ZHANG JIAJIA

In article number https://doi.org/10.1002/aenm.2020011492001149, Hyojung Cha, James R. Durrant and co‐workers investigate the morphology and exciton/charge carrier dynamics in bulk heterojunctions of the donor polymer PTQ10 and molecular acceptor IDIC. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in organic solar cells, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices.

An amphiphilic dendritic block copolymer is developed to serve as an efficient surface modifier of ZnO electron‐transporting layer in an organic photovoltaic device. When using an interlayer based on its hybridization with gold nanoparticles, the device can deliver improved performance and possess a lifetime of over 1.79 years when stored at room temperature in inert conditions.

Abstract

Herein, interfacial engineering is demonstrated to improve the thermal stability of non‐fullerene bulk‐heterojunction (BHJ) OPVs to a practical level. An amphiphilic dendritic block copolymer (DBC) is developed through a facile coupling method and employed as the surface modifier of ZnO electron‐transporting layer in inverted OPVs. Besides showing distinct self‐assembly behavior, the synthesized DBC possesses high compatibility with plasmonic gold nanoparticles (NPs) due to the constituent malonamide and ethylene oxide units. The hybrid DBC@AuNPs interlayer is shown to improve device's performance from 14.0% to 15.4% because it enables better energy‐level alignment and improves interfacial compatibility at the ZnO/BHJ interface. Moreover, the DBC@AuNPs interlayer not only improves the interfacial thermal stability at the ZnO/BHJ interface but also endows a more ideal BHJ morphology with an enhanced thermal robustness. The derived device reserves 77% of initial PCE after thermal aging at 65 °C for 3000 h and yields an extended T ₈₀ lifetime of >1100 h when stored at a constant thermal condition at 65 °C, outperforming the control device. Finally, the device is evaluated to possess a T ₈₀ lifetime of over 1.79 years at room temperature (298 K) when stored in an inert condition, showing great potential for commercialization.

Publication date: 18 November 2020

Source: Joule, Volume 4, Issue 11

Author(s): Kuan Liu, Qiong Liang, Minchao Qin, Dong Shen, Hang Yin, Zhiwei Ren, Yaokang Zhang, Hengkai Zhang, Patrick W.K. Fong, Zehan Wu, Jiaming Huang, Jianhua Hao, Zijian Zheng, Shu Kong So, Chun-Sing Lee, Xinhui Lu, Gang Li

Publication date: 16 December 2020

Source: Joule, Volume 4, Issue 12

Author(s): Anyi Mei, Yusong Sheng, Yue Ming, Yue Hu, Yaoguang Rong, Weihua Zhang, Shulin Luo, Guangren Na, Chengbo Tian, Xiaomeng Hou, Yuli Xiong, Zhihui Zhang, Shuang Liu, Satoshi Uchida, Tae-Woong Kim, Yongbo Yuan, Lijun Zhang, Yinhua Zhou, Hongwei Han

Herein the morphology and exciton/charge carrier dynamics in bulk heterojunctions of the donor polymer PTQ10 and molecular acceptor IDIC are investigated. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in organic solar cells, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices.

Abstract

Herein the morphology and exciton/charge carrier dynamics in bulk heterojunctions (BHJs) of the donor polymer PTQ10 and molecular acceptor IDIC are investigated. PTQ10:IDIC BHJs are shown to be particularly promising for low cost organic solar cells (OSCs). It is found that both PTQ10 and IDIC show remarkably high crystallinity in optimized BHJs, with GIWAXS data indicating pi‐pi stacking coherence lengths of up to 8 nm. Exciton‐exciton annihilation studies indicate long exciton diffusion lengths for both neat materials (19 nm for PTQ10 and 9.5 nm for IDIC), enabling efficient exciton separation with half lives of 1 and 3 ps, despite the high degree of phase segregation in this blend. Transient absorption data indicate exciton separation leads to the formation of two spectrally distinct species, assigned to interfacial charge transfer (CT) states and separated charges. CT state decay is correlated with the appearance of additional separate charges, indicating relatively efficient CT state dissociation, attributed to the high crystallinity of this blend. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in OSCs, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices.

