modified with short‐period deep‐ultraviolet (DUV) photoactivation process to decrease the work function and achieve better energy alignment with the conduction band of perovskites. Such modification triggers efficient charge transfer and reduces the charge recombination. Moreover, first‐principles calculation further demonstrates that DUV‐treated SnO₂ can strengthen the interface interaction, reduce the interface stress caused by lattice mismatch, induce more ordered perovskite structure, enlarge transfer charge from 0.71 to 2.33 e, gain larger built‐in field (from 0.74 to 2.09 eV), lower work function, and smaller conduction band offset. Thus, all‐inorganic CsPbI₂Br solar cells based on DUV‐treated SnO₂ exhibit a significant enhancement in power conversion efficiency, and the champion cell achieves an elevated efficiency of 15.1% with a superior V _oc of 1.22 V and better stability.

A fused‐ring electron acceptor (F10IC2) with solubilizing alkoxy side chains is designed and synthesized, and as‐cast blade‐coated organic solar cells based on PTB7‐Th: F10IC2 blended films are fabricated from chlorobenzene or chlorine‐free o‐xylene as solvents in air without any post‐treatment deliver a PCE of 12.5% and 11.4%, respectively.

The rapid development of organic solar cells (OSCs) based on nonfullerene acceptors has achieved significant breakthroughs in the power conversion efficiency (PCE) of spin‐coated devices. However, the spin‐coating method in a protective atmosphere seems unsuitable for the practical printing of high‐performance solar panels. In addition, the use of highly toxic solvents is also a stumbling block to the commercial application of OSCs. Thus, photoactive materials for scalable coating and ecofriendly manufacturing approaches are necessary to be developed for OSCs. Herein, a fused‐ring electron acceptor named F10IC2 bearing a decacycle core and solubilizing alkoxyl side chains is synthesized and applied in as‐cast blade‐coated OSCs by blending with polymer donor PTB7‐Th. As‐cast OSCs based on PTB7‐Th: F10IC2 blended films fabricated from chlorobenzene or chlorine‐free o‐xylene solvents in air without any posttreatment deliver a PCE of 12.5% and 11.4%, respectively, which are among the highest values reported for as‐cast blade‐coated OSCs. Herein, a strategy of alkoxyl solubilizing to design high‐performance material systems for ecofriendly scalable OSCs is provided, which is suitable for future industrial production.

Low‐temperature‐processed Zr/F co‐doped SnO₂ is an excellent successor of electron transport layers (ETLs) for high‐efficiency planar perovskite solar cells. Benefiting from an accurate energy level match and enhanced ETL conductivity, the photoelectric conversion efficiency, and hysteresis effect are obviously improved.

The energy band position and conductivity of electron transport layers (ETLs) are essential factors that restrict the efficiency of planar perovskite solar cells (p‐PSCs). Tin oxide (SnO₂) has become a primary material in ETLs due to its mild synthesis condition, but its low conduction band position and limited intrinsic carriers are disadvantageous in electron transport. To solve these problems, this work exquisitely designs a Zr/F co‐doped SnO₂ ETL. The doping of Zr can raise the conduction band of SnO₂, which reduces the energy barrier in electron extraction and inhibits the interface recombination between the ETL and perovskite. The open‐circuit voltage (V _OC) of p‐PSCs consequently increases. F⁻ doping belongs to n‐type doping. Thus, it equips SnO₂ with a large number of free electrons and improves the conductivity of the ETL and short‐circuit current (J _SC). The device based on Zr/F co‐doped ETL achieves a high efficiency of 19.19% and exhibits a reduced hysteresis effect, which is more satisfactory than that of a pristine device (17.35%). Overall, this research successfully adjusts the energy band match and boosts the conductivity of ETL via Zr/F co‐doping. The results provide an effective strategy for fabricating high‐efficiency p‐PSCs.

The nonionic polymer with multiple amino groups is introduced to passivate both metal‐ and halide‐induced defects of all‐inorganic CsPbI₂Br perovskite by coordination and hydrogen bonds, simultaneously. Consequently, a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film are achieved, which boosts the efficiency of perovskite solar cells up to 15.48% with excellent humidity stability.

The all‐inorganic CsPbI₂Br perovskite with superior thermal durability faces challenges of low‐phase stability and high moisture sensitivity. Herein, a nonionic additive of polyethyleneimine (PEI) with multiple amino groups is introduced to form hydrogen bond with I⁻/Br⁻ ions and coordinate with Pb²⁺/Cs⁺ ions simultaneously. The strong interplay between PEI and CsPbI₂Br achieves a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film, which boosts the power conversion efficiency (PCE) of perovskite solar cells to 15.48%. The hydrophobic long alkyl chain of PEI greatly improves the humidity resistance, retaining 81.9% of initial PCE of zjr unsealed device under 20 ± 5% relative humidity (RH) for 500 h. Remarkably, a PCE of 13.37% is achieved by the device based on CsPbI₂Br–PEI film processed under ambient condition (≈22% RH, ≈25 °C).

