Ligang Yuan

A technique of sequential passivation with acetylacetone (ACAC) and ethylenediamine (EDA) was proposed. The ACAC treatment can enlarge the grain size, and the EDA treatment stabilizes the perovskite against oxidation. A 13.0 % efficiency with improved stability was reported, which is one of the top efficiencies and stabilities for tin halide perovskite-based solar cells.

Abstract

Lead-free tin perovskite solar cells (PKSCs) have attracted tremendous interest as a replacement for toxic lead-based PKSCs. Nevertheless, the efficiency is significantly low due to the rough surface morphology and high number of defects, which are caused by the fast crystallization and easy oxidization. In this study, a facile and universal posttreatment strategy of sequential passivation with acetylacetone (ACAC) and ethylenediamine (EDA) is proposed. The results show that ACAC can reduce the trap density and enlarge the grain size (short-circuit current (J _sc) enhancement), while EDA can bond the undercoordinated tin and regulate the energy level (open-circuit voltage (V _oc) enhancement). A promising 13 % efficiency is achieved with better stability. In addition, other combinations of diketones or amines are selected, with similar effects. This study provides a universal strategy to enhance the crystallinity and passivate defects while fabricating stable PKSCs with high efficiency.

The potentiality of interfaced structures between halide perovskites is predicated on the vast tunable space of perovskites, the ease with which to tailor perovskite semiconducting properties and the prospect to inject new functions. This article reviews recent advances on the perovskite–perovskite interfaced structures with a view to informing their rational design for optoelectronic devices.

Abstract

The tsunami of research on halide perovskites over the last decade is sparked by the unexpected revelation of their singular properties, creating a new field of perovskite optoelectronics with great achievements. Soon recognized is the importance of perovskite–perovskite (pe–pe) interfaced structures with coherent interfaces on account of the ease with which to tailor perovskite semiconducting properties, and the prospect to inject new functions and boost device performance. There have been prominent developments in the pe–pe interfaced structures concerning their innovative construction strategies, distinctive properties, and interesting optoelectronic applications. This article provides an overview of recent advances on the pe–pe interfaced structures with a view to informing their rational design and guiding the improvement of the derivate devices. It begins with introduction of the structures, energy levels, band alignments, and ion migration pertaining to the pe–pe interfaced structures. Next, five synthetic approaches are systematically presented. Then, theories, simulations, and characterizations of the interfaced structures are discussed. This is followed by highlighting the distinctive applications of the pe–pe interfaced structures in solar cells, detectors, and light-emitting diodes. Finally, the review is concluded by comprehensively summing up the key points covered and pointing out promising research directions along the line for future endeavors.

Lead acetate is introduced into the precursor to improve the α-phase stability of CsPbI₂Br, and the dopant-free PM6 is employed as hole transport layer to further optimize the charge transport, which collaboratively contribute to a power conversion efficiency of 33.68% for the indoor photovoltaic cell, along with a remarkable open-circuit voltage of 1.15 V, testing under a 1000 lux light-emitting diode illumination.

Abstract

All-inorganic CsPbI₂Br perovskite has attracted great attention due to the stable crystal structure and moisture resistance, and its 1.91 eV bandgap is close to the optimal bandgap of indoor artificial light sources, making it be the best candidate for the indoor photovoltaics (IPVs) to power a wide range of internet of things related electronic devices. Herein, we report on the preparation of CsPbI₂Br with α-phase and the improvement of its phase stability by adding lead acetate in the CsPbI₂Br precursor. A series of dopant-free conjugated polymers (P3HT, PBDB-T, and PM6) with different highest occupied molecular orbital energy levels are introduced as hole transport layers for building IPV devices. The PM6 based devices having better energy alignment with perovskite demonstrate best indoor photovoltaic performance, giving a remarkable open-circuit voltage of 1.15 V and high fill factor of 81.86% under 1000 lux (330 µW cm⁻²) light-emitting diode illumination, and finally realizing a decent power conversion efficiency of 33.68%. Our findings suggest that collaboratively optimize the CsPbI₂Br layer and hole transport layer is an effective approach to realize high performance IPVs.