Applied Physics Letters, Volume 117, Issue 12, September 2020.
In donor–acceptor (D–A) heterojunction organic solar cells, hot and cold charge transfer (CT) states are formed at the interface as the precursor for subsequent charge separations. Hot CT states dissociate easily because they are loosely bound, while for cold CT states, the origin of their high-efficiency charge separations still remains heavily debated. Here, we propose a simple but effective methodology that can be used to simulate the cold CT dissociation process and, thereby, the multiple factors which may essentially affect the charge separation efficiency and can be conveniently investigated. The energy barriers on the path from cold CT to the separated charges are analyzed by calculating the adiabatic potential energy surfaces of the lowest-energy excitonic state. The calculation results indicate that the D–A molecular coupling strength and coupling area, D–A energetic offset, charge carrier delocalizations, interfacial Coulomb screening strength, and interfacial disorders can essentially affect the charge separation efficiency of a cold CT state.

Annealing‐free solution‐processable aqueous MoO _x are developed and applied in bulk‐heterojunction polymer solar cells based on non‐fullerene system PBDB‐T‐2F:Y6. The solar cells with aqueous MoO _x exhibit higher efficiencies and better stabilities without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

Abstract

A charge transport layer based on transition metal‐oxides prepared by an anhydrous sol–gel method normally requires high‐temperature annealing to achieve the desired quality. Although annealing is not a difficult process in the laboratory, it is definitely not a simple process in mass production, such as roll‐to‐roll, because of the inevitable long cooling step that follows. Therefore, the development of an annealing‐free solution‐processable metal‐oxide is essential for the large‐scale commercialization. In this work, a room‐temperature processable annealing‐free “aqueous” MoO _x solution is developed and applied in non‐fullerene PBDB‐T‐2F:Y6 solar cells. By adjusting the concentration of water in the sol–gel route, an annealing‐free MoO _x with excellent electrical properties is successfully developed. The PBDB‐T‐2F:Y6 solar cell with the general MoO _x prepared by the anhydrous sol–gel method shows a low efficiency of 7.7% without annealing. If this anhydrous MoO _x is annealed at 200 °C, the efficiency is recovered to 17.1%, which is a normal value typically observed in conventional structure PBDB‐T‐2F:Y6 solar cells. However, without any annealing process, the solar cell with aqueous MoO _x exhibits comparable performance of 17.0%. In addition, the solar cell with annealing‐free aqueous MoO _x exhibits better performance and stability without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

A series of copolymers via a random copolymerization approach are designed and synthesized. The well‐defined fibril interpenetrating morphology with appropriate phase separation in PT2‐based blends can efficiently suppress the unfavorable aggregation, resulting in excellent morphological stability and high efficiency. The work demonstrates the importance of optimization of fibril network morphology in realizing high‐efficiency and ambient‐stable polymer solar cells.

Abstract

Morphological stability is crucially important for the long‐term stability of polymer solar cells (PSCs). Many high‐efficiency PSCs suffer from metastable morphology, resulting in severe device degradation. Here, a series of copolymers is developed by manipulating the content of chlorinated benzodithiophene‐4,8‐dione (T1‐Cl) via a random copolymerization approach. It is found that all the copolymers can self‐assemble into a fibril nanostructure in films. By altering the T1‐Cl content, the polymer crystallinity and fibril width can be effectively controlled. When blended with several nonfullerene acceptors, such as TTPTT‐4F, O‐INIC3, EH‐INIC3, and Y6, the optimized fibril interpenetrating morphology can not only favor charge transport, but also inhibit the unfavorable molecular diffusion and aggregation in active layers, leading to excellent morphological stability. The work demonstrates the importance of optimization of fibril network morphology in realizing high‐efficiency and ambient‐stable PSCs, and also provides new insights into the effect of chemical structure on the fibril network morphology and photovoltaic performance of PSCs.

An inorganic CsPbI₂Br perovskite solar cell employing organic ligands armored ZnO as the electron transport materials achieves a maximum power conversion efficiency of 16.84%, with superior photo‐ and thermal‐ stabilities.

Abstract

Inorganic perovskite solar cells (PSCs) have witnessed great progress in recent years due to their superior thermal stability. As a representative, CsPbI₂Br is attracting considerable attention as it can balance the high efficiency of CsPbI₃ and the stability of CsPbBr₃. However, most research employs doped charge transport materials or applies bilayer transport layers to obtain decent performance, which vastly complicates the fabrication process and scarcely satisfies the commercial production requirement. In this work, all‐layer‐doping‐free inorganic CsPbI₂Br PSCs using organic ligands armored ZnO as the electron transport materials achieve an encouraging performance of 16.84%, which is one of the highest efficiencies among published works. Meanwhile, both the ZnO‐based CsPbI₂Br film and device show superior photostability under continuous white light‐emitting diode illumination and improved thermal stability under 85 °C. The remarkable enhanced performance arises from the favorable organic ligands (acetate ions) residue in the ZnO film, which not only can conduce to maintain high crystallinity of perovskite, but also passivate traps at the interface through cesium/acetate interactions, thus suppressing the photo‐ and thermal‐ induced perovskite degradation.