Post‐treating the mesoporous TiO₂/ZrO₂/carbon triple layer by alkali metal sulfonate compounds enables a significantly enhanced photovoltage for hole‐conductor‐free printable mesoscopic perovskite solar cells. The devices demonstrate high operational stability, retaining 91.7% of their initial efficiency after 1000 h continuous operation at the maximum power point under 1 sun illumination.

Triple‐mesoscopic perovskite solar cells (PSCs) based on TiO₂/ZrO₂/carbon architecture have attracted much attention due to their excellent long‐term stability and screen‐printing technique‐based fabrication process. However, the relatively low open‐circuit voltage (V _OC) limits the further improvement of power conversion efficiency (PCE) for triple‐mesoscopic PSCs. Herein, 2‐phenyl‐5‐benzimidazole sulfonate‐Na to post‐treat the triple‐mesoscopic structured scaffold is introduced. The conduction band of the mesoporous TiO₂ layer (electron transport layer [ETL]) is significantly shifted up from −4.22 to −4.11 eV, which favors the electron transfer from the perovskite absorber to the ETL. At the same time, the recombination at the interface of ETL/perovskite is effectively suppressed. Correspondingly, the V _OC and fill factor (FF) of the devices are enhanced without sacrificing the photocurrent density (J _SC). With optimal post‐treatment conditions, the champion device delivers a V _OC of 1.02 V and an FF of 0.70 with J _SC of 23.06 mA cm⁻², showing an overall PCE of 16.51%. After 1000 h continuous operation at the maximum power point under AM1.5G 1 sun illumination, the devices can maintain 91.7% of the initial efficiency. This simple procedure and significant photovoltage enhancement render this method promising for fabricating efficient PSCs based on mesoporous charge transport layers.

Herein, large‐area silicon heterojunction solar cells with efficiency of 22.0% using commercial‐grade p‐type Czochralski silicon wafers are demonstrated. An advanced hydrogenation process is developed to overcome the impact of boron–oxygen light‐induced degradation in these p‐type cells, resulting in stable V _OC of 736 mV. This can be a potential pathway to lower cost high‐efficiency solar cells.

Herein, large‐area defect‐engineered p‐type silicon heterojunction (SHJ) solar cells using standard 1.6 Ω cm commercial‐grade boron‐doped Czochralski (Cz) silicon wafers are fabricated. It is demonstrated that despite achieving an open‐circuit voltage of 735 mV with an efficiency of 21.6% for gettered samples, without appropriate treatment, the cells are heavily susceptible to boron–oxygen‐related light‐induced degradation (LID), with the effective lifetime at maximum power point decreasing to 13 μs. This degradation results in a loss of efficiency of more than 3.1%_abs (14.3%_rel) after 48 h of light soaking. However, the addition of an advanced hydrogenation postcell fabrication process increases the efficiency by 0.2%_abs to 21.8%, and dramatically reduces susceptibility of LID, decreasing the extent of degradation to 0.2%_abs (0.9%_rel). A peak stable independently measured efficiency of 22.0% with an open‐circuit voltage (V _OC) of 736 mV is achieved with the addition of a dedicated high‐temperature prefabrication hydrogenation. These results indicate that p‐type Cz wafers can be used to fabricate stable, next‐generation high‐efficiency solar cells using silicon heterojunctions or other passivated contact architectures requiring V _OCS well above 700 mV.

The surface and bulk defects of perovskite films are simultaneously passivated through the treatment of CsBr/methanol solution, in which the methanol helps CsBr penetrate the depth of the perovskite and reconstruct high‐quality films. This strategy can effectively improve the photovoltaic performance and operational stability of the resultant devices.

It is challenging to passivate defects that are buried in the depth of perovskite films; most of the reported passivation methods cannot reach the deep defects. Herein, methanol is adopted as a dual‐functional reagent to not only act as a solvent but also help the dissolved ions penetrate the depth of perovskite films. By treating the as‐prepared perovskite films with CsBr/methanol solution, Br⁻ ions can react with the undercoordinated Pb²⁺, and Cs⁺ ions can fill in the cation vacancies. This strategy enables surface and bulk defects passivation to be achieved simultaneously. The nonradiative recombination of the double‐passivated devices is significantly suppressed and the migration of charged defects is remarkably hindered. As a result, an improved power conversion efficiency of 19.5% and an open‐circuit voltage of 1.183 V is achieved. Moreover, the passivated device can retain ≈80% of the initial efficiency after working for 500 h at maximum power point under 1‐sun illumination, whereas the pristine device reaches 80% of the initial efficiency after only 90 h. This work demonstrates that surface and bulk defects passivation is critical to improve the efficiency and long‐term operational stability of the perovskite solar cells.