Polar species modification (PSM) is employed to reduce the defect capturing probability by strengthening the defect dielectric screening effect via increasing the dielectric constant of a perovskite film. The introduction of F₃EAI fills the vacancy defects at surface and also produces a hydrophobic umbrella with high resistance to humidity. PSM realizes a power conversion efficiency of 20.5% for CsPbI₃ perovskite solar cells.

Abstract

Nonradiative losses caused by defects are the main obstacles to further advancing the efficiency and stability of perovskite solar cells (PSCs). There is focused research to boost the device performance by reducing the number of defects and deactivating defects; however, little attention is paid to the defect-capture capacity. Here, upon systematically examining the defect-capture capacity, highly polarized fluorinated species are designed to modulate the dielectric properties of the perovskite material to minimize its defect-capture radius. On the one hand, fluorinated polar species strengthen the defect dielectric-screening effect via enhancing the dielectric constant of the perovskite film, thus reducing the defect-capture radius. On the other, the fluorinated iodized salt replenishes the I-vacancy defects at the surface, hence lowering the defect density. Consequently, the power-conversion efficiency of an all-inorganic CsPbI₃ PSC is increased to as high as 20.5% with an open-circuit voltage of 1.2 V and a fill factor of 82.87%, all of which are among the highest in their respective categories. Furthermore, the fluorinated species modification also produces a hydrophobic umbrella yielding significantly improved humidity tolerance, and hence long-term stability. The present strategy provides a general approach to effectually regulate the defect-capture radius, thus enhancing the optoelectronic performance.

Nature, Published online: 01 September 2022; doi:10.1038/s41586-022-05268-x

Vacancy-ordered double perovskite Cs₂ZrCl₆ is employed to fabricate large-area flexible X-ray scintillator screens. Joint experiment–theory characterizations indicate the broadband emission of Cs₂ZrCl₆ originates from the triplet emission of self-trapped excitons. The thermally activated delayed fluorescence feature of Cs₂ZrCl₆ provides a large Stokes shift and supports luminescence collection. The flexible scintillator screen achieves high-quality imaging of non-flat and dynamic objects.

Abstract

Flexible scintillator screens with environmental stability, high sensitivity, and low cost have emerged as candidates for X-ray imaging applications. Here, a large-scale and cost-efficient solution synthesis of the vacancy-ordered double perovskite Cs₂ZrCl₆, which is characterized by thermal activation delayed fluorescence (TADF) dominated by triplet emission under X-ray irradiation, is demonstrated. The large Stokes shift and efficient luminescence collection of TADF effectively ensure the light outcoupling efficiency. Further, flexible X-ray scintillator screens with an area of 400 cm² are prepared using poly(dimethylsiloxane) (PDMS) as the carrier, exhibiting excellent scintillation properties with light yields as high as 49 400 photons MeV⁻¹, spatial resolutions up to 18 lp mm⁻¹ and detection limits as low as 65 nGy s⁻¹. Finally, the high-quality imaging results of non-planar and dynamic objects by such screens are demonstrated. It is believed that the explored Cs₂ZrCl₆@PDMS flexible scintillator screens would offer a big step toward expanding the application range of scintillators in different environments.

Designed SiO₂@Ag core−shell particles with the surface plasmon resonance (SPR) wavelength at the near-infrared range are incorporated into perovskite solar cell devices. The embedding plasmons can interact with the active layer at the near-band edge via light scattering and electric field enhancement. Therefore, due to superior light utilization and carrier extraction, the corresponding incident-photon-to-current efficiency (IPCE) of the devices can be enlarged.

