liuxinye

Mesoporous boron‐doped TiO₂ (B‐TiO₂) is demonstrated as an improved electron transport layer (ETL) for perovskite solar cells for the reduction of hysteresis. The incorporation of boron dopant in TiO₂ ETL not only reduces the hysteresis but also improves device performance. Consequently, a methylammonium lead iodide photovoltaic device based on B‐TiO₂ ETL achieves a promising efficiency of 20.51% with negligible hysteresis.

Abstract

Perovskite solar cells (PSCs) have witnessed astonishing improvement in power conversion efficiency (PCE), more recently, with advances in long‐term stability and scalable fabrication. However, the presence of an anomalous hysteresis behavior in the current density–voltage characteristic of these devices remains a key obstacle on the road to commercialization. Herein, sol–gel‐processed mesoporous boron‐doped TiO₂ (B‐TiO₂) is demonstrated as an improved electron transport layer (ETL) for PSCs for the reduction of hysteresis. The incorporation of boron dopant in TiO₂ ETL not only reduces the hysteresis behavior but also improves PCE of the perovskite device. The simultaneous improvements are mainly ascribed to the following two reasons. First, the substitution of under‐coordinated titanium atom by boron species effectively passivates oxygen vacancy defects in the TiO₂ ETL, leading to increased electron mobility and conductivity, thereby greatly facilitating electron transport. Second, the boron dopant upshifts the conduction band edge of TiO₂, resulting in more efficient electron extraction with suppressed charge recombination. Consequently, a methylammonium lead iodide (MAPbI₃) photovoltaic device based on B‐TiO₂ ETL achieves a higher efficiency of 20.51% than the 19.06% of the pure TiO₂ ETL based device, and the hysteresis is reduced from 0.13% to 0.01% with the B‐TiO₂ based device showing negligible hysteresis behavior.

In this work, a “perovskite” template‐assisted structure is developed to fabricate high‐quality α‐FAPbI₃. The δ‐FAPbI₃ phases are avoided. Defects are substantially reduced with an excellent light harvesting. A power conversion efficiency of 21.24% (the highest efficiency reported for pure α‐FAPbI₃) is achieved. It also realizes a great stability in 800 h thermal ageing and 500 h light soaking.

Abstract

Formamidinium (FA) lead halide (α‐FAPbI₃) perovskites are promising materials for photovoltaic applications because of their excellent light harvesting capability (absorption edge 840 nm) and long carrier diffusion length. However, it is extremely difficult to prepare a pure α‐FAPbI₃ phase because of its easy transformation into a nondesirable δ‐FAPbI₃ phase. In the present study, a “perovskite” template (MAPbI₃‐FAI‐PbI₂‐DMSO) structure is used to avoid and suppress the formation of δ‐FAPbI₃ phases. The perovskite structure is formed via postdeposition involving the treatment of colloidal MAI‐PbI₂‐DMSO film with FAI before annealing. In situ X‐ray diffraction in vacuum shows no detectable δ‐FAPbI₃ phase during the whole synthesis process when the sample is annealed from 100 to 180 °C. This method is found to reduce defects at grain boundaries and enhance the film quality as determined by means of photoluminescence mapping and Kelvin probe force microscopy. The perovskite solar cells (PSCs) fabricated by this method demonstrate a much‐enhanced short‐circuit current density (  J _sc) of 24.99 mA cm⁻² and a power conversion efficiency (PCE) of 21.24%, which is the highest efficiency reported for pure FAPbI₃, with great stability under 800 h of thermal ageing and 500 h of light soaking in nitrogen.

A low bandgap nonfullerene acceptor (NFA) is incorporated into fullerene electron‐transporting layer (ETL) of an inverted perovskite solar cell aiming to intercept the NIR light passing through the device. However, it cannot enhance the device's NIR photoresponse. Further adding a p‐type polymer effectively enhances the device's NIR photoresponse due to better cascade energy‐level alignment and increased hole mobility.

Abstract

How to extend the photoresponse of perovskite solar cells (PVSCs) to the region of near‐infrared (NIR)/infrared light has become an appealing research subject in this field since it can better harness the solar irradiation. Herein, the typical fullerene electron‐transporting layer (ETL) of an inverted PVSC is systematically engineered to enhance device's NIR photoresponse. A low bandgap nonfullerene acceptor (NFA) is incorporated into the fullerene ETL aiming to intercept the NIR light passing through the device. However, despite forming type II charge transfer with fullerene, the blended NFA cannot enhance the device's NIR photoresponse, as limited by the poor dissociation of photoexciton induced by NIR light. Fortunately, it can be addressed by adding a p‐type polymer. The ternary bulk‐heterojunction (BHJ) ETL is demonstrated to effectively enhance the device's NIR photoresponse due to the better cascade‐energy‐level alignment and increased hole mobility. By further optimizing the morphology of such a BHJ ETL, the derived PVSC is finally demonstrated to possess a 40% external quantum efficiency at 800 nm with photoresponse extended to the NIR region (to 950 nm), contributing ≈9% of the overall photocurrent. This study unveils an effective and simple approach for enhancing the NIR photoresponse of inverted PVSCs.

