Reduced Charge Recombination Research Articles

Effect of bismuth iodide ([formula omitted]) interfacial layer with different HTL’s in FAPI based perovskite solar cell – SCAPS – 1D study

In this paper, we numerically investigated the effect of Bismuth iodide (BiI3) interfacial layer with different hole transport layer (HTL) candidates (including Spiro-OMeTAD,Cu2O,CuI,CuAlO2,CuSbS2,SrCu2O2,CuSCN,PTAA,P3HT) in FAPI based perovskite (i.e., FA0.85Cs0.15PbI0.85Br0.153 solar cells using Solar cell simulator capacitance software (SCAPS-1D). Our results reveal that the addition of a thin BiI3 layer at the interface between the Perovskite active layer and the HTL efficiently improves hole extraction by defect passivation (i. e., reducing charge recombination and ion migration), which in turn enhances device performance compared to a typical reference architecture. The final optimized device photovoltaic parameters with interfacial layer confirm that the Cu-based HTL’s, especially Cu2O(PCE=24.07%), and SrCu2O2 (PCE=23.91%) HTL’s are more suitable for the FA0.85Cs0.15PbI0.85Br0.153 solar cells than other HTL alternatives, including Spiro-OMeTAD due to higher hole mobility and the valence-band offset alignment between Perovskite/HTL interface. Also, the influence of several metal electrodes Ag,Cr,Cu,Au,Ni,Pt is carefully studied with and without the BiI3 interlayer. It is demonstrated that the energy band misalignment between the HTL and the metallic top electrode restricts charge collection, which is directly associated with low work functions. As a consequence, high work function electrodes such as Au,Ni, and Pt have to be preferred in the presence or absence of the interlayer. The last section addresses the influence of the active layer, BiI3 interlayer thicknesses on device performance and also the effect of parasitic resistances (Rseries and Rshunt) were studied. From this analysis, BiI3 interfacial layer seems highly beneficial for improving the performance of experimental perovskite solar cells.

Dimensionality Control of SnO2 Films for Hysteresis-Free, All-Inorganic CsPbBr3 Perovskite Solar Cells with Efficiency Exceeding 10.

The all-inorganic cesium lead bromide (CsPbBr3) perovskite solar cells (PSCs) have attracted considerable interest because of their outstanding environmental stability and low manufacturing cost. However, the state-of-the-art mesoscopic titanium dioxide (TiO2) electron-transporting layers (ETLs) always present low electron mobility, are destructive to perovskites under ultraviolet light illumination, as well as possess high sintering temperature. Nanostructured tin dioxide (SnO2) is a promising electron-transporting material for high-efficiency PSCs due to matching energy-level alignment with the perovskite layer, improved optical transparency, high electron mobility, excellent photostability, and low-temperature processing. Furthermore, rapid but poorly controlled perovskite crystallization makes it difficult to scale up planar PSCs for industrial applications. To address this issue, we adopt a dimensional SnO2 ETL to change the surface wettability for uniform perovskite coverage over large areas and the growth of large-sized CsPbBr3 grains, resulting in a maximum grain size of 1.65 μm. Moreover, the dimensional SnO2 ETL could increase the interfacial contact area between the CsPbBr3 layer and the ETL and enhance the electronic contact for efficient electron extraction to suppress or to eliminate the notorious hysteresis behavior. As expected, a power conversion efficiency (PCE) of 9.51% with an almost hysteresis-free phenomenon is achieved through dimensionality control of SnO2 films attributed to the remarkably enhanced light harvesting, accelerated electron extraction, diminished defect density, and reduced charge recombination. Upon further interfacial modification with graphene quantum dots (GQDs), the PSC based on the two-dimensional SnO2 ETL achieves a champion PCE of 10.34% due to the improved energy-level alignment at the device interface. Moreover, the best all-inorganic CsPbBr3 PSC free of encapsulation retains 93% of initial efficiency over 10 days at 80% relative humidity. This work provides an effective dimensionality control strategy for optimized charge transportation and enlarged perovskite grain size to make stable and efficient all-inorganic CsPbBr3 PSCs.