Abstract

Plasmonic perovskite solar cells (PSCs) using core−shell type plasmonic particles are designed, which possess the plasmon resonance in the near-infrared range. This can selectively strengthen the interaction of the perovskite layer with low-energy photons. The mesoporous PSCs employing the plasmonic particles have delivered a 10%–15% enhancement of external quantum efficiency in the plasmonic resonance range. This surface-plasmonic effect has been analyzed using complementary techniques, including selective wavelength excitation and time-dependent photoluminescence. It is shown that the metal-based core−shell-type plasmonic structures in PSCs optimize the scattering and absorption of incident light and the dynamics of photogenerated carriers. Furthermore, both optical and electronic effects increase the power conversion efficiency of PSCs from 17.49% to 19.88%, paving a way toward controlling the thickness of the photoactive layer for advanced devices such as tandem solar cells.

The preparation of perovskite solar cells by vacuum thermal evaporation processes has advantages in reproducibility, scalability, extendable applications, safety, and toxicity. In this review, materials and methods utilized for vacuum-processed perovskite solar cells are discussed, including precursor materials, the effect of the interlayer, and various deposition methods.

Perovskite solar cells (PSCs) based on inexpensive organic−inorganic hybrid semiconductors are considered a promising next-generation solar cell technology. For PSC commercialization, the further development of efficient and scalable fabrication methods is essential. To date, solution-based methods have been widely studied due to simplicity and cost-effectiveness. Despite the advantages, it is still necessary for developing vacuum-based methods as the alternative methods due to reproducibility and uniformity with in a large area. However, it is insufficiently studied for a systematic understanding of vacuum-based methods. To give helpful insight for understanding vacuum-based methods for PSC commercialization, this review introduces the precursor and charge transporting materials with the various preparation methods for vacuum-processed PSCs.

Small amounts of bromide incorporation in the triple cation tin-based perovskite solar cells enhance the vertical orientation of the perovskite film as well as suppress the tin oxidation in the film, resulting in a high power conversion efficiency (10.12%) with outstanding stability.

Tin-halide perovskite solar cells (THPSCs) are attractive in the photovoltaic field as promising candidates to address the issue of potential lead toxicity and approach the theoretical efficiency limit in lead-halide perovskite photovoltaics. Nevertheless, THPSCs suffer from fast crystallization, low defect tolerance, mismatched energy levels, as well as severe oxidation from Sn²⁺ to Sn⁴⁺, leading to the low performance of devices. Herein, bromide is incorporated in the PEA_0.15EA_0.15FA_0.70SnI_1−X Br _X perovskite precursor, which produces 2D/3D hybrid cations tin-halide perovskite films with highly vertical oriented crystallization, favorable band-level alignment, and suppressed tin oxidation. This leads to the decrease of trap density and charge recombination losses and the enhancement of charge carrier extraction in THPSCs. Consequently, the power conversion efficiency of the optimal THPSC (X = 0.30) surges to 10.12% in contrast to 7.13% of the control device (X = 0.00), along with a nearly eliminated current–voltage hysteresis. Furthermore, bromine-incorporated THPSCs exhibit outstanding light soaking and humidity stability. These results are also in good agreement with the density functional theory calculations. This compositional engineering with Br could become a promising approach for improving the efficiency and stability of THPSCs.

Orderly oxidation of CsPbI₂Br film in moist air leads to more efficient defect passivation in film by grain boundary oxidation, and higher hole extraction efficiency in device via the energy band coupling between CsPbI₂Br and oxidation product CsPbIBr₂. The champion cell achieves an efficiency of 15.27%, and a certified efficiency of 14.7%, which is a record efficiency for CsPbI₂Br C-PSCs.

