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Publication date: August 2020

Source: Nano Energy, Volume 74

Author(s): Hyeon Seok Lee, Min Kyu Kim, Seong Ryul Pae, Daehan Kim, HyeJi Seo, Passarut Boonmongkolras, Issam Gereige, Steve Park, Byungha Shin

Publication date: August 2020

Source: Nano Energy, Volume 74

Author(s): Qing Guo, Ji Lin, Haiqin Liu, Xingliang Dong, Xia Guo, Long Ye, Zaifei Ma, Zheng Tang, Harald Ade, Maojie Zhang, Yongfang Li

Publication date: August 2020

Source: Nano Energy, Volume 74

Author(s): Kohei Nishimura, Muhammad Akmal Kamarudin, Daisuke Hirotani, Kengo Hamada, Qing Shen, Satoshi Iikubo, Takashi Minemoto, Kenji Yoshino, Shuzi Hayase

Publication date: August 2020

Source: Nano Energy, Volume 74

Author(s): Lisha Xie, Zhiyuan Cao, Jianwei Wang, Aili Wang, Shurong Wang, Yuying Cui, Yong Xiang, Xiaobin Niu, Feng Hao, Liming Ding

Three chlorinated thiophene–based donor polymers are characterized and their devices based on each nonfullerene acceptors are fabricated and optimized. During the shelf life test without encapsulation, an abnormal decrease in the efficiency is observed in both P(Cl)(F  = 0.5) and P(F‐Cl). However, the P(Cl) device exhibits long‐term stability. To understand this, the correlation between crystallinity and miscibility is systematically studied.

Nonfullerene organic solar cells (NFOSCs) have proven to have greater potential in terms of efficiency than fullerene‐based OSCs. However, the heterogeneity of nonfullerene acceptors (NFAs)‐based blend morphology is complex, making it difficult to understand, especially as its optimization requires that compatibility among the molecules be considered. Herein, P(Cl)(F  = 0.5) is newly synthesized with a type of terpolymer to increase compatibility with NFAs relative to that of conventional polymers. As a result, the combination of P(Cl)(F  = 0.5) with IDIC increases its power conversion efficiency (PCE) to 12.1%, compared with that of P(Cl):ITIC‐Th and P(F‐Cl):IT‐4F. However, during the shelf life stability of optimized devices without encapsulation, a rapid decrease in the efficiency of P(Cl)(F  = 0.5):IDIC and P(F‐Cl):IT‐4F is observed; the PCEs of P(Cl) (F  = 0.5):IDIC and P(F‐Cl):IT‐4F decrease to 24.1% and 43.5% of their initial values for up to 350 and 398 h, respectively. On the contrary, P(Cl):ITIC‐Th exhibits superior longterm air stability with a PCE decrease of −2% (for 317‐h) and 9% (for 2002‐h) compared with the initial PCE. To understand this phenomenon, the correlation between crystallinity and miscibility of blend films is systematically investigated. In short, the balanced crystallinity and miscibility of donor and acceptor induces a relatively more stable morphology.

Cs₂AgBiBr₆ perovskite is combined with a photoactive zinc chlorophyll derivative (Zn‐Chl) as a hole‐transporting layer that is capable of sensitizing the perovskite absorber. Devices based on Zn‐Chl exhibit a 27% higher J _sc than devices based on spiro‐OMeTAD and a record power conversion efficiency of 2.79%.

The lead‐free double perovskite, Cs₂AgBiBr₆, has received keen attention as photovoltaic absorber with nontoxicity and highly stabilities. However, the large bandgap (2.1 eV) and low optical absorption property of Cs₂AgBiBr₆ have limited its power conversion efficiency (PCE) in perovskite solar cells (PSCs) to low values around 2% due to the lack in short‐circuit current density (J _sc). Herein, Cs₂AgBiBr₆ perovskite is combined with a photoactive zinc chlorophyll derivative (Zn‐Chl) as a hole‐transporting layer (HTL) that is capable of sensitizing the perovskite absorber. The Zn‐Chl‐sensitized Cs₂AgBiBr₆ device exhibits a PCE up to 2.79%, the highest value for double perovskite‐based solar cells to date, with a J _sc of 3.83 mA cm⁻², which is 22–27% higher than that of the devices with conventional nonphotoactive HTLs such as 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD), poly(3‐hexylthiophene) (P3HT), and poly(triarylamine) (PTAA). Through photophysical investigation, it is found that the Zn‐Chl not only plays the role of an HTL but also the role of a photoactive layer in the PSC devices. Moreover, the Zn‐Chl‐based device shows a much higher extinction coefficient than those based on Spiro‐OMeTAD, P3HT, and PTAA. This work demonstrates promise toward the realization and application of environmentally friendly solar cells.