Effective Dark Current Suppression for High-Detectivity Organic Near-Infrared Photodetectors Using a Non-Fullerene Acceptor.

Near-infrared organic photodetectors (NIR OPDs) have attracted considerable attention because of their inherent advantages such as a tailorable light absorption property, low-cost fabrication, compatibility with flexible substrates, and room-temperature operation. In particular, the development of NIR detection between 900 and 950 nm is crucial for noise-free communication in ambient environments. In this work, we demonstrate high-detectivity NIR OPDs at 900-950 nm by employing a non-fullerene acceptor (ITIC) used with an NIR-absorbing conjugated polymer (PNIR) for bulk heterojunction (BHJ), which significantly suppressed dark current. Systemic characterizations including electrical, structural, and morphological analyses revealed that ITIC effectively reduces charge recombination during the operation of the OPDs under NIR illumination, resulting in a dark current reduction and high detectivity of over 3.2 × 1011 Jones at 900-950 nm. The results presented here demonstrate that utilizing a non-fullerene acceptor for BHJ-type NIR OPDs is evidently a strategic approach for the simultaneous achievement of the low dark current and high-detectivity of NIR OPDs.

Layer-by-Layer Processed Ternary Organic Photovoltaics with Efficiency over 18.

Obtaining a finely tuned morphology of the active layer to facilitate both charge generation and charge extraction has long been the goal in the field of organic photovoltaics (OPVs). Here, a solution to resolve the above challenge via synergistically combining the layer-by-layer (LbL) procedure and the ternary strategy is proposed and demonstrated. By adding an asymmetric electron acceptor, BTP-S2, with lower miscibility to the binary donor:acceptor host of PM6:BO-4Cl, vertical phase distribution can be formed with donor-enrichment at the anode and acceptor-enrichment at the cathode in OPV devices during the LbL processing. In contrast, LbL-type binary OPVs based on PM6:BO-4Cl still show bulk-heterojunction like morphology. The formation of the vertical phase distribution can not only reduce charge recombination but also promote charge collection, thus enhancing the photocurrent and fill factor in LbL-type ternary OPVs. Consequently, LbL-type ternary OPVs exhibit the best efficiency of 18.16% (certified: 17.8%), which is among the highest values reported to date for OPVs. The work provides a facile and effective approach for achieving high-efficiency OPVs with expected morphologies, and demonstrates the LbL-type ternary strategy as being a promising procedure in fabricating OPV devices from the present laboratory study to future industrial production.

Insights into the tribo-/pyro-catalysis using Sr-doped BaTiO3 ferroelectric nanocrystals for efficient water remediation

Abstract Ferroelectric materials have multiple characteristics in ferroelectric, piezoelectric, pyroelectric properties, which provide an attractive prospect for simultaneously harvesting multiple energy sources for catalytic applications. However, the crucial challenge for wastewater purification lies in the development of ferroelectric materials with improved functions and the design of advanced oxidation processes. Herein, Sr0.3Ba0.7TiO3 (SBT-0.3) nano-catalysts modified by PVP surfactant could significantly promote water recovery efficiency from the rhodamine B (RhB), which is as high as 98% by simultaneously collecting two types of energy sources of mechanical friction and temperature fluctuation from the natural environment for tribo-/pyro-catalysis under dark conditions. It was found that the samples containing PVP surfactant show significantly improved performance in the separation of charge carriers in comparison with those without PVP surfactant. The permanent polarization in SBT-0.3, coupled with the piezo-/pyro-potential, could generate internal field and therefore reduce charge recombination. It also helps to absorb charged species from the dye solution, which favors the reaction with active oxygen to cause the cleavage and breakdown of organic molecules. The mechanism of RhB decomposition mediated by SBT-0.3 ferroelectric is also discussed. This work favors us to in-depth understanding for the tribo-/pyro-catalysis and hence proposes a new strategy to improve the water purification efficiency of ferroelectric nanocrystals.

