Ligang Yuan

The involvement of guanidinium in perovskite bulk film and CH₃O-PEABr passivation on the perovskite surface synergistically suppresses the trap states. The charge carrier lifetimes of perovskite films increase by tenfold and fivefold to 981 ns and 8.02 µs at the crystal surface and in its bulk, respectively. The decreased nonradiative recombination loss translates to a record efficiency of 40.1%.

Abstract

Perovskite solar cells exhibit not only high efficiency under full AM1.5 sunlight, but also have great potential for applications in low-light environments, such as indoors, cloudy conditions, early morning, late evening, etc. Unfortunately, their performance still suffers from severe trap-induced nonradiative recombination, particularly under low-light conditions. Here, a holistic passivation strategy is developed to reduce traps both on the surface and in the bulk of micrometer-thick perovskite film, leading to a record efficiency of 40.1% under 301.6 µW cm⁻² warm light-emitting diode (LED) light for low-light solar-cell applications. The involvement of guanidinium into the perovskite bulk film and 2-(4-methoxyphenyl)ethylamine hydrobromide (CH₃O-PEABr) passivation on the perovskite surface synergistically suppresses the trap states. The charge carrier lifetimes of the perovskite film increase by tenfold and fivefold to 981 ns and 8.02 µs at the crystal surface and in its bulk, respectively. The decreased nonradiative recombination loss translates to a high open-circuit voltage (V _oc) of 1.00 V, a high short-circuit current (J _sc) of 152.10 µA cm⁻², and a fill factor (FF) of 79.52%. Note that this performance also stands as the highest among all photovoltaics measured under indoor light illumination. This work of trap passivation for micrometer-thick perovskite film paves a way for high-performance, self-powered IoT devices.

Europium (Eu) doped perovskite QD glass ceramic works as perfect scintillator because of high light yield, superior transparency, and hence significantly suppressed optical crosstalk, as well as the protection of glass matrix. Eventually the record-high imaging resolution of 15.0 lp mm⁻¹ is achieved, the radiation hardness is also significantly improved.

Abstract

All-inorganic perovskite quantum dots (QDs) CsPbX₃ (X = Cl, Br, and I) have recently emerged as a new promising class of X-ray scintillators. However, the instability of perovskite QDs and the strong optical scattering of the thick opaque QD scintillator film imped it to realize high-quality and robust X-ray image. Herein, the europium (Eu) doped CsPbBr₃ QDs are in situ grown inside transparent amorphous matrix to form glass-ceramic (GC) scintillator with glass phase serving as both matrix and encapsulation for the perovskite QD scintillators. The small amount of Eu dopant optimizes the crystallization of CsPbBr₃ QDs and makes their distribution more uniform in the glass matrix, which can significantly reduce the light scattering and also enhance the photoluminescence emission of CsPbBr₃ QDs. As a result, a remarkably high spatial resolution of 15.0 lp mm⁻¹ is realized thanks to the reduced light scattering, which is so far a record resolution for perovskite scintillator based X-ray imaging, and the scintillation stability is also significantly improved compared to the bare perovskite QD scintillators. Those results provide an effective platform particularly for the emerging perovskite nanocrystal scintillators to reduce light scattering and improve radiation hardness.

Herein, a semitransparent flexible MAPbBr₃ perovskite solar cell is demonstrated to be the roof of a greenhouse. It demonstrates a power conversion efficiency (PCE) of 7.67% with an average transmittance of ≈60% in the range of 540–760 nm.