In article number https://doi.org/10.1002/aenm.2019040501904050, Chaochao Qin, Alex K.‐Y. Jen, Kai Yao and co‐workers describe a generic guideline for fine tuning colloidal properties of 2D perovskites via coordination engineering of the single‐crystal precursor solution. In nonpolar co‐solvent media, the derived colloidal templates prefer to grow along the vertical direction with a narrow phase variation, elucidating the critical role of colloidal chemistry in low‐dimensional perovskite solar cells.

The amorphous–crystalline heterophase SnO₂ electron transport bilayer (Bi‐SnO₂) exhibits improved surface morphology, fewer oxygen defects, and better energy band alignment with the perovskite, which enables more efficient electron extraction. The use of Bi‐SnO₂ boosts the efficiency of small‐area (0.09 cm²) and large‐area (3.55 cm²) perovskite solar cells up to 20.39% and 14.93%, respectively.

Abstract

Improving the ohmic contact and interfacial morphology between an electron transport layer (ETL) and perovskite film is the key to boost the efficiency of planar perovskite solar cells (PSCs). In the current work, an amorphous–crystalline heterophase tin oxide bilayer (Bi‐SnO₂) ETL is prepared via a low‐temperature solution process. Compared with the amorphous SnO₂ sol–gel film (SG‐SnO₂) or the crystalline SnO₂ nanoparticle (NP‐SnO₂) counterparts, the heterophase Bi‐SnO₂ ETL exhibits improved surface morphology, considerably fewer oxygen defects, and better energy band alignment with the perovskite without sacrificing the optical transmittance. The best PSC device (active area ≈ 0.09 cm²) based on a Bi‐SnO₂ ETL is hysteresis‐less and achieves an outstanding power conversion efficiency of ≈20.39%, which is one of the highest efficiencies reported for SnO₂‐triple cation perovskite system based on green antisolvent. More fascinatingly, large‐area PSCs (active areas of ≈3.55 cm²) based on the Bi‐SnO₂ ETL also achieves an extraordinarily high efficiency of ≈14.93% with negligible hysteresis. The improved device performance of the Bi‐SnO₂‐based PSC arises predominantly from the improved ohmic contact and suppressed bimolecular recombination at the ETL/perovskite interface. The tailored morphology and energy band structure of the Bi‐SnO₂ has enabled the scalable fabrication of highly efficient, hysteresis‐less PSCs.

Three asymmetric small‐molecule acceptors are developed by changing the fluorine atoms on the terminal group of Y6 to chlorine atoms, namely SY1, SY2, and SY3, with Y6, and Y6‐4Cl are utilized as the reference. Organic solar cells based on the PM6:SY1 blend demonstrate a champion power conversion efficiency of 16.83%. This work can provide a deeper and more comprehensive understanding of applying the asymmetric molecule design method.

Abstract

Small‐molecule acceptors (SMAs)‐based organic solar cells (OSCs) have exhibited great potential for achieving high power conversion efficiencies (PCEs). Meanwhile, developing asymmetric SMAs to improve photovoltaic performance by modulating energy level distribution and morphology has drawn lots of attention. In this work, based on the high‐performance SMA (Y6), three asymmetric SMAs are developed by substituting the fluorine atoms on the terminal group with chlorine atoms, namely SY1 (two F atoms and one Cl atom), SY2 (two F atoms and two Cl atoms), and SY3 (three Cl atoms). Y6 (four F atoms) and Y6‐4Cl (four Cl atoms) are synthesized as control molecules. As a result, SY1 exhibits the shallowest lowest unoccupied molecular orbital energy level and the best molecular packing among these five acceptors. Consequently, OSCs based on PM6:SY1 yield a champion PCE of 16.83% with an open‐circuit voltage (V _OC) of 0.871 V, and a fill factor (FF) of 0.760, which is the best result among the five devices. The highest FF for the PM6:SY1‐based device is mainly ascribed to the most balanced charge transport and optimal morphology. This contribution provides deeper understanding of applying asymmetric molecule design method to further promote PCEs of OSCs.