Three novel donor–π‐bridge–acceptor (D–π–A)‐type small organic molecules are designed and synthesized as dopant‐free hole transport materials for perovskite solar cells. Combination of triazatruxene donor, terthiophene π‐bridge, and dicyanovinylene N‐ethyl rhodanine electron‐accepting unit as CI‐B3 creates well‐ordered edge‐on aggregated π–π stacking. Solar cell performance and long‐term stability are significantly improved.

Three donor–π‐bridge–acceptor (D–π–A)‐type organic small molecules coded CI‐B1, CI‐B2, and CI‐B3 are designed, synthesized, and used as dopant‐free hole transporting materials (HTMs) for perovskite solar cells (PSCs). The strong electron‐donating triazatruxene central core (D), terthiophene conjugated arms (π), and three different strong electron‐accepting units (A) provide high intramolecular charge transfer nature and eliminate the need of dopants during the fabrication of PSCs. HTMs are investigated to understand the effect of terminal functional groups on the PSC performance. Interestingly, due to the change of end‐capping, three different organizations of self‐assembly with π–π stacking are observed in the solid thin films. Dopant‐free CI‐B1, CI‐B2, CI‐B3, and spiro‐OMeTAD with dopants are used with triple cation perovskite composition Cs_0.1(MA_0.15FA_0.85)_0.9Pb(I_0.85Br_0.15)₃ (MA: CH₃NH₃ ⁺, FA: NHCHNH₃ ⁺) in n‐i‐p architecture. The cells prepared with CI‐B3 not only exhibits a comparable power conversion efficiency (PCE) of 17.54% to the state‐of‐art of spiro‐OMeTAD with dopants (18.02%), but also demonstrates improved long‐term stability, maintaining 88% of its original PCE after 1000 h of illumination. The superior photovoltaic performance, synthetic simplicity, dopant‐free nature, high durability, and edge‐on molecular orientation of CI‐B3 show its great promise as a HTM candidate for efficient and stable PSCs.

The role of energy offset between the optical bandgap and charge transfer (CT) state energies in nonradiative voltage loss ΔV _nr in organic solar cells is discussed. It is found that the ΔV _nr reduces considerably down to 0.185 V, when local excited and CT states are remarkably close in energy.

The voltage loss incurred by nonradiative charge recombination should be reduced to further improve the power conversion efficiency of organic solar cells (OSCs). This work discusses the nonradiative voltage loss in OSCs with systematically controlled energy offset between optical bandgap and charge transfer (CT) states. It is demonstrated that the nonradiative voltage loss is a function of the energy offset; it drops sharply with decreasing energy offset. By measuring the quantum yields of electroluminescence from OSCs and decay kinetics of CT states, it is found that the radiative decay rate of CT states becomes larger when the energy offset is negligible compared with those in conventional OSCs with sufficient energy offset. This behavior is rationalized by hybridization between CT and local excited states, resulting in a considerable enhancement of the oscillator strength of CT states. Based on a trend observed in this study, the precise mechanism by which the energy offset affects the nonradiative voltage loss is discussed.

Sb₂O₃/Ag/Sb₂O₃ multilayer electrodes are used in organic solar cells (OSCs) to demonstrate colorful semitransparent devices. Notably, the effect of thickness of each layer in the electrode on the optical properties and performance of organic solar cells is thoroughly investigated. By matching the electrodes with the absorption characteristics of the active layers, esthetically colored, semitransparent OSCs can be fabricated.

The pace of advancement and increasing power conversion efficiencies (PCEs) have provided the possibility for organic solar cells (OSCs) to be commercialized in a variety of applications, including semitransparent photovoltaics. The application of dielectric–metal–dielectric (DMD) transparent electrodes to OSCs is an effective way to achieve semitransparent OSCs with different colors. Herein, a DMD multilayer structure based on two Sb₂O₃ layers and silver (Ag) thin films as the top electrode is introduced. An ultrathin Sb₂O₃ layer is deposited between the electron transport layer and the Ag film as a bottom layer for the Sb₂O₃/Ag/Sb₂O₃ electrode; this layer inhibits Ag atom diffusion and aggregation, which leads to uniform formation of ultrathin Ag films. The thickness of the middle metal layer influences fill factor and short‐circuit current density values, which correlate well with device resistance and light reflection. For the top Sb₂O₃ layer, the thickness allows the selective transmittance of specific wavelengths of visible light while reflecting wavelengths that are not transmitted, creating a dichroic effect. OSCs are successfully fabricated using three kinds of colorful active layers in conjunction with Sb₂O₃/Ag/Sb₂O₃ electrodes, resulting in vividly colored devices with PCE of 6.33–7.88% and average visible transmittances of 23–30%.