Perovskite photovoltaics (PV) is an emerging thin-film solar energy technology that is advantageous over the currently dominant crystalline silicon PV in terms of its adjustable bandgap with sub-bandgap transparency, potential flexibility, and more rapid continuous roll-to-roll manufacturing, showing promise for unique niche applications. Herein, methylammioun lead tribromide (MAPbBr₃) is utilized in a semitransparent flexible solar cell with a transparent electrode using a sandwiched MoO₃/Au/MoO₃ (MAM) multilayer to harvest around 80% of the visible light region. Through design of the thickness of the MAM multilayer, the reflected light loss is significantly reduced, thereby improving the light transmittance in the visible light region to maximize the photosynthetic yield. The semitransparent flexible device exhibits a power conversion efficiency (PCE) of 7.67% (the highest efficiency of MAPbBr₃-based semitransparent flexible devices), and the opaque rigid MAPbBr₃ solar cell shows a PCE of 9.73% with a high open-circuit voltage of 1.629 V. Optical measurement demonstrates that the flexible cell without metal electrode shows over 77% transparency in the 540–1100 nm range, whereas the overall semitransparent cell shows an average transmittance of 60% in the 540–760 nm range, which is perfect for greenhouse vegetation to not only act as protective coverage but also provide practical output power.

Metal halide perovskite nanocrystal (PNC)/polymer nanocomposites that combine the unique optoelectronic properties of PNCs and outstanding stability, flexibility, and processability enabled by polymers are an appealing class of material with many promising applications. The state-of-the-art synthetic strategies and intriguing properties of PNC/polymer nanocomposites, as well as their wide-ranging applications in light emision, sensing, and energy conversion areas are summarized.

Abstract

Metal halide perovskite nanocrystals (PNCs) have recently garnered tremendous research interest due to their unique optoelectronic properties and promising applications in photovoltaics and optoelectronics. Metal halide PNCs can be combined with polymers to create nanocomposites that carry an array of advantageous characteristics. The polymer matrix can bestow stability, stretchability, and solution-processability while the PNCs maintain their size-, shape- and composition-dependent optoelectronic properties. As such, these nanocomposites possess great promise for next-generation displays, lighting, sensing, biomedical technologies, and energy conversion. The recent advances in metal halide PNC/polymer nanocomposites are summarized here. First, a variety of synthetic strategies for crafting PNC/polymer nanocomposites are discussed. Second, their array of intriguing properties is examined. Third, the broad range of applications of PNC/polymer nanocomposites is highlighted, including light-emitting diodes (LEDs), lasers, and scintillators. Finally, an outlook on future research directions and challenges in this rapidly evolving field are presented.

A dual-functional polymer is introduced into a [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) layer to simultaneously modify the PCBM electron transport layer (ETL) and passivate the surface defects in the perovskite. The hybrid ETL exhibits excellent electronic properties and the ability to suppress the ion migration in perovskite solar cells, leading to a high power conversion efficiency of 21.13% and long-term stability.

Herein, the use of the polymer poly([N, N ′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)) (PNDI-2T) as both a dopant in the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) electron transport layer (ETL) of inverted perovskite solar cells (PSCs) and a surface passivant on the perovskite layer is reported. The PNDI-2T doping is found to be crucial for improving the homogeneity of the ETL film with complete surface coverage, enhancing the electron mobility of the ETL, and promoting the energy level match between the perovskite and ETL, thereby significantly facilitating electron transport in the PSC devices. Furthermore, as a passivant, the PNDI-2T in the ETL tends to pin on the top surface of the perovskite layer via PbS coordination. The surface passivation is also beneficial for the suppression of ion migration and diffusion of metal species from the electrodes. In consequence, PSCs with the PCBM:PNDI-2T ETL reached an efficiency of 21.13% and retain 90% of their original performance after 860 h light soaking. This work will inspire new efforts to take advantage of multifunctional ETLs as a simple and effective method to enhance the performance and long-term stability of PSCs.

The design principle for lead-free perovskites and the progress of typical lead-free perovskite photodetectors are reviewed and discussed. The outlook for future research and applications is then explored.