Deuterium oxide as a solvent additive enhances the power conversion efficiency of triple‐cation perovskite solar cells. It passivates the defects, thus enhancing the charge carrier lifetimes and diffusion lengths. Partial formamidinium deuteration also helps to stabilize the PbI₆ structure. This facile approach based on selective isotope exchange could possibly be extended to other perovskite devices to improve their optoelectronic properties.

Abstract

Heavy water or deuterium oxide (D₂O) comprises deuterium, a hydrogen isotope twice the mass of hydrogen. Contrary to the disadvantages of deuterated perovskites, such as shorter recombination lifetimes and lower/invariant efficiencies, the serendipitous effect of D₂O as a beneficial solvent additive for enhancing the power conversion efficiency (PCE) of triple‐A cation (cesium (Cs)/methylammonium (MA)/formaminidium (FA)) perovskite solar cells from ≈19.2% (reference) to 20.8% (using 1 vol% D₂O) with higher stability is reported. Ultrafast optical spectroscopy confirms passivation of trap states, increased carrier recombination lifetimes, and enhanced charge carrier diffusion lengths in the deuterated samples. Fourier transform infrared spectroscopy and solid‐state NMR spectroscopy validate the N–H₂ group as the preferential isotope exchange site. Furthermore, the NMR results reveal the induced alteration of the FA to MA ratio due to deuteration causes a widespread alteration to several dynamic processes that influence the photophysical properties. First‐principles density functional theory calculations reveal a decrease in PbI₆ phonon frequencies in the deuterated perovskite lattice. This stabilizes the PbI₆ structures and weakens the electron–LO phonon (Fröhlich) coupling, yielding higher electron mobility. Importantly, these findings demonstrate that selective isotope exchange potentially opens new opportunities for tuning perovskite optoelectronic properties.

Sufficient and stable surface passivation of perovskite solar cells is realized using a novel tribenzylphosphine oxide molecule, with high cell efficiency of >22% and excellent operation stability being obtained. These achievements benefit from the strong molecule–perovskite Coulomb interaction and the formation of superstructure self‐assembly on the perovskite surface, enabled by intermolecular π–π conjugation.

Abstract

Surface passivation is an effective approach to eliminate defects and thus to achieve efficient perovskite solar cells, while the stability of the passivation effect is a new concern for device stability engineering. Herein, tribenzylphosphine oxide (TBPO) is introduced to stably passivate the perovskite surface. A high efficiency exceeding 22%, with steady‐state efficiency of 21.6%, is achieved, which is among the highest performances for TiO₂ planar cells, and the hysteresis is significantly suppressed. Further density functional theory (DFT) calculation reveals that the surface molecule superstructure induced by TBPO intermolecular π–π conjugation, such as the periodic interconnected structure, results in a high stability of TBPO–perovskite coordination and passivation. The passivated cell exhibits significantly improved stability, with sustaining 92% of initial efficiency after 250 h maximum‐power‐point tracking. Therefore, the construction of a stabilized surface passivation in this work represents great progress in the stability engineering of perovskite solar cells.

The interfaces determine the overall device performance and stability. These interfaces include the intralayer grain boundaries inside the perovskites, the interface between perovskites with electron/hole transport layer (ETL/HTL), and the interface of ETL/HTL with electrodes. With the aim of minimizing traps, promoting carrier extraction, and improving stability, herein, an overview of recent interfacial engineering strategies is provided.

Abstract

Rapid progress in the domain of perovskite solar cells (PSCs) has boosted the power conversion efficiency (PCE) of such cells to 25.2%. However, the long‐term stability of a high‐performance PSCs is still the foremost concern that hinders its practical application. The interfaces are considered as the key part that determines the overall device performance and longevity. These interfaces include the intralayer grain boundaries (GBs) inside the perovskites, the interface between perovskites with electron/hole transport layer (ETL/HTL), and the interface of ETL/HTL with top/down contacts. To acquire a deep and detailed understanding of the impacts of interfacial properties, herein, a concise overview of recent interfacial engineering strategies with the aim of minimizing traps, promoting carrier extraction, and improving stability are summarized.