Abstract

Large energy loss (E _loss) caused by defect-assisted recombination makes the photovoltaic performance of carbon-based perovskite solar cells (C-PSCs) inferior to that of metal-electrode ones. Herein, the influence of environmental factors (moisture and oxygen) on defect management during re-annealing process of CsPbI₂Br crystalline films is systematically studied. Density functional theory and experimental results indicate that moisture in the air can significantly reduce the oxidation kinetics of crystalline films, resulting in orderly oxidation. Concomitantly, the oxidation decomposition products PbO and CsPbIBr₂ are enriched at grain boundaries, passivating surface defects efficiently. Simultaneously, energy band coupling between CsPbI₂Br and CsPbIBr₂ improves the hole extraction efficiency. The photovoltage of corresponding C-PSCs is increased from 1.05 to 1.32 V, indicating a reduced E _loss derived from orderly oxidation strategy. Correspondingly, the champion cell achieves an efficiency of 15.27%, and a certified efficiency of 14.7%, which is a new record efficiency for CsPbI₂Br C-PSCs.

Donor alloy strategy is proposed to tune chare transfer (CT) state erergy and thus E _loss for boosting organic solar cells (OSCs) efficiency. Together with optimal morphology, ternary OSCs deliver an outstanding efficiency of 19.22% with significantly improved open-circuit voltage (V _oc) of 0.910 V, the highest value for over 19% efficiency OSCs.

Abstract

The large energy loss (E _loss) is one of the main obstacles to further improve the photovoltaic performance of organic solar cells (OSCs), which is closely related to the charge transfer (CT) state. Herein, ternary donor alloy strategy is used to precisely tune the energy of CT state (E _CT) and thus the E _loss for boosting the efficiency of OSCs. The elevated E _CT in the ternary OSCs reduce the energy loss for charge generation (ΔE _CT), and promote the hybridization between localized excitation state and CT state to reduce the nonradiative energy loss (ΔE _nonrad). Together with the optimal morphology, the ternary OSCs afford an impressive power conversion efficiency of 19.22% with a significantly improved open-circuit voltage (V _oc) of 0.910 V without sacrificing short-cicuit density (J _sc) and fill factor (FF) in comparison to the binary ones. This contribution reveals that precisely tuning the E _CT via donor alloy strategy is an efficient way to minimize E _loss and improve the photovoltaic performance of OSCs.

This article reviews the experimental and theoretical research of the thermal transport properties of halide perovskites since 2016. The microscopic behaviors of phonons are discussed along with the nonphononic descriptions. Also, the recent trends of the halide perovskites for thermal-related applications are presented.

Abstract

Halide perovskites have emerged as promising candidates for various applications, such as photovoltaic, optoelectronic and thermoelectric applications. The knowledge of the thermal transport of halide perovskites is essential for enhancing the device performance for these applications and improving the understanding of heat transport in complicated material systems with atomic disorders. In this work, the current understanding of the experimentally and theoretically obtained thermal transport properties of halide perovskites is reviewed. This study comprehensively examines the reported thermal conductivity of methylammonium lead iodide, which is a prototype material, and provides theoretical frameworks for its lattice vibrational properties. The frameworks and discussions are extended to other halide perovskites and derivative structures. The implications for device applications, such as solar cells and thermoelectrics, are discussed.

A new family of non-centrosymmetric hybrid Ge-based bromide perovskites are reported, showing second harmonic generation (SHG) responses. The largest SHG signal from CH₃NH₃GeBr₃ is likely due to the perferable alignment of the polar cation with the lone pair electrons of Ge²⁺ along the [111] direction.

Abstract

Ge-based hybrid perovskite materials have demonstrated great potential for second harmonic generation (SHG) due to the geometry and lone-pair induced non-centrosymmetric structures. Here, we report a new family of hybrid 3D Ge-based bromide perovskites AGeBr₃, A=CH₃NH₃ (MA), CH(NH₂)₂ (FA), Cs and FAGe_0.5Sn_0.5Br₃, crystallizing in polar space groups. These compounds exhibit tunable SHG responses, where MAGeBr₃ shows the strongest SHG intensity (5×potassium dihydrogen phosphate, KDP). Structural and theoretical analysis indicate the high SHG efficiency is attributed to the displacement of Ge²⁺ along [111] direction and the relatively strong interactions between lone pair electrons of Ge²⁺ and polar MA cations along the c-axis. This work provides new structural insights for designing and fine-tuning the SHG properties in hybrid metal halide materials.