Abstract

State-of-the-art photodetectors which apply hybrid perovskite materials have emerged as powerful candidates for next-generation light sensing. Among them, lead-based ones are the most popular beyond doubt on account of their unique and superior optoelectronic properties. Nevertheless, trade-off toward commercialization exists between nontoxicity and high performance, with the poor stability of lead-based perovskites, indicating that it is indispensable to substitute lead with nontoxic element meanwhile bringing about a comparable figure of merit of photodetectors and relatively long-term stability. Herein, recent advances in lead-free perovskite photodetectors are reviewed, analyzing the principle while designing new materials and highlighting some remarkable progress, which are comparable, even superior, to lead-based photodetectors. Furthermore, their potential strategy in optical communication, image sensing, narrowband photodetection, etc., is examined and a perspective on developing new materials and photodetectors with superior properties for more practical applications is provided.

Nature, Published online: 05 April 2021; doi:10.1038/s41586-021-03406-5

We developed a size effect that controls the crystallization of perovskite and enhances the passivation effect with g-C₃N₄ additive. The similarity in value of lattice constant and distance between double hydrogen binding sites affects crystallization. The combination allows g-C₃N₄ to cover tin-based perovskite, thus improves hydrophobicity and oxidation resistance of films and leads to splendid PCE of wearable device with excellent stability.

Abstract

Tin-based perovskite solar cells (PSCs) demonstrate a potential application in wearable electronics due to its hypotoxicity. However, poor crystal quality is still the bottleneck for achieving high-performance flexible devices. In this work, graphite phase-C₃N₄ (g-C₃N₄) is applied into tin-based perovskite as a crystalline template, which delays crystallization via a size-effect and passivates defects simultaneously. The double hydrogen bond between g-C₃N₄ and formamidine cation can optimize lattice matching and passivation. Moreover, the two-dimensional network structure of g-C₃N₄ can fit on the crystals, resulting an enhanced hydrophobicity and oxidation resistance. Therefore, the flexible tin-based PSCs with g-C₃N₄ realize a stabilized power conversion efficiency (PCE) of 8.56 % with negligible hysteresis. In addition, the PSCs can maintain 91 % of the initial PCE after 1000 h under N₂ environment and keep 92 % of their original PCE after 600 cycles at a curvature radius of 3 mm.

Publication date: August 2021

Source: Nano Today, Volume 39

Author(s): Lingbo Jia, Fanyang Huang, Honghe Ding, Chuang Niu, Yanbo Shang, Wanpei Hu, Xingcheng Li, Xin Yu, Xiaofen Jiang, Ruiguo Cao, Junfa Zhu, Guan-Wu Wang, Muqing Chen, Shangfeng Yang

A facile immersing and washing strategy (I‐method) is reported to prepare effective organic monomolecular layers (MLs) as hole transport layers (ML‐HTLs). The I‐method can largely reduce the process cost as well as realize batch preparation of ML‐HTLs. Perovskite solar cells based on ML‐HTLs show improved power conversion efficiency and stability.

Hole transport materials and their processing occupy at least one‐third of the cost of perovskite solar cells (PSCs), which leaves plenty of room to improve the process of device fabrication. Herein, a facile immersing and washing strategy (I‐method) is reported to prepare effective organic monomolecular layers (MLs) of poly[N ,N ′‐bis(4‐butylphenyl)‐N ,N ′‐bis(phenyl) benzidine] (polyTPD) as hole transport layers (ML‐HTLs) to construct cost‐effective planar inverted PSCs. The ML enables an enhanced wettability to perovskite precursors and thus results in the growth of compact and uniform perovskite films. In addition, the ML exhibits better energy‐level alignment with perovskite. Consequently, the ML‐polyTPD‐based PSCs deliver significantly enhanced power conversion efficiency (PCE) and reproducibility, as compared to that of pristine polyTPD based devices. The practical consumption of polyTPD during the I‐method is cut to the bone, with the cost of $0.8 for 1 m² substrate being achieved, which is 0.15% of that by S‐method. The developed I‐method is facile, and time‐ and cost‐saving with low requirement for facilities as well as with low temperature and solution processability. This strategy is cost‐effective to prepare ML‐HTLs for large‐area and flexible PSCs with competitive photovoltaic performance and enhanced reproducibility.