An efficient and stable tin perovskite solar cell with a graded heterostructure which is composed of narrow‐bandgap and wide‐bandgap tin perovskites is reported. Such heterostructure facilitates charge extraction and suppresses the oxidation process of Sn²⁺ to Sn⁴⁺. Consequently, the device achieves a maximum power conversion efficiency of 11% with better operational stability.

Lead‐free tin perovskite solar cells (TPSCs) have attracted widespread attention in recent years due to their low toxicity, suitable bandgap, and high carrier mobility. However, the photovoltage and efficiency of TPSCs are still much lower than those of the lead counterparts because of the high trap density and unfavorable band structure in tin perovskite films. To overcome these issues, efficient and stable TPSCs with a graded heterostructure of light‐absorbing layer are reported, in which the narrow‐bandgap tin perovskite dominates at the bulk, whereas the wide‐bandgap tin perovskite is distributed with a gradient from bulk to surface. This heterostructure can selectively extract the photogenerated charge carriers at the perovskite/electron transport layer interface, reduce the density of trap states, and impede the oxidation process of Sn²⁺ to Sn⁴⁺ in air. As a consequence, this graded heterostructure of tin perovskite layer contributes to an increase of 120 mV in the open‐circuit voltage and a maximum power conversion efficiency of 11% for TPSCs with longer operational stability.

A simple and effective method of fine‐tuning the energy level of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) is demonstrated. The as‐prepared hole‐transporting material aligns well with the highest occupied molecular orbital level of the electron donor in nonfullerene‐based organic photovoltaic (OPV) devices in inverted architecture, reaching a power conversion efficiency of 10%, which would benefit the future commercialization of highly efficient OPV devices.

Solution‐processable hole‐transporting materials are demonstrated to improve the performance of nonfullerene‐based organic photovoltaic devices in an inverted structure. A vanadium oxide (VO _X ) precursor, used as a sol–gel, is mixed with commercial poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to form a well‐dispersed VO _X :PEDOT:PSS solution. The work function and molecular distribution of the VO _X :PEDOT:PSS thin film are examined by ultraviolet photoelectron spectroscopy (UPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), respectively. Unlike conventional PEDOT:PSS, VO _X :PEDOT:PSS not only is compatible with highly hydrophobic photoactive layers but also aligns well with the highest occupied molecular orbital (HOMO) level of the polymer donor, reaching a power conversion efficiency of 10% (≈100% boost) and achieving an excellent device stability.

A dual‐functionalized bidentate molecule 2‐(2′‐thienyl)pyridine (2‐ThPy) is introduced to modulate perovskite crystallization and passivate halogen vacancy defects. Compared with monodentate counterparts, 2‐ThPy can anchor Pb²⁺ sites via S and N atomic bonding simultaneously. Consequently, 2‐ThPy‐treated CsPbI₂Br perovskite solar cells achieve a champion power conversion efficiency of 12.69% with negligible hysteresis and exhibit prominent moisture stability.

All inorganic mixed‐halide CsPbI₂Br perovskites with suitable bandgap and superior thermal durability have ignited rising interests in the field of perovskite solar cells (PSCs). However, the serious energy losses derived from deleterious trap‐assisted defects–induced notorious nonradiative recombination and inferior moisture durability are still the primary hindrance on the way to develop high‐performance CsPbI₂Br PSCs. Herein, a novel passivation strategy is presented by introducing dual‐functionalized bidentate molecule 2‐(2′‐thienyl)pyridine (2‐ThPy) to modulate perovskite crystallization and passivate halogen vacancy defects. Compared with monodentate counterparts, 2‐ThPy can anchor Pb²⁺ sites via S and N atomic bonding simultaneously, and the synthesized CsPbI₂Br films exhibit enlarged grain size, show advantages to passivate defect states, and dramatically reduce trap density, thereby lessening the detrimental carrier recombination. Consequently, a champion power conversion efficiency (PCE) of 12.69% with negligible hysteresis is delivered for the fabricated CsPbI₂Br PSCs treated with 2‐ThPy. Moreover, the moisture stability of CsPbI₂Br PSCs with 2‐ThPy is also greatly enhanced, and the device without encapsulation retains 92% of initial PCE value after 30 days aging under 25 °C and 40% relative humidity in ambient environment. The bidentate molecules passivation strategy paves a promising avenue to implement efficient and stable inorganic PSCs.