Publication date: 1 January 2023

Source: Chemical Engineering Journal, Volume 451, Part 3

Author(s): Yansen Sun, Shuo Yang, Zhenyu Pang, Haipeng Jiang, Shaohua Chi, Xiaoxu Sun, Lin Fan, Fengyou Wang, Xiaoyan Liu, Maobin Wei, Lili Yang, Jinghai Yang

Publication date: 1 January 2023

Source: Chemical Engineering Journal, Volume 451, Part 3

Author(s): Yoseob Chung, Kyeong Su Kim, Jae Woong Jung

Nature Energy, Published online: 29 August 2022; doi:10.1038/s41560-022-01102-w

A synergistic bulk passivation and interface modification strategy is developed for the fabrication of high-quality tin–lead mixed perovskite films (1.27 eV) and efficient solar devices by blade-coating. Owing to the significantly suppressed nonradiative charge recombination, the prepared solar cells give a high efficiency of 19.06% with an impressive open-circuit voltage of 0.837 V.

Thin films of tin–lead alloyed perovskites are drawing growing attention, mainly owing to their tunable bandgaps in delivering efficient single- and multi-junction photovoltaic devices. The rapid efficiency advancement of Sn–Pb perovskite devices has been dependent primarily on improving the crystal quality of perovskite films via retarding oxidation of Sn²⁺. Herein, it is demonstrated that in addition to obtaining high-quality Sn–Pb perovskite thin films, reducing nonradiative recombination losses at interfaces is equally important for realizing efficient solar cells. An aromatic amine is first introduced to passivate the grain boundary in printed Sn–Pb perovskite films, which boosts the open-circuit voltage (V _OC) of the solar devices from 700 to 766 mV. Further enhancement of the V _OC to 814 mV and finally to 837 mV is realized by forming a 2D/3D-layered heterojunction and doping the hole extraction layer with a polyelectrolyte, respectively, benefiting from the largely suppressed nonradiative recombination losses at interfaces. Eventually, the mixed Sn–Pb perovskite devices with a bandgap of ≈1.27 eV yield a high efficiency of 19.06% and in parallel show improved shelf and light-soaking stability.

Modulation of film formation kinetics has paved the way for developing deep-blue emissive quasi-2D perovskites. A universal synthetic strategy, potentially applicable to various material systems, is introduced to narrow the width distribution of perovskite quantum wells. The controlled and simultaneous evaporation of solvent and antisolvent is key.

Abstract

Solution-processed quasi-2D perovskites contain multiple quantum wells with a broad width distribution. Inhomogeneity results in the charge funneling into the smallest bandgap components, which hinders deep-blue emission and accelerates Auger recombination. Here, a synthetic strategy applied to a range of quasi-2D perovskite systems is reported, that significantly narrows the quantum well dispersity. It is shown that the phase distribution in the perovskite film is significantly narrowed with controlled, simultaneous evaporation of solvent and antisolvent. Modulation of film formation kinetics of quasi-2D perovskite enables stable deep-blue electroluminescence with a peak emission wavelength of 466 nm and a narrow linewidth of 14 nm. Light emitting diodes using the perovskite film show a maximum luminance of 280 cd m^–2 at an external quantum efficiency of 0.1%. This synthetic approach will serve in producing new materials widening the color gamut of next-generation displays.

New synthesized non-conjugated polyelectrolyte is introduced as an interfacial layer between the charge-transport layer and perovskite absorbent, which significantly reduce both bulk and interfacial nonradiative recombination losses, but also aligns the interface's energy level. The modified perovskite solar cells show a power conversion efficiency of 24.4% (open-circuit voltage 1.21 V) with negligible hysteresis and superior operational stability.

