Chen Weijie

In this work, the mixed spacer cations 2D perovskite (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ films are obtained by employing two typical spacer cations, 1,4-butanediamonium (BDA²⁺) usually for Dion-Jacobson phase and 2-phenylethylammonium (PEA⁺) for Ruddlesden-Popper phase. The device with (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ film achieves the power conversion efficiency of 17.21% with excellent thermal and humidity stability.

Abstract

In this article, two different types of spacer cations, 1,4-butanediamonium (BDA²⁺) and 2-phenylethylammonium (PEA⁺) are co-used to prepare the perovskite precursor solutions with the formula of (BDA)_{1- a} (PEA₂) _a MA₄Pb₅X₁₆. By simply mixing the two spacer cations, the self-assembled polycrystalline films of (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ are obtained, and BDA²⁺ is located in the crystal grains and PEA⁺ is distributed on the surface. The films display a small exciton binding energy, uniformly distributed quantum wells and improved carrier transport. Besides, utilizing mixed spacer cations also induces better crystallinity and vertical orientation of 2D perovskite (BDA)_0.8(PEA₂)_0.2MA₄Pb₅X₁₆ films. Thus, a power conversion efficiency (PCE) of 17.21% is achieved in the optimized perovskite solar cells with the device structure of ITO/PEDOT:PSS/Perovskite/PCBM/BCP/Ag. In addition, the complementary humidity and thermal stability are obtained, which are ascribed to the enhanced interlayer interaction by BDA²⁺ and improved moisture resistance by the hydrophobic group of PEA⁺. The encapsulated devices are retained over 95% or 75% of the initial efficiency after storing 500 h in ambient air under 40 ± 5% relative humidity or 100 h in nitrogen at 60 °C.

The highest efficiency of 20.39% is obtained for perovskite solar cells based on modified ZnO without annealing and antisolvent process. The perovskite devices exhibit unprecedented environmental stability owing to efficient decreased organic ligands on ZnO surface.

Abstract

Even though ZnO is commonly used as the ETL in the perovskite solar cell (PSC), the reactivity of perovskite deposited thereupon limits its performance. Herein, an ethylene diamine tetraacetic acid-complexed ZnO (E-ZnO) is successfully developed as a significantly improved electron selective layer (ESLs) in perovskite device. It is found that E-ZnO exhibits higher electron mobility and better matched energy level with perovskite compared to ZnO. In addition, in order to eliminate the proton transfer reaction at the ZnO/perovskite interface, a high quality perovskite film fabrication process that requires neither annealing nor antisolvent is developed. By taking advantages of both E-ZnO and the new process, the highest efficiency of 20.39% is obtained for PSCs based on E-ZnO. Moreover, the efficiency of unencapsulated PSCs with E-ZnO retains 95% of its initial value exposed in an ambient atmosphere after 3604 h. This work provides a feasible path toward high performance of PSCs, and it is believed that the present work will facilitate transition of perovskite photovoltaics in flexible and tandem devices since the annealing- and antisolvent-free technology.

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.

Publication date: August 2021

Source: Nano Energy, Volume 86

Author(s): Yilin Chang, Xiangwei Zhu, Lingyun Zhu, Yuheng Wang, Chen Yang, Xianrong Gu, Yixiao Zhang, Jianqi Zhang, Kun Lu, Xiangnan Sun, Zhixiang Wei

Publication date: August 2021

Source: Nano Energy, Volume 86

Author(s): Muhammad Fahim, Irum Firdous, Weihai Zhang, Walid A. Daoud

Publication date: August 2021

Source: Nano Energy, Volume 86

Author(s): Xinxing Liu, Zizheng Wu, Xiaoxiao Fu, Liting Tang, Jianmin Li, Junbo Gong, Xudong Xiao

Publication date: August 2021

Source: Nano Energy, Volume 86

Author(s): LiangLe Wang, Md. Shahiduzzaman, Ersan Y. Muslih, Masahiro Nakano, Makoto Karakawa, Kohshin Takahashi, Koji Tomita, Jean Michel Nunzi, Tetsuya Taima

The main role of triplets as a solar cell efficiency loss mechanism in DRCN5T systems is elucidated. Despite the high efficiencies obtained with DRCN5T, it creates a considerable large number of triplets. It is also found that these triplets decrease the charge population through triplet-charge annihilation. Moreover, a method is proposed to probe this process present in fullerene and non-fullerene blends.