The article studies SnO₂'s role in the stability of air‐processed planar perovskite solar cells. UV treatment of sub‐cells (500 h N₂ environment) speeds up the depletion of perovskite films, leading to excess PbI₂ formation at the perovskite surfaces. This inadvertently leads to full device stabilization through passivation as seen in maximum power point (MPP) measurements of perovskite solar cells incorporating UV‐treated sub‐cells.

SnO₂ is nowadays the widely preferred material as an electron transport layer (ETL) in most n‐i‐p planar perovskite solar cells (PSCs) due to its facility for ambient, low temperature processing, and ultraviolet (UV) stability. Most reports published so far study device stability on full cells. Herein, the role of slot‐die‐coated SnO₂ on air‐processed planar PSCs by analyzing sub‐cells (indium tin oxide [ITO]/SnO₂/perovskite) under UV exposure is investigated. Results from UV–vis spectroscopy, depth profiling using X‐ray diffraction measurement in grazing incidence mode (GIXRD), X‐ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy measurements show that UV treatment of ITO/SnO₂/perovskite leads to a reduced electron transfer to the SnO₂ layer and a gradual increase in the amount of PbI₂ toward the perovskite surfaces. Subsequently, hole transport layer (HTL) and electrodes are applied on SnO₂/perovskite interfaces (UV‐treated and non‐UV‐treated) and complete devices are fabricated. Device performance is compared and analyzed through J –V curves and maximum power point (MPP) tracking. Results show that devices built on a UV‐treated SnO₂/perovskite interface show better stability attributed to the presence of excess PbI₂ resulting in a passivation effect. Challenges in uniform film formation of slot‐die‐coated SnO₂ and potential solutions using a polymeric additive are also highlighted.

Herein, perovskite composite nanofibers are incorporated into a solar yarn through an electrospinning process, to work as the photoactive layer of the device. Electrospinning is conducted at high relative humidity (75%) and voltage (17 kV) to enhance perovskite crystal growth on polyvinylpyrrolidone (PVP) nanofibers. The resulting yarn demonstrates a 15.7% efficiency, with a good absorption peak, flexibility, and increased active lifetime.

A flexible perovskite solar yarn with an impressive active lifetime (>216 h) and an exceptional photon conversion efficiency is prepared under ordinary conditions. The champion device demonstrates an average linear mass density of 0.89 mg cm⁻¹ and can be bent over a loop diameter of 2.5 mm, with a negligible efficiency loss. Photoactive nanofibers composed of a polyvinylpyrrolidone (PVP) central strain and a perovskite phase on the surface (with average grain size of 275 ± 14.3 nm), are prepared by electrospinning, at 18 kV, relative humidity of 75%, and a temperature of 25 °C. This bilayered configuration promises superior mechanical strength and flexibility, together with an excellent photovoltaic character, compared with their dip coated counterparts. Photoactive perovskite nanofibers are incorporated into a plied‐solar yarn, with an organic hole‐conductive layer, poly(3‐hexylthiophene‐2,5‐diyl)‐coated on silver yarn electrode, and a composite electron conductive layer, phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM)‐SnO₂ coated on a carbon yarn. An individual double‐twisted solar yarns yields 15.7% champion power conversion efficiency, while a 30.5 mm × 30.5 mm active area of plain‐woven fabric generates a maximum power density of 1.26 mW cm⁻² under one sun (1000 W m⁻²) solar illumination.

Herein, the halogenation effect on morphology and miscibility in high‐performance small molecular acceptors is characterized and analyzed in several material combinations. Good efficiencies are achieved in asymmetric systems and Y series systems. The relationship between device performances and miscibility in specific ranges is in agreement with previous studies.