Publication date: 18 November 2020

Source: Joule, Volume 4, Issue 11

Author(s): Shaun Tan, Ilhan Yavuz, Marc H. Weber, Tianyi Huang, Chung-Hao Chen, Rui Wang, Hao-Cheng Wang, Jeong Hoon Ko, Selbi Nuryyeva, Jingjing Xue, Yepin Zhao, Kung-Hwa Wei, Jin-Wook Lee, Yang Yang

Publication date: 14 October 2020

Source: Joule, Volume 4, Issue 10

Author(s): Li Nian, Yuanyuan Kan, Ke Gao, Ming Zhang, Na Li, Guanqing Zhou, Sae Byeok Jo, Xueliang Shi, Francis Lin, Qikun Rong, Feng Liu, Guofu Zhou, Alex K.-Y. Jen

Applied Physics Letters, Volume 117, Issue 8, August 2020.
Photoresponse is affected by the microscopic structure and orientation of the perovskite crystals, but it is difficult to quantify the individual grain size and always acts as homogeneous. Using scanning probe microscopy, the local electrical properties of individual grains in all-inorganic perovskites are mapped. Surface potential variations on lateral distance scales within or larger than one grain size are presented. Among perovskite grains, three discrete photoconductivity levels are identified, corresponding to the facet-dependent density of trap states, which was further demonstrated by the light intensity dependence of the local current–voltage curve of each grain.

Applied Physics Letters, Volume 117, Issue 9, August 2020.
All-inorganic perovskite solar cells advancing in phase and thermal stability are regarded as promising candidates for high-performance optoelectronic application. Herein, a photo-assisted deposited titanium dioxide was designed and utilized as the electron-transporting layer. Photo-assisted deposited titanium dioxide demonstrated a low interfacial recombination rate and high carrier extraction efficiency. Consequently, CsPbI2Br-based all inorganic perovskite solar cells exhibit power conversion efficiencies of up to a value of 13.69%. This photo-assisted deposition method is a promising approach for scalable, convenient, and inexpensive fabrication in the future.

Applied Physics Letters, Volume 117, Issue 8, August 2020.
Perovskite ABO3 as one of the most common structures has demonstrated great structural flexibility and electronic applications. Evolving from perovskite, the typical double perovskite A2BB′O6 has two element species (B/B′), where the ordered arrangements of BO6 and B′O6 octahedron provide much more tunability. Especially, by applying external pressure, the energetic order between different phases in perovskite and double perovskite materials can be notably modified with more fascinating physical properties. However, it is still a challenge to propose a general model to explain and predict the high-pressure structures and properties of various perovskites and double perovskites due to their flexibility and complexity. In this perspective, we will discuss pressure effects on the crystalline structure and electronic configurations in some perovskites and double perovskites. We then focus on a prediction method for the evolution of the lattice and electronic structure for such materials with pressure. Finally, we will give a perspective on current challenges and opportunities for controlling and optimizing structural and electronic states of a given material for optimized functionalities.

Applied Physics Letters, Volume 117, Issue 7, August 2020.
In recent years, organic halide perovskites have attracted increasing attention from scientists. To understand the device's operational mechanism, obtaining their valence band maxima (VBMs) using ultraviolet photoelectron spectroscopy plays a critical role in determining their electronic structures and related energy level alignments. Two methods are commonly used to extract their valence band (VB) edge from either linear or logarithmic intensity scales to reach the agreement with theoretical calculations. However, the consistency behind these two methods is not revealed. In this report, we have quantitatively studied VB edges for CH3NH3PbI3 and CH3NH3PbBr3 single crystals using different photon energies. After considering both their origins of orbital hybridizations and density of state (intensity) distributions at various momentum spaces, it is revealed that precise VBMs from linear scales can be realized. The VBMs obtained from M symmetry points are 1.13 eV away from the Fermi level for CH3NH3PbI3 and 1.29 eV for CH3NH3PbBr3, suggesting that the VBMs (at the R point) are 0.86 eV for CH3NH3PbI3 and 0.89 eV for CH3NH3PbBr3. Our findings explain the mechanism of precisely obtaining VBMs from these halide perovskite single crystals.