The ferroelectric P(VDF‐TrFE) polymer dopant results in promoting the built‐in electric field in the absorber perovskite layer, which leads to both increasing the minority carrier diffusion length and reducing the nonradiative recombination loss. Compared to typical CH₃NH₃PbI₃‐based perovskite solar cells (PSCs), optimized FE‐PSCs present higher V _OCs up to 1.17 V and power conversion efficiency up to 18%.

Abstract

A novel ferroelectric coupling photovoltaic effect is reported to enhance the open‐circuit voltage (V _OC) and the efficiency of CH₃NH₃PbI₃ perovskite solar cells. A theoretical analysis demonstrates that this ferroelectric coupling effect can effectively promote charge extraction as well as suppress combination loss for an increased minority carrier lifetime. In this study, a ferroelectric polymer P(VDF‐TrFE) is introduced to the absorber layer in solar cells with a proper cocrystalline process. Piezoresponse force microscopy (PFM) is used to confirm that the P(VDF‐TrFE):CH₃NH₃PbI₃ mixed thin films possess ferroelectricity, while the pure CH₃NH₃PbI₃ films have no obvious PFM response. Additionally, with the applied external bias voltages on the ferroelectric films, the devices begin to show tunable photovoltaic performance, as expected for the polarization in the poling process. Furthermore, it is shown that through the ferroelectric coupled effect, the efficiency of the CH₃NH₃PbI₃‐based perovskite photovoltaic devices is enhanced by about 30%, from 13.4% to 17.3%. And the open‐circuit voltages (V _OC) reach 1.17 from 1.08 V, which is reported to be among the highest V _OCs for CH₃NH₃PbI₃‐based devices. It should be noted in particular that the thickness of the layer is less than 160 nm, which can be regarded as semi‐transparent.

The smallest fragment of dysprosium oxide is stabilized inside a fullerene. Three isomers of oxide clusterfullerenes Dy₂O@C₈₂ are synthesized and characterized by single‐crystal X‐ray diffraction. The compact size of the Dy₂O cluster leads to unusually short DyO bonds, strong magnetic anisotropy, and enhanced antiferromagnetic interactions between Dy ions. Dy₂O@C₈₂ isomers behave as single molecule magnets with broad magnetic hysteresis.

Abstract

A new class of single‐molecule magnets (SMMs) based on Dy‐oxide clusterfullerenes is synthesized. Three isomers of Dy₂O@C₈₂ with C _s(6), C _3v(8), and C _2v(9) cage symmetries are characterized by single‐crystal X‐ray diffraction, which shows that the endohedral Dy−(µ₂‐O)−Dy cluster has bent shape with very short Dy−O bonds. Dy₂O@C₈₂ isomers show SMM behavior with broad magnetic hysteresis, but the temperature and magnetization relaxation depend strongly on the fullerene cage. The short Dy−O distances and the large negative charge of the oxide ion in Dy₂O@C₈₂ result in the very strong magnetic anisotropy of Dy ions. Their magnetic moments are aligned along the Dy−O bonds and are antiferromagnetically (AFM) coupled. At low temperatures, relaxation of magnetization in Dy₂O@C₈₂ proceeds via the ferromagnetically (FM)‐coupled excited state, giving Arrhenius behavior with the effective barriers equal to the AFM‐FM energy difference. The AFM‐FM energy differences of 5.4–12.9 cm⁻¹ in Dy₂O@C₈₂ are considerably larger than in SMMs with {Dy₂O₂} bridges, and the Dy∙∙∙Dy exchange coupling in Dy₂O@C₈₂ is the strongest among all dinuclear Dy SMMs with diamagnetic bridges. Dy‐oxide clusterfullerenes provide a playground for the further tuning of molecular magnetism via variation of the size and shape of the fullerene cage.

The smallest fragment of dysprosium oxide is stabilized inside a fullerene. Three isomers of oxide clusterfullerenes Dy₂O@C₈₂ are synthesized and characterized by single‐crystal X‐ray diffraction. The compact size of the Dy₂O cluster leads to unusually short DyO bonds, strong magnetic anisotropy, and enhanced antiferromagnetic interactions between Dy ions. Dy₂O@C₈₂ isomers behave as single molecule magnets with broad magnetic hysteresis.