A multitude of studies have been conducted on organic solar cells (OSCs) to understand how end group halogenation changes the property of the small molecular acceptors (SMAs) energetically, morphologically, and so on. But how the halogenation impacts the miscibility between SMAs and polymers, which is an important index to thermodynamically predict and understand the morphology of blend films, has not been systematically studied, particularly for the state‐of‐the‐art polymer–SMA blends. Herein, three series of asymmetric or symmetric SMAs, all reported recently with high photovoltaic performances, are used to investigate the effect of halogenation on miscibility, crystallinity, and solar cell performance. Using the asymmetric SMA named TPIC, and its derivatives (TPIC‐4F and TPIC‐4Cl) as the focus, it is revealed that the enhancement in solar cell performance for the halogenated SMAs is to reduce the miscibility between the acceptor and donor, which leads to a more favorable morphology, enhanced charge transport, and an extended absorption range. Similarly, the halogenation‐induced reduction in miscibility for the initially overmixed donor:acceptor blend is also demonstrated in the symmetric ITIC and the state‐of‐the‐art BTP series, where attractive power conversion efficiencies (PCEs) of 16.5% and 16.8%, respectively, are achieved by the halogenated‐SMA‐based devices in each series.

A composite consisting of 1D cation‐doped TiO₂ brookite nanorod embedded by 0D fullerene is investigated as a top modification buffer for inverted perovskite photovoltaic (IP‐PV) cells. The resultant IP‐PV displays an efficiency exceeding 22% with a favorable stability. This work opens up more opportunities in expanding the material inventory for charge transfer layer in perovskite solar cells development and application.

Abstract

Simultaneously achieving high efficiency and high durability in perovskite solar cells is a critical step toward the commercialization of this technology. Inverted perovskite photovoltaic (IP‐PV) cells incorporating robust and low levelized‐cost‐of‐energy (LCOE) buffer layers are supposed to be a promising solution to this target. However, insufficient inventory of materials for back‐electrode buffers substantially limits the development of IP‐PV. Herein, a composite consisting of 1D cation‐doped TiO₂ brookite nanorod (NR) embedded by 0D fullerene is investigated as a top modification buffer for IP‐PV. The cathode buffer is constructed by introducing fullerene to fill the interstitial space of the TiO₂ NR matrix. Meanwhile, cations of transition metal Co or Fe are doped into the TiO₂ NR to further tune the electronic property. Such a top buffer exhibits multifold advantages, including improved film uniformity, enhanced electron extraction and transfer ability, better energy level matching with perovskite, and stronger moisture resistance. Correspondingly, the resultant IP‐PV displays an efficiency exceeding 22% with a 22‐fold prolonged working lifetime. The strategy not only provides an essential addition to the material inventory for top electron buffers by introducing the 0D:1D composite concept, but also opens a new avenue to optimize perovskite PVs with desirable properties.

Silver atoms incorporated into the inorganic halide perovskite Cs₃Bi₂Br₉ to form Cs₂AgBiBr₆ eliminates the strong localization of electron–hole pairs and makes the electronic bands distribution more dispersible and further changes the photoelectric properties including band structure, exciton binding energy, charge carrier mobility, and carrier relaxation lifetime, which lead to a remarkable enhancement in photocatalytic hydrogen evolution under visible light.

Abstract

Lead‐free inorganic halide perovskites have triggered appealing interests in various energy‐related applications including solar cells and photocatalysis. However, why perovskite‐structured materials exhibit excellent photoelectric properties and how the unique crystalline structures affect the charge behaviors are still not well elucidated but essentially desired. Herein, taking inorganic halide perovskite Cs₃Bi₂Br₉ as a prototype, the significant derivation process of silver atoms incorporation to induce the structural transformation from Cs₃Bi₂Br₉ to Cs₂AgBiBr₆, which brings about dramatic differences in photoelectric properties is unraveled. It is demonstrated that the silver incorporation results in the co‐operated orbitals hybridization, which makes the electronic distributions in conduction and valence bands of Cs₂AgBiBr₆ more dispersible, eliminating the strong localization of electron–hole pairs. As consequences of the electronic structures derivation, exhilarating changes in photoelectric properties like band structure, exciton binding energy, and charge carrier dynamics are verified experimentally and theoretically. Using photocatalytic hydrogen evolution activity under visible light as a typical evaluation, such crystalline structure transformation contributes to a more than 100‐fold enhancement in photocatalytic performances compared with pristine Cs₃Bi₂Br₉, verifying the significant effect of structural derivations on the exhibited performances. The findings will provide evidences for understanding the origin of photoelectric properties for perovskites semiconductors in solar energy conversion.

A composite consisting of 1D cation‐doped TiO₂ brookite nanorod embedded by 0D fullerene is investigated as a top modification buffer for inverted perovskite photovoltaic (IP‐PV) cells. The resultant IP‐PV displays an efficiency exceeding 22% with a favorable stability. This work opens up more opportunities in expanding the material inventory for charge transfer layer in perovskite solar cells development and application.