Tri‐Brominated Perovskite Film Management and Multiple‐Ionic Defect Passivation for Highly Efficient and Stable Solar Cells

High‐quality perovskite films with low imperfections, high hole mobility, and matching energy levels play a crucial role in enhancing performance of perovskite solar cells (PSCs) without hole‐transporting materials (HTMs). Herein, it is demonstrated that the incorporation of a stable tetra‐bisphenol A (TBBPA) with diphenyl ring, polybromides, and hydroxyl groups additive into a perovskite film can simultaneously manipulate the crystal growth and passivate the defects through coordination interaction between the functional group (OH, Br) and the unsaturated halogen and metal ions (Br−, Cs+, and Pb2+), resulting in a reduced grain boundary as well as imperfection and increased hole mobility of the CsPbBr3 perovskite film. In addition, the valence band of a perovskite film with TBBPA additive is shifted upward to approach the work function of the carbon electrode, thereby improving the energy level alignment. Consequently, a significantly boosted charge extraction and reduced charge recombination of the carbon‐based HTM‐free CsPbBr3 PSCs is obtained after incorporating the TBBPA additive, yielding a maximum power conversion efficiency of up to 9.82% of the optimized device. Furthermore, the champion PSC without encapsulation displays a remarkable thermal and moisture stability after being kept in ambient air for 720 h at 85 °C and 85% relative humidity, respectively.

Functional ZnO/TiO2 Bilayer as Electron Transport Material for Solution‐Processed Sb2S3 Solar Cells

Electron transport materials (ETMs) are considered a keystone component of third‐generation solar cells. Among the alternative ETM, metal oxide bilayers have attracted increasing attention due to their easy processing and tunability of cascade energy alignment. Herein, a metal oxide bilayer that combines ZnO and TiO2 compact films (ZnO/TiO2) is implemented as ETM for solution‐processed Sb2S3 planar solar cells. The bilayer ETM achieves the highest photovoltaic performance when compared with devices based on single ETM. Thus, the optimized device based on ZnO/TiO2 ETM yields a champion efficiency of 5.08% with an open‐circuit voltage of 0.58 V and a current density of 16.17 mA cm−2. Using surface photovoltage, electrochemical impedance spectroscopy, and current density–voltage analyses, it is demonstrated that the use of ZnO/TiO2 promotes charge injection, decreases series resistance and shutting paths, and leads to the reduction of charge recombination at the ETM/Sb2S3 interface.

Perovskite with inhomogeneous composition: Presence of the Cl-rich layer improves the device performance

A perovskite compositional difference was engineered at the perovskite/electron transport layer (ETL) interface. The devices with inhomogeneous perovskite composition achieve the best power conversion efficiency of 16.1% under the optimal conditions, compared with 12.5% for the control, and the device stability is also improved. Further characterizations indicate that the performance enhancement is due to the larger perovskite grain size with less pinholes, the improved charge extraction at the perovskite/ETL interface, and the reduced charge recombination. This modification effect is induced by constructing an additional Cl-rich layer on bottom of the primary CH3NH3PbI3 film.

Multifunctional potassium hexafluorophosphate passivate interface defects for high efficiency perovskite solar cells

The interface modulation between perovskite and carrier-transport layers via an appropriate chemical bond is an effective way to achieve the promoted carrier extraction and the reduced charge recombination for high-efficiency perovskite solar cells (PSCs). Here, a multifunctional material potassium hexafluorophosphate (KPF6) is employed as an effective interface material between SnO2 quantum dots (QDs) and perovskite. At perovskite side, KPF6 could react with perovskite through the strong hydrogen bonds between PF6− group and organic cations, which could re-orientate or redistribute the organic cation groups. Meanwhile, KPF6 could react with SnO2 QD through the strong ionic bonds between PF6− group and Sn4+/Sn2+ at the SnO2 QD side, which could passivate the interface defects to suppress the non-radiative recombination for the improved electron-transferring. Consequently, a champion PCE over 21% comes from the PSCs with 0.5 mg/ml KPF6 treated the SnO2 QD/perovskite interface, and the devices maintain ~90% of initial PCEs after 720-h storage in dry air.