Here, a special method of 2D-MA₃Sb₂I₉ back surface field (BSF) is highlighted for efficient and stable perovskite solar cells (PSCs). MA₃Sb₂I₉ changes the MAPbI₃ surface to be more p-type and thus acts as a BSF to drive charge extraction. More importantly, strong chemical bonding of SbI prohibits ion diffusion, largely enhancing the thermal stability and long-term stability.

Abstract

In perovskite solar cells (PSCs), a defective perovskite (PVK) surface and cliff-like energy offset at the interface always slow down the charge extraction; meanwhile, interface ion diffusion causes oxidation of the metal electrode, inducing device instability. Here, the in situ grown 2D-(CH₃NH₂)₃Sb₂I₉ (MA₃Sb₂I₉) on the back surface of MAPbI₃ results in a more robust interface. MA₃Sb₂I₉ changes the MAPbI₃ surface to p-type and thus acts like a back surface field to drive charge extraction and suppress recombination, resulting in an obviously higher fill factor (FF) = 0.8 and power conversion efficiency (PCE) = 20.4% of SnO₂/MAPbI₃/MA₃Sb₂I₉/Spiro-OMeTAD (2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene) PSC than the pure MAPbI₃ device. More importantly, strong chemical bonding of SbI prohibits ion diffusion, largely enhancing the thermal stability and longtime stability. Here, special 2D-MA₃Sb₂I₉ constructs’ robust band alignment and chemical environment at the interface are highlighted for efficient and stable PSCs.

The interface passivation and performance enhancements of perovskite solar cell (PSCs) devices are realized by introducing few-layer nonmetallic element sulfur-doped graphite carbon nitride nanosheets in the SnO₂-based electron transport layer (ETL) at the first time, which is attributed to the enhanced electron mobility and conductivity of CNS-modified ETL, reduced interfacial trap state density, and improved crystallinity of perovskite film.

High-quality electron transport layer (ETL) is beneficial to improve the charge extraction and transport, which determines the performance of perovskite solar cells (PSCs). However, the unbalanced charge extraction and interface problems commonly occur in the tin oxide (SnO₂) ETL. Herein, the sulfur-doped graphite carbon nitride (CNS) nanosheets are prepared and utilized for modifying the SnO₂ ETL to fabricate high-performance PSCs. The CNS-modified SnO₂ ETL exhibits enhanced electron mobility and conductivity, and matched energy level with perovskite, which promotes the extraction and transport of charge carriers at the interface, and balances charge extraction with the hole transport layer. In addition, interfacial carrier recombination is significantly reduced through effective interface passivation of sulfur atoms in CNS with the undercoordinated lead ions in perovskite films. Meanwhile, the introduction of an interfacial control material CNS also contributes to improve the crystalline quality of perovskite films with increasing grain size and light absorption intensity. As a consequence, an outstanding improvement in power conversion efficiency (PCE) from 18.98% to 20.33% is achieved after introducing CNS into the SnO₂ ETL, as well as an enhancement in stability against humidity, retaining near 90% of the initial PCE after aging in the ambient atmosphere for 30 days.

Mixing chlorobenzene (CB) and H₂O in the perovskite precursor is an effective method to improve the direct contact between poly-TPD and the perovskite active layer. Inverted (p–i–n) perovskite solar cells based on the modified perovskite display efficient hole-interface charge transfer and suppression of the bulk and interfacial nonradiative recombination, thereby achieving an excellent power conversion efficiency of 22.1%.

Inverted perovskite solar cells (IPSCs) suffer from perishing interface contact due to the non-wetting hole-transport layer (HTL). Herein, the several classes of solvent to the perovskite precursor (the process is defined as solvent-additive engineering) for achieving an improvement in the interface contact between nonwetting HTL and active perovskite layer, suitably achieving improved hole-interface charge transfer, are mixed. Also, a high-quality perovskite layer with high crystallinity, large grain distribution, and flat surface morphology is obtained based on solvent-additive engineering, which affords a lower bulk and interface trap density. IPSCs with the modified perovskite layer show suppression of nonradiative recombination on the surface and in the bulk of the perovskite, thereby achieving an outstanding power conversion efficiency of 20.6%. In addition, IPSCs using a mixed-cation perovskite (FA_0.83Cs_0.07MA_0.13PbI_2.64Br_0.39) are also fabricated and a highest efficiency of 22.1%, visualizing the broad applicability of this method, is achieved. This simple, low-cost, and efficient solvent-additive strategy can solve interface contact problems and improve perovskite quality, thus potentially giving rise to other applications.