Ion migration plays critical roles in the functionalities of metal halide perovskites. Herein, using newly developed time‐resolved time‐of‐flight secondary ion mass spectrometry, hysteretic CH₃NH₃ ⁺ and I⁻ migrations in CH₃NH₃PbI₃ are observed, where CH₃NH₃ ⁺ migration hysteresis is illumination‐dependent. The ion redistribution in CH₃NH₃PbI₃ can lead to a permanent spontaneous current after the application of electric bias.

Abstract

The gap in understanding how underlying chemical dynamics impact the functionality of metal halide perovskites (MHPs) leads to the controversy about the origin of many phenomena associated with ion migration in MHPs. In particular, the debate regarding the impact of ion migration on current–voltage (I–V) hysteresis of MHPs devices has lasted for many years, where the difficulty lies in directly uncovering the chemical dynamics, as well as identifying and separating the impact of specific ions. In this work, using a newly developed time‐resolved time‐of‐flight secondary ion mass spectrometry CH₃NH₃ ⁺ and I⁻ migrations in CH₃NH₃PbI₃ are directly observed, revealing hysteretic CH₃NH₃ ⁺ and I⁻ migrations. Additionally, hysteretic CH₃NH₃ ⁺ migration is illumination‐dependent. Correlating these results with the I–V characterization, this work uncovers that CH₃NH₃ ⁺ redistribution can induce a remanent field leading to a spontaneous current in the device. It unveils that the CH₃NH₃ ⁺ migration is responsible for the illumination‐associated I–V hysteresis in MHPs. Hysteretic ion migration has not been uncovered and the contribution of any ions (e.g., CH₃NH₃ ⁺) has not been specified before. Such insightful and detailed information has up to now been missing, which is critical to improving MHPs photovoltaic performance and developing MHPs‐based memristors and synaptic devices.

2D perovskites are of great importance to increase both the efficiency and stability of perovskite interfaces. Motivated by the stronger halogen bond interaction, (5FBzAI)₂PbI₄ used as a capping layer in 3D/2D systems self‐organizes with an in‐plane crystal orientation, inducing a reproducible increase of ≈60 mV in the V _oc, and remarkable operational stability.

Abstract

Despite organic/inorganic lead halide perovskite solar cells becoming one of the most promising next‐generation photovoltaic materials, instability under heat and light soaking remains unsolved. In this work, a highly hydrophobic cation, perfluorobenzylammonium iodide (5FBzAI), is designed and a 2D perovskite with reinforced intermolecular interactions is engineered, providing improved passivation at the interface that reduces charge recombination and enhances cell stability compared with benchmark 2D systems. Motivated by the strong halogen bond interaction, (5FBzAI)₂PbI₄ used as a capping layer aligns in in‐plane crystal orientation, inducing a reproducible increase of ≈60 mV in the V _oc, a twofold improvement compared with its analogous monofluorinated phenylethylammonium iodide (PEAI) recently reported. This endows the system with high power conversion efficiency of 21.65% and extended operational stability after 1100 h of continuous illumination, outlining directions for future work.

Applied Physics Letters, Volume 117, Issue 6, August 2020.
The development of high-performance lead-free perovskite solar cells (PSCs) is important to address the environmental concern of lead perovskite. In recent years, tin perovskite solar cells (TPSCs) have been developing quickly and emerging as a promising candidate for high-efficiency lead-free PSCs. In this Perspective, we summarize recent work of our group including the use of a low-dimensional structure, film growth kinetic control, and device engineering. In the end, the challenges in TPSCs and potential strategies toward high-efficiency TPSCs are discussed.

The M13 bacteriophage functions as an effective perovskite growth template and a passivator in perovskite solar cells. This is owing to its filamentous and uniform dimension, as well as the amino acids on its surface. These effects enhance when the M13 viruses are denatured at high temperature. The efficiency increases from 17.8% to 20.1% upon addition of the denatured viruses.