Abstract

Suppressing nonradiative recombination at the interface between the organometal halide perovskite (PVK) and the charge-transport layer (CTL) is crucial for improving the efficiency and stability of PVK-based solar cells (PSCs). Here, a new bathocuproine (BCP)-based nonconjugated polyelectrolyte (poly-BCP) is synthesized and this is introduced as a “dual-side passivation layer” between the tin oxide (SnO₂) CTL and the PVK absorber. Poly-BCP significantly suppresses both bulk and interfacial nonradiative recombination by passivating oxygen-vacancy defects from the SnO₂ side and simultaneously scavenges ionic defects from the other (PVK) side. Therefore, PSCs with poly-BCP exhibits a high power conversion efficiency (PCE) of 24.4% and a high open-circuit voltage of 1.21 V with a reduced voltage loss (PVK bandgap of 1.56 eV). The non-encapsulated PSCs also show excellent long-term stability by retaining 93% of the initial PCE after 700 h under continuous 1-sun irradiation in nitrogen atmosphere conditions.

A strain modulation strategy to constrain phase segregation in a wide-bandgap perovskite absorber by reinforcing the energy barrier for ion migration is reported. With compressive strain, the single-junction devices yield one of smallest voltage deficits of 440 mV. Moreover, the resulting perovskite/silicon tandem solar cells achieve a champion efficiency of 26.95% with improved light stability at open-circuit.

Abstract

Perovskite/silicon tandem solar cells are promising to penetrate photovoltaic market. However, the wide-bandgap perovskite absorbers used in top-cell often suffer severe phase segregation under illumination, which restricts the operation lifetime of tandem solar cells. Here, a strain modulation strategy to fabricate light-stable perovskite/silicon tandem solar cells is reported. By employing adenosine triphosphate, the residual tensile strain in the wide-bandgap perovskite absorber is successfully converted to compressive strain, which mitigates light-induced ion migration and phase segregation. Based on the wide-bandgap perovskite with compressive strain, single-junction solar cells with the n–i–p layout yield a power conversion efficiency (PCE) of 20.53% with the smallest voltage deficits of 440 mV. These cells also maintain 83.60% of initial PCE after 2500 h operation at the maximum power point. Finally, these top cells are integrated with silicon bottom cells in a monolithic tandem device, which achieves a PCE of 26.95% and improved light stability at open-circuit.

An ultrathin hybrid hole transporting layer employing NiO_x/[2-(9H-carbazol-9-yl) ethyl]phosphonic acid enables complete and uniform coverage on fully textured indium tin oxide (ITO)/silicon surface with pyramid structures of 2–5 µm sizes. As a result of the depleted shunt pathways between ITO and perovskite top cell, a certified record efficiency—28.84%—is achieved on perovskite/silicon tandem solar cells with fully textured, production-line compatible bottom silicon wafers.

Abstract

Perovskite/silicon tandem solar cells are promising avenues for achieving high-performance photovoltaics with low costs. However, the highest certified efficiency of perovskite/silicon tandem devices based on economically matured silicon heterojunction technology (SHJ) with fully textured wafer is only 25.2% due to incompatibility between the limitation of fabrication technology which is not compatible with the production-line silicon wafer. Here, a molecular-level nanotechnology is developed by designing NiO_x/2PACz ([2-(9H-carbazol-9-yl) ethyl]phosphonic acid) as an ultrathin hybrid hole transport layer (HTL) above indium tin oxide (ITO) recombination junction, to serve as a vital pivot for achieving a conformal deposition of high-quality perovskite layer on top. The NiO_x interlayer facilitates a uniform self-assembly of 2PACz molecules onto the fully textured surface, thus avoiding direct contact between ITO and perovskite top-cell for a minimal shunt loss. As a result of such interfacial engineering, the fully textured perovskite/silicon tandem cells obtain a certified efficiency of 28.84% on a 1.2-cm² masked area, which is the highest performance to date based on the fully textured, production-line compatible SHJ. This work advances commercially promising photovoltaics with high performance and low costs by adopting a meticulously designed HTL/perovskite interface.