Significance of nanostructure morphologies in photoelectrochemical water splitting cells: A brief review

The main component in photoelectrochemical (PEC) water splitting technology is the semiconductor, which its electronic structure has an essential effect on the final performance of the cell. Morphology plays a significant role in the electronic properties of semiconductors. The relationship between the electron and optical properties of nanostructures and their surface morphology is a subject that is less addressed in scientific papers. This review attempts to detail the impact of morphology on nanostructures' properties, such as light absorption and charge carrier transport. Creating a direct path for electron transport, reducing charge recombination, and increasing light scattering are some of the things that are directly related to the surface morphology of nanostructures. The present review aims to provide general information about synthesized nanostructures and their advantages and disadvantages to help readers create new ideas and innovate in this field.

Cesium-Doped Ti <sub>3</sub>C <sub>2</sub>T <sub>x</sub> MXene for Efficient and Thermally Stable Perovskite Solar Cells

Ti3C2Tx MXenes have been shown to be a promising candidate for use in various applications. Herein, we prepared functionalized Ti3C2Tx MXene nanosheets doped with cesium (Cs) and introduced them into lead iodide (PbI2) precursor solution for perovskite solar cells (PSCs) through a two-step deposition method. Our theoretical and experimental analysis revealed that Cs plays an important role in improving the perovskite crystallization and thus leading to enlarged crystal grains, long-lived carrier lifetimes, and reduced charge recombination as compared to the devices fabricated without and with undoped Ti3C2Tx MXene. PSCs integrated with Cs doped Ti3C2Tx MXene delivered a high photovoltaic efficiency of up to 21.57% with excellent thermal stability. The incorporation of Cs-Ti3C2Tx paves the way to further improve the photovoltaic performance and thermal stability of PSCs.

Atomic-level localization of π-electrons in defect engineered tri-s-triazine units for increased photocatalytic hydrogen generation of polymeric carbon nitride

N defects in tri-s-triazine units can localize π electrons to reduce charge recombination and act as active sites, thus improving the efficiency of photocatalytic hydrogen production.

Cube-like mixed-phases TiO2 mesocrystalline hollow boxes from in situ topotactic transformation for highly efficient dye-sensitized solar cells

The cube-like TiO2 mesocrystalline hollow boxes (TiO2-MHBs) are fabricated by a topotactic transformation method. TiO2-MHBs consist of one-dimensional nanorod-like rutile TiO2 combined with anatase TiO2. The ordering of TiO2-MHBs is in favor of efficient electron transport. TiO2-MHBs with mesoporous structure show excellent light scattering performance. Dye-sensitized solar cell with TiO2-MHBs light scattering overlayer exhibits an 18.3% increment of cell efficiency (9.51%) compared with the TiO2 nanoparticles film cell (8.04%). The improved photovoltaic performance is attributed to its unique crystallographic property and highly porous structure, which can enhance light scattering capability, quicken electron transport and electrolyte diffusion, and reduce charge recombination.

Ti3C2 2D MXene: Recent Progress and Perspectives in Photocatalysis.

In 2011, with the successful isolation of Ti3C2, a door of 2D layered MXene has been opened and received growing attention from researchers. MXene refers to a family of two-dimensional (2D) materials made up of atomic layers of the transition metal, carbide, nitrides, or carbonitrides. Given the large surface area, adjustable surface terminal groups, and excellent conductivity of MXene, it has shown exciting potential in photocatalysis, energy conversion, and many other fields. Among many 2D MXene, Ti3C2 was the most studied for its availability, low cost, facile modification procedure, and outstanding electronic properties. In previous investigations, Ti3C2 has shown huge potential in the photocatalysis area. Ti3C2 in a photocatalysis system can enhance the separation of photoinduced electrons and holes, reduce charge recombination, and thus improve the photocatalysis performance in many systems. To adjust the performance of Ti3C2 in different applications, the properties of Ti3C2 including morphology, structures, and stability are tunable by different post-processing method in the hybridized materials. In this review, an all-around understanding of the fabrication and modification methods of Ti3C2 and their connection to photocatalytic applications of Ti3C2 MXene based materials are presented. Moreover, a summary and our perspectives of Ti3C2 are given for further investigation.