Publication date: July 2020

Source: Nano Energy, Volume 73

Author(s): Guang-Xing Liang, Yan-Di Luo, Shuo Chen, Rong Tang, Zhuang-Hao Zheng, Xue-Jin Li, Xin-Sheng Liu, Yi-Ke Liu, Ying-Fen Li, Xing-Ye Chen, Zheng-Hua Su, Xiang-Hua Zhang, Hong-Li Ma, Ping Fan

Publication date: 20 May 2020

Source: Joule, Volume 4, Issue 5

Author(s): Yan Jiang, Shih-Chi Yang, Quentin Jeangros, Stefano Pisoni, Thierry Moser, Stephan Buecheler, Ayodhya N. Tiwari, Fan Fu

Chemical intuition tells us that pressure increases ordering in most known materials. The discovery of pressure‐induced disorder in the double perovskites Y₂CoIrO₆ and Y₂CoRuO₆, which is reported by Z. Deng, C.‐J. Kang, C. Jin, M. Greenblatt, and co‐workers in their Research Article on https://doi.org/10.1002/anie.202001922page 8240, is in contrast to traditional theories of order–disorder mechanisms and calls for reconsideration of pressure effects in solid state sciences.

What a boost : Undoped and Sb‐doped lead‐free 0D perovskites A₂InCl₅(H₂O) (A=Rb, Cs) have been synthesized. Doping Sb³⁺ into Rb₂InCl₅(H₂O) achieves a boost of PLQY from <2 % to 90 %. Sb‐doped A₃InCl₆ (A=Rb, Cs) are also synthesized and the effect of H₂O coordination was studied. 0D rubidium indium chloride perovskites show excellent stability.

Abstract

Zero‐dimensional (0D) lead‐free perovskites have unique structures and optoelectronic properties. Undoped and Sb‐doped all inorganic, lead‐free, 0D perovskite single crystals A₂InCl₅(H₂O) (A=Rb, Cs) are presented that exhibit greatly enhanced yellow emission. To study the effect of coordination H₂O, Sb‐doped A₃InCl₆ (A=Rb, Cs) are also synthesized and further studied. The photoluminescence (PL) color changes from yellow to green emission. Interestingly, the photoluminescence quantum yield (PLQY) realizes a great boost from <2 % to 85–95 % through doping Sb³⁺. We further explore the effect of Sb³⁺ dopants and the origin of bright emission by ultrafast transient absorption techniques. Furthermore, Sb‐doped 0D rubidium indium chloride perovskites show excellent stability. These findings not only provide a way to design a set of new high‐performance 0D lead‐free perovskites, but also reveal the relationship between structure and PL properties.

Recent progress in inorganic lead‐based and lead‐free CsBX₃ perovskite solar cells using various strategies is reviewed and their prospects and challenges in the future are discussed in detail.

Abstract

All‐inorganic perovskite semiconductors have recently drawn increasing attention owing to their outstanding thermal stability. Although all‐inorganic perovskite solar cells (PSCs) have achieved significant progress in recent years, they still fall behind their prototype organic–inorganic counterparts owing to severe energy losses. Therefore, there is considerable interest in further improving the performance of all‐inorganic PSCs by synergic optimization of perovskite films and device interfaces. This review article provides an overview of recent progress in inorganic PSCs in terms of lead‐based and lead‐free composition. The physical properties of all‐inorganic perovskite semiconductors as well as the hole/electron transporting materials are discussed to unveil the important role of composition engineering and interface modification. Finally, a discussion of the prospects and challenges for all‐inorganic PSCs in the near future is presented.

High quality films of lead‐free halide perovskite cesium tin iodide (CsSnI₃) are grown by pulsed laser deposition, a solvent‐free, single‐source in‐vacuum technique. The optically active black γ‐CsSnI₃ perovskite phase is stabilized through in situ application of an amorphous, transparent capping layer.