Abstract

Organic photovoltaics (OPV) are close to reaching a landmark 20% device efficiency. One of the proposed reasons that OPVs have yet to attain this milestone is their propensity toward triplet formation. Herein, a small molecule donor, DRCN5T, is studied using a variety of morphology and spectroscopy techniques, and blended with both fullerene and non-fullerene acceptors. Specifically, grazing incidence wide-angle X-ray scattering and transient absorption, Raman, and electron paramagnetic resonance spectroscopies are focused on. It is shown that despite DRCN5T's ability to achieve OPV efficiencies of over 10%, it generates an unusually high population of triplets. These triplets are primarily formed in amorphous regions via back recombination from a charge transfer state, and also undergo triplet-charge annihilation. As such, triplets have a dual role in DRCN5T device efficiency suppression: they both hinder free charge carrier formation and annihilate those free charges that do form. Using microsecond transient absorption spectroscopy under oxygen conditions, this triplet-charge annihilation (TCA) is directly observed as a general phenomenon in a variety of DRCN5T: fullerene and non-fullerene blends. Since TCA is usually inferred rather than directly observed, it is demonstrated that this technique is a reliable method to establish the presence of TCA.

Direct photogeneration of free charge carriers enabled by remarkably low exciton binding energies is demonstrated in the state-of-the-art nonfullerene acceptor of Y6 by a joint experimental and theoretical study. This results in efficient charge generation under small interfacial energy offsets in the high-efficiency nonfullerene organic solar cells.

Abstract

Organic solar cells (OSCs) with nonfullerene acceptors (NFAs) exhibit efficient charge generation under small interfacial energy offsets, leading to over 18 % efficiency for the single-junction devices based on the state-of-the-art NFA of Y6. Herein, to reveal the underlying charge generation mechanisms, we have investigated the exciton binding energy (E _b) in Y6 by a joint theoretical and experimental study. The results show that owing to strong charge polarization effects, Y6 has remarkable small E _b of −0.11–0.15 eV, which is even lower than perovskites in many cases. Moreover, it is peculiar that the photoluminescence is enhanced with temperature, and the energy barrier for separating excitons into charges is evidently lower than the thermal energy according to the temperature dependence of photoluminescence, manifesting direct photogeneration of charge carriers enabled by weak E _b in Y6. Thus, charge generation in NFA-based OSCs shows little dependence on interfacial driving forces.

Stable and efficient CsPbI₃ perovskite light-emitting diodes (PLEDs) are demonstrated by resurfacing perovskite with the aid of inorganic ligands (KI). The resurfaced perovskites show a 7× higher phase stability and higher thermal conductivity than in films with organic ligands. The PLEDs exhibit a record-high external quantum efficiency (EQE) of ≈23 % and a 100-fold improvement in the operating stability compared to previous EQE devices.

Abstract

The all-inorganic nature of CsPbI₃ perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI₃ films; however, these strategies—including strain and doping—are based on organic-ligand-capped perovskites, which prevent perovskites from forming the close-packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI₃ QD films with superior phase stability and increased thermal transport. The atomic-ligand-exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI-exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half-lifetime of 10 h (luminance of 200 cd m⁻²) and an operating stability that is 6× higher than that of control devices.

A strategy for broadband photodetection of X-ray, ultraviolet, and near-infrared photons is proposed. A class of lanthanide–perovskite nanocrystals is developed by in situ crystallization of perovskite nanocrystals on the surface of mSiO₂-coated lanthanide-doped upconversion nanocrystals. Such nanotransducers are further used to implement flexible X-ray imaging with a spatial resolution up to 20 lp mm⁻¹.

Abstract

Solution-processed metal-halide perovskites hold great promise in developing next-generation low-cost, high-performance photodetectors. However, the weak absorption of perovskites beyond the near-infrared spectral region posts a stringent limitation on their use for broadband photodetectors. Here, the rational design and synthesis of an upconversion nanoparticles (UCNPs)–perovskite nanotransducer are presented, namely UCNPs@mSiO₂@MAPbX₃ (X = Cl, Br, or I), for broadband photon detection spanning from X-rays, UV, to NIR. It is demonstrated that, by in situ crystallization and deliberately tuning the material composition in the lanthanide core and perovskites, the nanotransducers allow for a high stability and show a wide linear response to X-rays of various dose rates, as well as UV/NIR photons of various power densities. The findings provide an opportunity to explore the next-generation broadband photodetectors in the field of high-quality imaging and optoelectronic devices.