Hollow 3D TiO2 sub-microspheres as an electron transporting layer for highly efficient perovskite solar cells

In today's optoelectronic devices, particularly perovskite solar cells (PSCs), morphological engineering and microscopic architecture of metal oxide semiconducting materials are of great significance for enhanced charge collection, photonic structuring, and optical enhancement optimization. Herein, three-dimensional hollow TiO2 sub-microspheres (3D-HTS) composed of anatase nanocrystals are synthesized using the hydrothermal method and used as a novel and efficient type of electron transport layer (ETL) for high-performance mesoscopic PSC. The TiO2 sub–microsphere-based film features a 3D interconnected structure with tunable film thicknesses and pore sizes. The PSC based on such sub-microsphere films results in an outstanding power conversion efficiency (PCE) of 18.01% that is 28% greater than the TiO2 nanoparticles (TNPs) ETL-based counterpart (PCE = 14.08%). The better efficiency of the sub–microsphere-made PSC device can be ascribed to the considerably improved charge collection, charge-transport, and light-harvesting capabilities. These valuable properties are because of the titania macropores that allow effective infiltration of the perovskite precursor for efficient light absorption, with reduced charge recombination and enhanced charge-transport through the sub-microspheres architecture. This work shows a practical and straightforward method for preparing 3D metal oxide–based electrodes for superior photovoltaic devices.

Ternary Organic Semiconductor Blend for High Photovoltaic Performance Under Both Indoor and Outdoor Operating Conditions

Ternary blend in Organic Photovoltaics (OPVs) have been known as a way to increase performance in both low light intensity and AM 1.5G conditions. We have conducted a comparative study on 2 Donors:1 Acceptor (2D:1A) blends and 1 Donor:2 Acceptors (1D:2A) blends; 1D:2A blends have the higher performance and thermal stability than 2D:1A blends. In particular, non-fullerene acceptor (NFA) used for the 1D:2A blends have a good effect on packing property and crystallinity. The 1D:2A with optimized morphology reduced charge recombination on various irradiation conditions while the efficiency of 2D:1A devices depends on the fluorescence resonance energy transfer mechanism. The synergistic effect of 1D:2A blend with NFAs secures better efficiency and sustainable photoelectric properties under both indoor and outdoor operation conditions. Our analysis of the experiments reveals that NFA optimizes the arrangement of molecules to build more efficient ternary bulk heterojunctions in 1D:2A blends. Finally, the optimized ternary OPVs show effectively high power conversion efficiency of over 25% in both 200 lux and 1000 lux light–emitting diode conditions and present new opportunities in various practical applications.

Tailoring organic bulk-heterojunction for charge extraction and spectral absorption in CsPbBr3 perovskite solar cells

All-inorganic CsPbBr3 perovskite solar cells (PSCs) are promising candidates to balance the stability and efficiency issues of organic-inorganic hybrid devices. However, the large energy barrier for charge transfer and narrow spectral response are still two challenging problems for performance improvement. We present here an organic bulk-heterojunction {poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT: PCBM)} photoactive layer to boost the charge extraction and to widen the spectral absorption, achieving an enhanced power conversion efficiency up to 8.94% by optimizing the thickness of P3HT: PCBM photoactive layer, which is much higher than 6.28% for the pristine CsPbBr3 device. The interaction between the carbonyl group in PCBM and unsaturated Pb atom in the perovskite surface can effectively passivate the defects and reduce charge recombination. Furthermore, the coupling effect between PCBM and P3HT widens the spectral response from 540 to 650 nm for an increased short-circuit current density. More importantly, the devices are relatively stable over 75 days upon persistent attack by 70% relative humidity in air condition. These advantages of high efficiency, excellent long-term stability, cost-effectiveness and scalability may promote the commercialization of inorganic PSCs.