Abstract

A new class of single‐molecule magnets (SMMs) based on Dy‐oxide clusterfullerenes is synthesized. Three isomers of Dy₂O@C₈₂ with C _s(6), C _3v(8), and C _2v(9) cage symmetries are characterized by single‐crystal X‐ray diffraction, which shows that the endohedral Dy−(µ₂‐O)−Dy cluster has bent shape with very short Dy−O bonds. Dy₂O@C₈₂ isomers show SMM behavior with broad magnetic hysteresis, but the temperature and magnetization relaxation depend strongly on the fullerene cage. The short Dy−O distances and the large negative charge of the oxide ion in Dy₂O@C₈₂ result in the very strong magnetic anisotropy of Dy ions. Their magnetic moments are aligned along the Dy−O bonds and are antiferromagnetically (AFM) coupled. At low temperatures, relaxation of magnetization in Dy₂O@C₈₂ proceeds via the ferromagnetically (FM)‐coupled excited state, giving Arrhenius behavior with the effective barriers equal to the AFM‐FM energy difference. The AFM‐FM energy differences of 5.4–12.9 cm⁻¹ in Dy₂O@C₈₂ are considerably larger than in SMMs with {Dy₂O₂} bridges, and the Dy∙∙∙Dy exchange coupling in Dy₂O@C₈₂ is the strongest among all dinuclear Dy SMMs with diamagnetic bridges. Dy‐oxide clusterfullerenes provide a playground for the further tuning of molecular magnetism via variation of the size and shape of the fullerene cage.

A N,1‐diiodoformamidine (DIFA) additive is introduced in the perovskite precursor to attain high efficiency and stable perovskite solar cells (PSCs). Upon the addition of 2% DIFA, the compact, smooth, relatively hydrophobic, and large grained perovskite films are achieved with highly efficient defect passivation, which substantially increases the power conversion efficiency from 19.07% for the control device to 21.22%.

Abstract

A high‐quality perovskite photoactive layer plays a crucial role in determining the device performance. An additive engineering strategy is introduced by utilizing different concentrations of N,1‐diiodoformamidine (DIFA) in the perovskite precursor solution to essentially achieve high‐quality monolayer‐like perovskite films with enhanced crystallinity, hydrophobic property, smooth surface, and grain size up to nearly 3 µm, leading to significantly reduced grain boundaries, trap densities, and thus diminished hysteresis in the resultant perovskite solar cells (PSCs). The optimized devices with 2% DIFA additive show the best device performance with a significantly enhanced power conversion efficiency (PCE) of 21.22%, as compared to the control devices with the highest PCE of 19.07%. 2% DIFA modified devices show better stability than the control ones. Overall, the introduction of DIFA additive is demonstrated to be a facile approach to obtain high‐efficiency, hysteresis‐less, and simultaneously stable PSCs.

A N,1‐diiodoformamidine (DIFA) additive is introduced in the perovskite precursor to attain high efficiency and stable perovskite solar cells (PSCs). Upon the addition of 2% DIFA, the compact, smooth, relatively hydrophobic, and large grained perovskite films are achieved with highly efficient defect passivation, which substantially increases the power conversion efficiency from 19.07% for the control device to 21.22%.

Abstract

A high‐quality perovskite photoactive layer plays a crucial role in determining the device performance. An additive engineering strategy is introduced by utilizing different concentrations of N,1‐diiodoformamidine (DIFA) in the perovskite precursor solution to essentially achieve high‐quality monolayer‐like perovskite films with enhanced crystallinity, hydrophobic property, smooth surface, and grain size up to nearly 3 µm, leading to significantly reduced grain boundaries, trap densities, and thus diminished hysteresis in the resultant perovskite solar cells (PSCs). The optimized devices with 2% DIFA additive show the best device performance with a significantly enhanced power conversion efficiency (PCE) of 21.22%, as compared to the control devices with the highest PCE of 19.07%. 2% DIFA modified devices show better stability than the control ones. Overall, the introduction of DIFA additive is demonstrated to be a facile approach to obtain high‐efficiency, hysteresis‐less, and simultaneously stable PSCs.

The ferroelectric P(VDF‐TrFE) polymer dopant results in promoting the built‐in electric field in the absorber perovskite layer, which leads to both increasing the minority carrier diffusion length and reducing the nonradiative recombination loss. Compared to typical CH₃NH₃PbI₃‐based perovskite solar cells (PSCs), optimized FE‐PSCs present higher V _OCs up to 1.17 V and power conversion efficiency up to 18%.