An efficient polythiophene-based organic solar cell (OSC) is demonstrated based on a fluorinated polythiophene donor with deep highest occupied molecular orbital (HOMO) level and appropriate miscibility with the acceptor. With further interfacial modification by a fullerene self-assembled monolayer, a record power conversion efficiency (PCE) of 13.65% for polythiophene-based OSCs is achieved with the device processed from nonhalogenated solvent.

Abstract

Benefiting from low cost and simple synthesis, polythiophene (PT) derivatives are one of the most popular donor materials for organic solar cells (OSCs). However, polythiophene-based OSCs still suffer from inferior power conversion efficiency (PCE) than those based on donor–acceptor (D–A)-type conjugated polymers. Herein, a fluorinated polythiophene derivative, namely P4T2F-HD, is introduced to modulate the miscibility and morphology of the bulk heterojunction (BHJ)-active layer, leading to a significant improvement of the OSC performance. The Flory–Huggins interaction parameters calculated from the surface energy and differential scanning calorimetry results suggest that P4T2F-HD shows moderate miscibility with the popular nonfullerene acceptor Y6-BO (2,2′-((2Z,2′Z)-((12,13-bis(2-butyloctyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2′,3′:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile), while poly(3-hexylthiophene) (P3HT) is very miscible with Y6-BO. As a result, the P4T2F-HD case forms desired nanoscale phase separation in the BHJ film while the P3HT case forms a completely mixed BHJ film, as revealed by transmission electron microscopy (TEM) and grazing-incidence wide-angle X-ray scattering (GIWAXS). By optimizing the cathode interface and the morphology of the P4T2F-HD:Y6-BO films processed from nonhalogenated solvents, a new record PCE of 13.65% for polythiophene-based OSCs is demonstrated. This work highlights the importance of controlling D/A interactions for achieving desired morphology and also demonstrates a promising OSC system for potential cost-effective organic photovoltaics.

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

Publication date: 21 July 2021

Source: Joule, Volume 5, Issue 7

Author(s): Zeng Chen, Xu Chen, Ziyan Jia, Guanqing Zhou, Jianqiu Xu, Yuexia Wu, Xinxin Xia, Xufeng Li, Xuning Zhang, Chao Deng, Yuan Zhang, Xinhui Lu, Weimin Liu, Chunfeng Zhang, Yang (Michael) Yang, Haiming Zhu

Publication date: 8 July 2021

Source: Chem, Volume 7, Issue 7

Author(s): Albertus A. Sutanto, Pietro Caprioglio, Nikita Drigo, Yvonne J. Hofstetter, Ines Garcia-Benito, Valentin I.E. Queloz, Dieter Neher, Mohammad Khaja Nazeeruddin, Martin Stolterfoht, Yana Vaynzof, Giulia Grancini

Ultrathin crystals of the 1D organic–inorganic perovskite [C₇H₁₀N]₃[BiCl₅]Cl featuring covalent bonds only in one direction are exfoliated down to single layers. The unique 1D–2D structure enables self-trapped excitons with white-light emission and an extremely strong shift of the emission energy as a result of the thickness dependence of the exciton self-trapping.

Abstract

Low-dimensional organic–inorganic perovskites synergize the virtues of two unique classes of materials featuring intriguing possibilities for next-generation optoelectronics: they offer tailorable building blocks for atomically thin, layered materials while providing the enhanced light-harvesting and emitting capabilities of hybrid perovskites. This work goes beyond the paradigm that atomically thin materials require in-plane covalent bonding and reports single layers of the 1D organic–inorganic perovskite [C₇H₁₀N]₃[BiCl₅]Cl. Its unique 1D–2D structure enables single layers and the formation of self-trapped excitons, which show white-light emission. The thickness dependence of the exciton self-trapping causes an extremely strong shift of the emission energy. Thus, such 2D perovskites demonstrate that already 1D covalent interactions suffice to realize atomically thin materials and provide access to unique exciton physics. These findings enable a much more general construction principle for tailoring and identifying 2D materials that are no longer limited to covalently bonded 2D sheets.