Abstract

Simultaneously achieving high efficiency and high durability in perovskite solar cells is a critical step toward the commercialization of this technology. Inverted perovskite photovoltaic (IP‐PV) cells incorporating robust and low levelized‐cost‐of‐energy (LCOE) buffer layers are supposed to be a promising solution to this target. However, insufficient inventory of materials for back‐electrode buffers substantially limits the development of IP‐PV. Herein, a composite consisting of 1D cation‐doped TiO₂ brookite nanorod (NR) embedded by 0D fullerene is investigated as a top modification buffer for IP‐PV. The cathode buffer is constructed by introducing fullerene to fill the interstitial space of the TiO₂ NR matrix. Meanwhile, cations of transition metal Co or Fe are doped into the TiO₂ NR to further tune the electronic property. Such a top buffer exhibits multifold advantages, including improved film uniformity, enhanced electron extraction and transfer ability, better energy level matching with perovskite, and stronger moisture resistance. Correspondingly, the resultant IP‐PV displays an efficiency exceeding 22% with a 22‐fold prolonged working lifetime. The strategy not only provides an essential addition to the material inventory for top electron buffers by introducing the 0D:1D composite concept, but also opens a new avenue to optimize perovskite PVs with desirable properties.

Publication date: 15 July 2020

Source: Joule, Volume 4, Issue 7

Author(s): Qin Hu, Wei Chen, Wenqiang Yang, Yu Li, Yecheng Zhou, Bryon W. Larson, Justin C. Johnson, Yi-Hsien Lu, Wenkai Zhong, Jinqiu Xu, Liana Klivansky, Cheng Wang, Miquel Salmeron, Aleksandra B. Djurišić, Feng Liu, Zhubing He, Rui Zhu, Thomas P. Russell

Publication date: 15 July 2020

Source: Joule, Volume 4, Issue 7

Author(s): Xu Chen, Ziyan Jia, Zeng Chen, Tingming Jiang, Lizhong Bai, Feng Tao, Jianwu Chen, Xinya Chen, Tianyu Liu, Xuehui Xu, Chenying Yang, Weidong Shen, Wei E.I. Sha, Haiming Zhu, Yang (Michael) Yang

An aryl diammonium iodide: PDMAI is demonstrated first to be highly promising to enhance open‐circuit voltage, short‐circuit current, and stability of FAMAPbI₃ based perovskite solar cells through surface passivation. Theoretical calculation suggests a stronger energy binding between PDMAI and perovskite surface. This work provides a new passivation strategy for efficient and stable perovskite solar cells.

Abstract

Surface passivation is increasingly one of the most prominent strategies to promote the efficiency and stability of perovskite solar cells (PSCs). However, most passivation molecules hinder carrier extraction due to poorly conductive aggregation between perovskite surface and carrier transportation layer. Herein, a novel molecule: p‐phenyl dimethylammonium iodide (PDMAI) with ammonium group on both terminals is introduced, and its passivation effect is systematically investigated. It is found that PDMAI can mitigate defects at the surface and promote carrier extraction from perovskite to the hole transporting layer, leading to a lift of open‐circuit voltage of 40 mV. Profiting from superior PDMAI passivation, the average efficiency of PSCs has been elevated from 19.69% to 20.99%. As demonstrated with density functional theory calculations, PDMAI probably tends to anchor onto the perovskite surface with both NH₃I tails, and enhances the adhesion and contact to perovskite layer. The exposed hydrophobic aryl core protects perovskite against detrimental environmental factors. In addition, the alkyl component between aryl and ammonium groups is demonstrated to be essentially vital in triggering passivation function, which offers the guidance for the design of passivation molecules.

When introduced beneath the 3D perovskite layer, the 2D perovskite seeding layer acts as a template for growth in the planar direction, resulting in an increase in perovskite grains with less and narrow grain boundaries. As a result, the hydrophobicity of the film increases resulting in better stability and improved efficiency when the films are processed in air.

Abstract

Despite the record power conversion efficiencies, inverted perovskite solar cells (PSCs) are still looking to overcome the challenge of moisture instability. This is mitigated by introducing 2D perovskite at the base of a 3D perovskite via coating of ethylenediamine bications on top of the hole transport layer of p–i–n planar configured devices. The cations induce thin 2D perovskite growth beneath the 3D perovskite to create a 2D/3D hybrid active layer. This 2D layer in turn acts as a template for the growth of relatively large grains compared to that of pure 3D perovskite films. This stems from the merging of grain boundaries. The hydrophobicity of the 2D/3D perovskite film consequently improves, as evidenced by a large contact angle of 93.1°, compared to 68.9° for the 3D perovskite film. Because there are fewer defects sourced from grain boundaries, the air‐processed 2D/3D perovskite devices yield a high power conversion efficiency of 15.02%, compared to 13.10% from 3D perovskite devices. When stored in moderately humid environment of 55% relative humidity, the 2D/3D devices exhibit longer stabilities, with 75% of their power conversion efficiencies maintained after 150 h, compared to a total loss in efficiency for 3D device in the same time frame.