Abstract

The presence of a nonoptically active polymorph (yellow‐phase) competing with the optically active polymorph (black γ‐phase) at room temperature in cesium tin iodide (CsSnI₃) and the susceptibility of Sn to oxidation represent two of the biggest obstacles for the exploitation of CsSnI₃ in optoelectronic devices. Here room‐temperature single‐source in vacuum deposition of smooth black γ −CsSnI₃ thin films is reported. This is done by fabricating a solid target by completely solvent‐free mixing of CsI and SnI₂ powders and isostatic pressing. By controlled laser ablation of the solid target on an arbitrary substrate at room temperature, the formation of CsSnI₃ thin films with optimal optical properties is demonstrated. The films present a bandgap of 1.32 eV, a sharp absorption edge, and near‐infrared photoluminescence emission. These properties and X‐ray diffraction of the thin films confirm the formation of the orthorhombic (B‐γ ) perovskite phase. The thermal stability of the phase is ensured by applying in situ an Al₂O₃ capping layer. This work demonstrates the potential of pulsed laser deposition as a volatility‐insensitive single‐source growth technique of halide perovskites and represents a critical step forward in the development and future scalability of inorganic lead‐free halide perovskites.

Herein, a novel precursor (HCOOCs and HPbX₃) for deposition of high‐quality CsPbI₂Br films, irrespective of humidity is presented. CsPbI₂Br cells prepared in an atmosphere with 30% and 91% relative humidity exhibit efficiencies of 16.1% and 15.1%, respectively, which are the highest among all inorganic CsPbX₃ (X: I, Br, or mixed halides) PSCs prepared in a medium or high humid atmosphere.

Abstract

High temperature stable inorganic CsPbX₃ (X: I, Br, or mixed halides) perovskites with their bandgap tailored by tuning the halide composition offer promising opportunities in the design of ideal top cells for high‐efficiency tandem solar cells. Unfortunately, the current high‐efficiency CsPbX₃ perovskite solar cells (PSCs) are prepared in vacuum, a moisture‐free glovebox or other low‐humidity conditions due to their poor moisture stability. Herein, a new precursor system (HCOOCs, HPbI₃, and HPbBr₃) is developed to replace the traditional precursors (CsI, PbI₂, and PbBr₂) commonly used for solar cells of this type. Both the experiments and calculations reveal that a new complex (HCOOH•Cs⁺) is generated in this precursor system. The new complex is not only stable against aging in humid air ambient at 91% relative humidity, but also effectively slows the perovskite crystallization, making it possible to eliminate the popular antisolvent used in the perovskite CsPbI₂Br film deposition. The CsPbI₂Br PSCs based on the new precursor system achieve a champion efficiency of 16.14%, the highest for inorganic PSCs prepared in ambient air conditions. Meanwhile, high air stability is demonstrated for an unencapsulated CsPbI₂Br PSC with 92% of the original efficiency remaining after more than 800 h aging in ambient air.

High‐efficiency and stable dopant‐free poly(3‐hexylthiophene) (P3HT)‐based CsPbI₂Br solar cells are achieved by introducing an optimized preannealing process to engineer the nucleation and crystallization of CsPbI₂Br films. Further incorporation of an ultrathin wide‐bandgap diphenylamine derivative layer (poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co ‐(4,4′‐(N ‐(4‐sec‐butylphenyl)diphenylamine)]) to regulate the band alignment of CsPbI₂Br and P3HT delivers a record‐high efficiency of 15.50% for dopant‐free P3HT‐based CsPbI₂Br solar cells.

Abstract

CsPbI₂Br is emerging as a promising all‐inorganic material for perovskite solar cells (PSCs) due to its more stable lattice structure and moisture resistance compared to CsPbI₃, although its device performance is still much behind this counterpart. Herein, a preannealing process is developed and systematically investigated to achieve high‐quality CsPbI₂Br films by regulating the nucleation and crystallization of perovskite. The preannealing temperature and time are specifically optimized for a dopant‐free poly(3‐hexylthiophene) (P3HT)‐based device to target dopant‐induced drastic performance degradation for spiro‐OMeTAD‐based devices. The resulting P3HT‐based device exhibits comparable power conversion efficiency (PCE) to spiro‐OMeTAD‐based devices but much enhanced ambient stability with over 95% PCE after 1300 h. A diphenylamine derivative is introduced as a buffer layer to improve the energy‐level mismatch between CsPbI₂Br and P3HT. A record‐high PCE of 15.50% for dopant‐free P3HT‐based CsPbI₂Br PSCs is achieved by alleviating the open‐circuit voltage loss with the buffer layer. These results demonstrate that the preannealing processing together with a suitable buffer layer are applicable strategies for developing dopant‐free P3HT PSCs with high efficiency and stability.