A templated growth approach, in which the crystallization of a 3D perovskite is guided by a dynamically dominant 2D structure, was established for the fabrication of a low-dimensional perovskite thin film with an out-of-plane orientation and a large grain size. The template growth is enabled by the reduced crystallization barrier of the 2D PEA₂SnI_4−x SCN _x intermediate.

Abstract

The manipulation of the dimensionality and nanostructures based on the precise control of the crystal growth kinetics boosts the flourishing development of perovskite optoelectronic materials and devices. Herein, a low-dimensional inorganic tin halide perovskite, CsSnBrI_2−x (SCN) _x , with a mixed 2D and 3D structure is fabricated. A kinetic study indicates that Sn(SCN)₂ and phenylethylamine hydroiodate can form a 2D perovskite structure that acts as a template for the growth of the 3D perovskite CsSnBrI_2−x (SCN) _x . The film shows an out-of-plane orientation and a large grain size, giving rise to reduced defect density, superior thermostability, and oxidation resistance. A solar cell based on this low-dimensional film reaches a power conversion efficiency of 5.01 %, which is the highest value for CsSnBr _x I_3−x perovskite solar cells. Furthermore, the device shows enhanced stability in ambient air.

High radiance and stable perovskite light emitting diodes are demonstrated by engineering the electron transport layer (ETL) and the use of formamidinium (FA) based perovskite. The optimal device shows a peak external quantum efficiency (EQE) of 11.4% at 330 mA cm⁻² and less than 10% EQE roll-off up to 770 mA cm⁻², with a half-life time over 475 h at 50 mA cm⁻².

Abstract

Although perovskite light emitting diodes (PeLEDs) have shown fast advances in external quantum efficiency (EQE), their operational stability is still low compared to other LED devices. Here, stable PeLEDs are demonstrated with high radiance primarily by using 6,6′-phenyl-C₆₁-butyric acid methyl ester (PCBM) and magnesium-doped Zinc oxide (ZnMgO) injection layers to reduce the driving voltage. Through different characterizations, it is revealed that the use of PCBM/ZnMgO electron injection layer can effectively mitigate Joule heating, block the migration of Al electrode towards perovskite layer as well as avoid the breakdown of main perovskite crystal structure under prolonged operation. Combining the PCBM/ZnMgO electron injection layer with a formamidinium-based perovskite light emitter, the optimal device shows an EQE of 11.4% at 330 mA cm⁻² and a radiance of 399 W Sr⁻¹ m⁻² at 3.1 V. The device remains above 50% of the maximum performance after operating for 525 and 118 h at constant current densities of 50 and 100 mA cm⁻², respectively. Thus, this work presents a substantial improvement in the stability of PeLEDs and the methods to consolidate this progress even further.

Publication date: 19 May 2021

Source: Joule, Volume 5, Issue 5

Author(s): Haibing Xie, Zaiwei Wang, Zehua Chen, Carlos Pereyra, Mike Pols, Krzysztof Gałkowski, Miguel Anaya, Shuai Fu, Xiaoyu Jia, Pengyi Tang, Dominik Józef Kubicki, Anand Agarwalla, Hui-Seon Kim, Daniel Prochowicz, Xavier Borrisé, Mischa Bonn, Chunxiong Bao, Xiaoxiao Sun, Shaik Mohammed Zakeeruddin, Lyndon Emsley

Nature Energy, Published online: 08 April 2021; doi:10.1038/s41560-021-00802-z