A gradient grain‐sized (GGS) CsPbI₃ bilayer is developed to stabilize the α phase via a single‐step film‐deposition process. The perovskite solar cell based on the GGS CsPbI₃ bilayer shows an efficiency of 15.5% and operates stably for 1000 h under ambient conditions.

Abstract

The emerging inorganic CsPbI₃ perovskites are promising wide‐bandgap materials for application in tandem solar cells, but they tend to transit from a black α phase to a yellow δ phase in ambient conditions. Herein, a gradient grain‐sized (GGS) CsPbI₃ bilayer is developed to stabilize the α phase via a single‐step film deposition process. The spontaneously upward migration of (adamantan‐1‐yl)methanammonium (ADMA) based on the hot‐casting technique causes self‐assembly of the hierarchical morphology for the perovskite layers. Due to the strong steric effect of the surficial ADMA cation, a self‐assembly tiny grain‐sized CsPbI₃ layer is in situ formed at the surface site, which exhibits notably enhanced phase stability by its high surface energy. Meanwhile, a large grain‐sized CsPbI₃ layer is obtained at the bottom site with high charge mobility and low trap density of states, which benefits from the regulated growth rates by the interaction between ADMA and perovskites. The perovskite solar cell (PSC) based on the GGS CsPbI₃ bilayer shows an efficiency of 15.5% and operates stably for 1000 h under ambient conditions. This work confirms that redistributing the surface energy of perovskite films is a facile strategy to stabilize metastable PSCs without the cost of efficiency loss.

High‐performance semitransparent organic solar cells are achieved through combined design efforts on the formulation of near‐infrared ternary blends and optical control over photonic reflectors, which exhibit excellent features of power generation, they being see‐through, and infrared reflection.

Abstract

Clean energy production and saving play vital impacts on the sustainability of the global community. Herein, high‐performance semitransparent organic solar cells (ST‐OSCs) with excellent features of power generation, being see‐through, and infrared reflection of heat dissipation, with promising perspectives for building‐integrated photovoltaics (BIPVs) are reported. To simultaneously improve average visible transmittance (AVT) and power conversion efficiency (PCE), formally in a trade‐off relationship, of ST‐OSCs, new ternary blends with alloy‐like near‐infrared (NIR) acceptors are employed, which are effective to improve device efficiency while maintaining visible absorption unchanged, resulting in PCEs of 16.8% for opaque devices and 13.1% for semitransparent OSCs (AVT of 22.4% and infrared photon radiation rejection (IRR) of 77%). Further, multifunctional ST‐OSCs are realized via introducing simple, yet effective photonic reflectors, together with optical simulation, leading to not only perfect fitting of the visible transmittance peak (555 nm) to the photopic response of the human eye but also an excellent IRR of 90% (780–2500 nm), along with 23% AVT and over 12% PCE. This is thought to be the best‐performing multifunctional ST‐OSC with promising prospects as BIPVs in terms of power generation, heat dissipation, and being see‐through.

A method of device annealing including an indium tin oxide (ITO) layer is proposed, acheiving an efficiency of 12.6% for Cd‐alloyed Cu₂ZnSnS₄ thin‐film solar cells. The V _OC is increased by the reduction of both interface traps and deep‐level defects, and fill factor enhancement is based on the favorable band alignment (conduction band offset) and ITO improvement after postannealing.

Abstract

Kesterite Cu₂ZnSnS₄ is a promising photovoltaic material containing low‐cost, earth‐abundant, and stable semiconductor elements. However, the highest power conversion efficiency of thin‐film solar cells based on Cu₂ZnSnS₄ is only about 11% due to low open‐circuit voltage and fill factor mainly caused by antisite defects and unfavorable heterojunction interface. In this work, a postannealing procedure is proposed to complete a Cd‐alloyed Cu₂ZnSnS₄ device. The postannealing to complete the device significantly enhances the performance of the indium tin oxide and promotes the moderate interdiffusion of elements between the layers in the device. As a result of the diffusion of Cu, Zn, In, and Sn, the interfacial electron and hole densities are improved, leading to the achievement of a suitable band alignment for carrier transport. The postannealing also reduces the interface traps and deep‐level defects, contributing to decreased nonradiative recombination. Therefore, the open‐circuit voltage and fill factor are both improved, and an efficiency over 12% for pure sulfide‐based kesterite thin‐film solar cells is obtained.