Abstract

The M13 bacteriophage, a nature‐inspired environmentally friendly biomaterial, is used as a perovskite crystal growth template and a grain boundary passivator in perovskite solar cells. The amino groups and carboxyl groups of amino acids on the M13 bacteriophage surface function as Lewis bases, interacting with the perovskite materials. The M13 bacteriophage‐added perovskite films show a larger grain size and reduced trap‐sites compared with the reference perovskite films. In addition, the existence of the M13 bacteriophage induces light scattering effect, which enhances the light absorption particularly in the long‐wavelength region around 825 nm. Both the passivation effect of the M13 bacteriophage coordinating to the perovskite defect sites and the light scattering effect intensify when the M13 virus‐added perovskite precursor solution is heated at 90 °C prior to the film formation. Heating the solution denatures the M13 bacteriophage by breaking their inter‐ and intra‐molecular bondings. The denatured M13 bacteriophage‐added perovskite solar cells exhibit an efficiency of 20.1% while the reference devices give an efficiency of 17.8%. The great improvement in efficiency comes from all of the three photovoltaic parameters, namely short‐circuit current, open‐circuit voltage, and fill factor, which correspond to the perovskite grain size, trap‐site passivation, and charge transport, respectively.

Two wide bandgap conjugated polymers PBPD‐p and PBPD‐m with alkyl side chains substituted at the para‐position and meta‐position, respectively, are synthesized. Compared with PBPD‐p, the devices based on PBPD‐m exhibit a higher efficiency of 11.95% with increased open‐circuit voltage, short‐circuit current density, and fill factor, simultaneously.

Abstract

Two wide‐bandgap (WBG) conjugated polymers (PBPD‐p and PBPD‐m) based on phenyl‐substituted benzodithiophene (BDT) with the different substitution position of the alkyl side chain and benzodithiophene‐4,8‐dione (BDD) units are designed and synthesized to investigate the influence of alkyl substitution position on the photovoltaic performance of polymers in polymer solar cells (PSCs). The thermogravimetric analysis, absorption spectroscopy, molecular energy level, X‐ray diffraction, charge transport and photovoltaic performance of the polymers are systematically studied. Compared with PBPD‐p, PBPD‐m exhibits a slight blue‐shift but a deeper highest occupied molecular orbital (HOMO) energy level, a tighter alkyl chain packing and a higher hole mobility. The PBPD‐m‐based PSCs blended with acceptor IT‐4F shows a higher power conversion efficiency (PCE) of 11.95% with a high open‐circuit voltage (V _oc) of 0.88 V, a short‐circuit current density (J _sc) of 19.76 mA cm⁻² and a fill factor (FF) of 68.7% when compared with the PCE of 6.97% with a V _oc of 0.81 V, a J _sc of 15.97 mA cm⁻² and an FF of 53.9% for PBPD‐p. These results suggest that it is a feasible and effective strategy to optimize photovoltaic properties of WBG polymers by changing the substitution position of alkyl side chain in PSCs.

Publication date: 16 September 2020

Source: Joule, Volume 4, Issue 9

Author(s): Yihua Chen, Shunquan Tan, Nengxu Li, Bolong Huang, Xiuxiu Niu, Liang Li, Mingzi Sun, Yu Zhang, Xiao Zhang, Cheng Zhu, Ning Yang, Huachao Zai, Yiliang Wu, Sai Ma, Yang Bai, Qi Chen, Fei Xiao, Kangwen Sun, Huanping Zhou

Publication date: 16 September 2020

Source: Joule, Volume 4, Issue 9

Author(s): Lennart K. Reb, Michael Böhmer, Benjamin Predeschly, Sebastian Grott, Christian L. Weindl, Goran I. Ivandekic, Renjun Guo, Christoph Dreißigacker, Roman Gernhäuser, Andreas Meyer, Peter Müller-Buschbaum

Applied Physics Letters, Volume 117, Issue 4, July 2020.
Thanks to their unique combination of semiconducting properties and a large cross section for energetic photons, metal halide perovskites could theoretically achieve high x-ray to charge carriers conversion rates, making them materials of high interest for the direct x-ray detection. In this work, we focus on the transport properties of methylammonium lead tribromide (MAPbBr3) single crystals. Time of Flight measurements and x-ray focused experiments along the edge of the samples were carried out. We report homogenous holes transit throughout the thickness of the samples as well as poor electrons transit. We also report the continuity of the electric field throughout the thickness of the MAPbBr3 samples, and we present preliminary fitting results to discuss its nature.