Abstract

A novel ferroelectric coupling photovoltaic effect is reported to enhance the open‐circuit voltage (V _OC) and the efficiency of CH₃NH₃PbI₃ perovskite solar cells. A theoretical analysis demonstrates that this ferroelectric coupling effect can effectively promote charge extraction as well as suppress combination loss for an increased minority carrier lifetime. In this study, a ferroelectric polymer P(VDF‐TrFE) is introduced to the absorber layer in solar cells with a proper cocrystalline process. Piezoresponse force microscopy (PFM) is used to confirm that the P(VDF‐TrFE):CH₃NH₃PbI₃ mixed thin films possess ferroelectricity, while the pure CH₃NH₃PbI₃ films have no obvious PFM response. Additionally, with the applied external bias voltages on the ferroelectric films, the devices begin to show tunable photovoltaic performance, as expected for the polarization in the poling process. Furthermore, it is shown that through the ferroelectric coupled effect, the efficiency of the CH₃NH₃PbI₃‐based perovskite photovoltaic devices is enhanced by about 30%, from 13.4% to 17.3%. And the open‐circuit voltages (V _OC) reach 1.17 from 1.08 V, which is reported to be among the highest V _OCs for CH₃NH₃PbI₃‐based devices. It should be noted in particular that the thickness of the layer is less than 160 nm, which can be regarded as semi‐transparent.

Publication date: 18 September 2019

Source: Joule, Volume 3, Issue 9

Author(s): Xiaotian Hu, Xiangchuan Meng, Lin Zhang, Yanyan Zhang, Zheren Cai, Zengqi Huang, Meng Su, Yang Wang, Mingzhu Li, Fengyu Li, Xi Yao, Fuyi Wang, Wei Ma, Yiwang Chen, Yanlin Song

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Nature Energy, Published online: 17 June 2019; doi:10.1038/s41560-019-0406-2

Nature Energy, Published online: 17 June 2019; doi:10.1038/s41560-019-0400-8

Publication date: 21 August 2019

Source: Joule, Volume 3, Issue 8

Author(s): Jaehoon Chung, Seong Sik Shin, Geunjin Kim, Nam Joong Jeon, Tae-Youl Yang, Jun Hong Noh, Jangwon Seo

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Publication date: 18 September 2019

Source: Joule, Volume 3, Issue 9

Author(s): Minjin Kim, Gi-Hwan Kim, Tae Kyung Lee, In Woo Choi, Hye Won Choi, Yimhyun Jo, Yung Jin Yoon, Jae Won Kim, Jiyun Lee, Daihong Huh, Heon Lee, Sang Kyu Kwak, Jin Young Kim, Dong Suk Kim

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Publication date: 17 July 2019

Source: Joule, Volume 3, Issue 7

Author(s): Dong Hoe Kim, Christopher P. Muzzillo, Jinhui Tong, Axel F. Palmstrom, Bryon W. Larson, Chungseok Choi, Steven P. Harvey, Stephen Glynn, James B. Whitaker, Fei Zhang, Zhen Li, Haipeng Lu, Maikel F.A.M. van Hest, Joseph J. Berry, Lorelle M. Mansfield, Yu Huang, Yanfa Yan, Kai Zhu

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Publication date: 21 August 2019

Source: Joule, Volume 3, Issue 8

Author(s): Xiaopeng Zheng, Joel Troughton, Nicola Gasparini, Yuanbao Lin, Mingyang Wei, Yi Hou, Jiakai Liu, Kepeng Song, Zhaolai Chen, Chen Yang, Bekir Turedi, Abdullah Y. Alsalloum, Jun Pan, Jie Chen, Ayan A. Zhumekenov, Thomas D. Anthopoulos, Yu Han, Derya Baran, Omar F. Mohammed, Edward H. Sargent

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All-perovskite–based polycrystalline thin-film tandem solar cells have the potential to deliver efficiencies of >30%. However, the performance of all-perovskite–based tandem devices has been limited by the lack of high-efficiency, low–band gap tin-lead (Sn-Pb) mixed-perovskite solar cells (PSCs). We found that the addition of guanidinium thiocyanate (GuaSCN) resulted in marked improvements in the structural and optoelectronic properties of Sn-Pb mixed, low–band gap (~1.25 electron volt) perovskite films. The films have defect densities that are lower by a factor of 10, leading to carrier lifetimes of greater than 1 microsecond and diffusion lengths of 2.5 micrometers. These improved properties enable our demonstration of >20% efficient low–band gap PSCs. When combined with wider–band gap PSCs, we achieve 25% efficient four-terminal and 23.1% efficient two-terminal all-perovskite–based polycrystalline thin-film tandem solar cells.

Publication date: 19 June 2019

Source: Joule, Volume 3, Issue 6

Author(s): Rui Wang, Jingjing Xue, Lei Meng, Jin-Wook Lee, Zipeng Zhao, Pengyu Sun, Le Cai, Tianyi Huang, Zhengxu Wang, Zhao-Kui Wang, Yu Duan, Jonathan Lee Yang, Shaun Tan, Yonghai Yuan, Yu Huang, Yang Yang

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