Ligang Yuan

Publication date: 15 February 2023

Source: Chemical Engineering Journal, Volume 454, Part 4

Author(s): Han Sol Yang, Eui Hyun Suh, Sung Hoon Noh, Jaemin Jung, Jong Gyu Oh, Kyeong Ho Lee, Dongwoon Lee, Jaeyoung Jang

A room-temperature molten salt dimethylamine acetate is developed as the solvent for precursor solutions, which also regulates the phase conversion process of the CsPbI₃ film. Consequently, 1.25 V of the open-circuit voltage and >21% power conversion efficiency are achieved, which is the record highest for CsPbI₃ perovskite solar cells reported so far.

Abstract

All-inorganic CsPbI₃ perovskite has emerged as an important photovoltaic material due to its high thermal stability and suitable bandgap for tandem devices. Currently, the cell performance of CsPbI₃ solar cells is mainly subject to a large open-circuit voltage (V _OC) deficit. Herein, a multifunctional room-temperature molten salt, dimethylamine acetate (DMAAc) is demonstrated, which not only directly acts as a solvent for precursor solutions, but also regulates the phase conversion process of the CsPbI₃ film for high-efficiency photovoltaics. DMAAc can stabilize the DMAPbI₃ structure and eliminate the Cs₄PbI₆ intermediate phase, which is easily spatially segregated. Meanwhile, a new homogeneous intermediate phase DMAPb(I,Ac)₃ is formed, which finally affords high-quality CsPbI₃ films. With this approach, the charge capture activity of defects in the CsPbI₃ film is significantly suppressed. Consequently, a V _OC of 1.25 V and >21% power conversion efficiency are achieved, which is the record highest reported thus far. This intermediate phase-regulation strategy is believed to be applicable to other perovskite material systems.

Three novel self-doped molecules named t-PyDIN, t-PyDINO and t-PyDINBr are developed as cathode interfacial materials for OSCs. The devices based on t-PyDINBr and t-PyDINO exhibit PCEs of 17.24 % and 17.56 %, respectively. Notably, the device based on t-PyDIN even reached a PCE of 18.25 %, which is improved by 51.3 % compared with that of the device without a cathode interfacial layer. This result is among the best efficiencies reported to date.

Abstract

Efficient cathode interfacial layers (CILs) are becoming essential elements for organic solar cells (OSCs). However, the absorption of commonly used cathode interfacial materials (CIMs) is either too weak or overlaps too much with that of photoactive materials, hindering their contribution to the light absorption. In this work, we demonstrate the construction of highly efficient CIMs based on 2,7-di-tert-butyl-4,5,9,10-pyrene diimide (t-PyDI) framework. By introducing amino, amino N-oxide and quaternary ammonium bromide as functional groups, three novel self-doped CIMs named t-PyDIN, t-PyDINO and t-PyDINBr are synthesized. These CIMs are capable of boosting the device performances by broadening the absorption, forming ohmic contact at the interface of active layer and electrode, as well as facilitating electron collection. Notably, the device based on t-PyDIN achieved a power conversion efficiency of 18.25 %, which is among the top efficiencies reported to date in binary OSCs.

Fast synthesis of α-phase crystallized mixed-cation perovskite powder assisted with moisture in ambient air is developed. The significant role of moisture in introducing the solvation effect and the facet orientation change of PbI₂ is demonstrated by a combined experimental and theoretical investigation. Perovskite solar cells based on α-phase mixed-cation perovskite powder deliver an impressive PCE of 24.07 %.

Abstract

Phase-pure crystallised perovskite is considered an excellent precursor for fabricating high-stability perovskite films with minimal defects. However, currently available protocols for synthesising crystallised perovskites must be conducted in an inert atmosphere or in the presence of an organic solvent as the reaction medium, which hinders mass production. Here, we report the fast synthesis of α-phase-crystallised perovskite powder assisted by moisture in ambient air. Moisture can promote the reaction between PbI₂ and organic salts and facilitate complete phase transition, as demonstrated in a joint experimental and theoretical study. Perovskite solar cells with a power conversion efficiency of 24.07 % were achieved using phase-pure crystallised perovskite powder as the precursor. This ambient-air-compatible method opens new vistas to reproducible high-quality precursors for large-scale photovoltaic applications.