Ordered array structures for efficient perovskite solar cells

AbstractIn the past few years, metal halide perovskite solar cells (PSCs) have attracted widespread attention in the photovoltaic field, and their power conversion efficiency has rapidly exceeded 25%. Among the adopted effective strategies to realize the high efficiency, the introduction and utilization of ordered array structure in the PSCs are particularly prominent, which can simultaneously enhance light harvesting efficiency and carrier transport properties by manipulating the light paths (reflection, scattering, extraction, and propagation) and constructing direct charge transport paths. The full utilization of sunlight contributes to high short‐circuit current density (Jsc), and strong carriers transport is favorable for high charge collection and reducing charge recombination. Moreover, for flexible PSCs, ordered array structured device can be greatly relaxed during bending, thereby suppressing the formation of cracks in PSCs. Herein, this article focuses on the ordered array structure design, reviews the recent research progress of the ordered array structures in PSCs, and provides some promising perspectives for further improvement.

A simple engineering strategy with side chain liquid crystal polymers in perovskite absorbers for high efficiency and stability

Abstract Accomplishing a superior perovskite layer with better morphology, enhanced efficiency, and improved stability is one of the great challenges to researchers. In present work, we incorporated various side chain liquid crystal polymers (SCLCP) as dopants into the perovskite precursor to attain high efficiency and long-term stability of the perovskite solar cells (PSCs). Incorporation of SCLCP increases the grain size of the crystalline perovskite film by controlled solvent evaporation, decreased the grain boundaries and reduced charge recombination, which decelerates the material degradation. With the SCLCP doping, the PSC power conversion efficiency was expressively enhanced from 17.8% (non-doped) to 19.01% for the doped perovskite film with much improved stability. Furthermore, the atomic force microscopy measurements showed a better surface roughness for doped film by effective passivation of the perovskite grain surfaces. Field emission scanning electron microscope also showed better morphology with reduced grain boundaries. Especially, the SCLCP act as bridge between the crystal grains for efficient charge transfer from perovskite layer towards the electrode, which would moderately illustrate the increased efficiency and stability.

Development of AgFeO2/rGO/TiO2 Ternary Composite Photocatalysts for Enhanced Photocatalytic Dye Decolorization

Dyestuff is one of the most widely released pollutants into the environment. Many approaches have been considered to deal with the dye removal from polluted water such as adsorption, ultrafiltration, osmosis, solvent extraction and photocatalytic degradation. The photocatalytic degradation process is one of the most beneficial, economical and environmentally friendly ways to degrade the organic pollutants from wastewater. In this study, an efficient ferrite-based photocatalyst, AgFeO2/rGO/TiO2 was successfully developed using simple deposition and reflux method. Physical, chemical and structural properties were analyzed by using XRD, FTIR Raman and PL spectroscopy. The efficiency of photocatalyst was investigated for the decolorization of methyl blue (MB) dye and activity was measured through UV-vis spectroscopy. The effect of parameters like pH, concentrations of MB dye, and loading of silver ferrite (AgFeO2) was investigated. The study depicted that the properties of TiO2 were improved due to addition of silver ferrite and reduced graphene oxide (rGO). The 2.5% AgFeO2/rGO/TiO2 exhibited the highest efficiency and completely degraded the 50 ppm of MB dye in 30 min. The parametric study revealed that dye decolorization is faster in a neutral solution than in basic and acidic medium. The higher performance of the photocatalyst was attributed to the reduced charge recombination and improved optical properties. Thus, AgFeO2/rGO/TiO2 can be a potential composite for photocatalytic dye degradation and other photocatalytic applications under UV-Visible light irradiations.