Publication date: 1 January 2023

Source: Chemical Engineering Journal, Volume 451, Part 3

Author(s): Kai-Chi Hsiao, Yen-Fu Yu, Ching-Mei Ho, Meng-Huan Jao, Yu-Hsiang Chang, Shih-Hsuan Chen, Yin-Hsuan Chang, Wei-Fang Su, Kun-Mu Lee, Ming-Chung Wu

A hole transport material (BDT-DPA-F) is designed, and it can assemble into a fibril network, showing an obviously improved hole mobility, a decreased energy disorder and high scalability. The perovskite solar cells based on BDT-DPA-F without any dopant obtain promising power conversion efficiencies of 23.12 % (certified 22.48 %) for small-area devices (0.062 cm²) and 20.17 % for large-area modules (15.64 cm²).

Abstract

Dopant-free organic hole transport materials (HTMs) remain highly desirable for stable and efficient n-i-p perovskite solar cells (pero-SCs) but rarely succeed. Here, we propose a molecular assembly strategy to overcome the limited optoelectronic properties of organic HTMs by precisely designing a linear organic small molecule BDT-DPA-F from the atomic to the molecular levels. BDT-DPA-F can assemble into a fibril network, showing an obviously improved hole mobility and decreased energy disorder. The resultant pero-SCs showed a promising efficiency of 23.12 % (certified 22.48 %), which is the highest certified value of pero-SCs with dopant-free HTMs, to date. These devices also showed a weak-dependence of efficiency on size, enabling a state-of-the-art efficiency of 22.50 % for 1-cm² device and 20.17 % for 15.64-cm² module. For the first time, the pero-SCs based on dopant-free HTMs realized ultralong stabilities with T ₈₀ lifetimes over 1200 h under operation or thermal aging at 85 °C.

An effective molecular engineering is demonstrated to simultaneously improve the performance and stability of perovskite devices. This strategy allows to obtain desired optoelectronic and chemical properties for novel nonspiro-based hole conductors, which leads to the fabrication of solar cells displaying remarkable efficiency of 21.2% with excellent stability under the harsh aging conditions.

Abstract

Despite considerable development in performance, both poor operational stability and high costs associated with hole conductors such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) and Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) of perovskite solar cells (PSCs) need to be addressed by the research community. Here, two nonspiro hole transporting materials (HTMs), namely HTM-1 and HTM-2, are designed and straightforwardly synthesized exhibiting remarkable electrochemical properties and hole mobilities. In particular, the PSC based on the methoxy derivative (HTM-2) exhibits a remarkable efficiency of 21.2% (stabilized efficiency of 20.8%), which is superior to the benchmark HTM spiro-OMeTAD (stabilized efficiency of 20.4%). These results establish that the molecular design is effective in improving the performance of PSCs. Importantly, these two HTMs show admissible long-term stability under different harsh conditions such as thermal stress up to 85 °C, high humidity level of 60% ± 10%, and continuous illumination over 1000 h. These insights allow correlating the impact of molecular design on optoelectronic properties of nonspiro-based hole conductors with the overall device performance.

A systematic understanding of the mechanism of photon propagation and carrier kinetics of semitransparent perovskite solar cells (ST-PSCs) is critical for the development of high-performance ST-PSCs. In this paper, the key factors affecting the high light utilization of ST-PSCs are deeply discussed from the theoretical analysis, and the recent advances from the view of photon propagation management and carrier kinetics regulation of ST-PSCs are summarized, which provides guidance for promoting the rapid development and further commercialization of ST-PSCs.

Abstract

Semitransparent perovskite solar cells (ST-PSCs) are ideal candidates for building-integrated photovoltaics (BIPV) and tandem solar cells (TSCs) owing to their tunable bandgap and high visible transparency. The best power conversion efficiency (PCE) of ST-PSCs is close to 15% with an average visible transmittance of over 20%, which still lags far behind the PCE of normal opaque PSCs. This can be attributed to the poor light utilization efficiency (LUE) of ST-PSCs. Herein, the pivotal routes for maximizing LUE of ST-PSCs in terms of photon propagation management and carrier kinetics regulation are systematically rationalized. First, the fundamental theoretical analyses on optical processes and electronic properties are provided. Then, insights on photon propagation management measures and carrier kinetics regulation strategies are provided. Furthermore, a summary of the promising commercial application of ST-PSCs in BIPV and TSCs is provided. Finally, the main progress of ST-PSCs is briefly summarized, and the directions for the commercialization of ST-PSCs are proposed.

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.

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