Chen Weijie

Mitigating surface problems of perovskite thin single crystals by one multifunctional molecule leads to improvement of power conversion efficiency as well as moisture and reverse-bias stability of single-crystal perovskite solar cells. The modified devices exhibit an impressive efficiency of 22.2%, which is the highest value for single-crystal MAPbI₃ perovskite solar cells.

Abstract

Metal halide perovskite single crystals are promising for diverse optoelectronic applications due to their outstanding properties. In comparison to the bulk, the crystal surface suffers from high defect density and is moisture sensitive; however, surface modification strategies of perovskite single crystals are relatively deficient. Herein, solar cells based on methylammonium lead triiodide (MAPbI₃) thin single crystals are selected as a prototype to improve single-crystal perovskite devices by surface modification. The surface trap passivation and protection against moisture of MAPbI₃ thin single crystals are achieved by one bifunctional molecule 3-mercaptopropyl(dimethoxy)methylsilane (MDMS). The sulfur atom of MDMS can coordinate with bare Pb²⁺ of MAPbI₃ single crystals to reduce surface defect density and nonradiative recombination. As a result, the modified devices show a remarkable efficiency of 22.2%, which is the highest value for single-crystal MAPbI₃ solar cells. Moreover, MDMS modification mitigates surface ion migration, leading to enhanced reverse-bias stability. Finally, the cross-link of silane molecules forms a protective layer on the crystal surface, which results in enhanced moisture stability of both materials and devices. This work provides an effective way for surface modification of perovskite single crystals, which is important for improving the performance of single-crystal perovskite solar cells, photodetectors, X-ray detectors, etc.

Regular and random double-cable conjugated polymers with pendent Y-series acceptors are designed and synthesized, in which the random copolymer provides a high efficiency of 13.02% compared to the regular polymer with an efficiency of 2.75% in single-component organic solar cells.

Abstract

Double-cable conjugated polymers with pendent electron acceptors, including fullerene, rylene diimides, and nonfused acceptors, have been developed for application in single-component organic solar cells (SCOSCs) with efficiencies approaching 10%. In this work, Y-series electron acceptors have been firstly incorporated into double-cable polymers in order to further improve the efficiencies of SCOSCs. A highly crystalline Y-series acceptor based on quinoxaline core and the random copolymerized strategy are used to optimize the ambipolar charge transport and the nanophase separation of the double-cable polymers. As a result, an efficiency of 13.02% is obtained in the random double-cable polymer, representing the highest performance in SCOSCs, while the regular double-cable polymer only provides a low efficiency of 2.75%. The significantly enhanced efficiencies are attributed to higher charge carrier mobilities, better ordering conjugated backbones and Y-series acceptors in random double-cable polymers.

An ionic-liquid polymer additive (poly[Se-MI][BF₄]) is developed to stabilize perovskite precursor inks used to fabricate perovskite solar cells (pero-SCs). A chemical homogeneity of the inks contributes to improving the quality of perovskite films by stabilizing the colloids and compositions for over two months. Moreover, polymers anchored at the grain boundaries can further suppress the migration of I⁻ ions. Thus, the pero-SCs exhibit overall improved stability and efficiency.

Abstract

The stability-related issues arising from the perovskite precursor inks, films, device structures and interdependence remain severely under-explored to date. Herein, we designed an ionic-liquid polymer (poly[Se-MI][BF₄]), containing functional moieties like carbonyl (C=O), selenium (Se⁺), and tetrafluoroborate (BF₄ ⁻) ions, to stabilize the whole device fabrication process. The C=O and Se⁺ can coordinate with lead and iodine (I⁻) ions to stabilize lead polyhalide colloids and the compositions of the perovskite precursor inks for over two months. The Se⁺ anchored on grain boundaries and the defects passivated by BF₄ ⁻ efficiently suppress the dissociation and migration of I⁻ in perovskite films. Benefiting from the synergistic effects of poly[Se-MI][BF₄], high efficiencies of 25.10 % and 20.85 % were exhibited by a 0.062-cm² device and 15.39-cm² module, respectively. The devices retained over 90 % of their initial efficiency under operation for 2200 h.

Publication date: July 2023

Source: Journal of Energy Chemistry, Volume 82

Author(s): Yinhua Lv, Bing Cai, Ruihan Yuan, Yihui Wu, Quinn Qiao, Wen-Hua Zhang

Publication date: May 2023

Source: Nano Energy, Volume 109

Author(s): Yang Yang, Lu Liu, Jianxun Li, Shuai Zhao, Zhen Chang, Le Wang, Dongqi Yu, Kai Wang, Shengzhong (Frank) Liu

Publication date: May 2023

Source: Nano Energy, Volume 109

Author(s): Mengqi Jin, Chong Chen, Fumin Li, Zhitao Shen, Hu Shen, Dong Yang, Rong Liu, Huilin Li, Ying Liu, Chao Dong, Mingtai Wang

Herein, a cost-effective yet robust interfacial bidirectional therapy strategy is developed to simultaneously depress dopant lithium ions diffusion, suppress defects states and inhibit toxic lead (Pb) leakage of perovskite solar cells. The unencapsulated modified devices based on formamidinium-lead-triiodide (FAPbI₃) perform better than control devices when exposed to different harsh environments. And the modified device delivers a champion efficiency of 23.27% with mitigated Pb leakage. More importantly, the developed strategy is also adaptable to methylammonium-lead-triiodide (MAPbI₃)-based device for simultaneous enhancement of the device stability and efficiency (20.82%).

Abstract

Perovskite solar cells (PSCs) have witnessed rapid development toward commercialization based on their superior efficiency except for some remained misgivings about their poor stability primarily originating from interfacial problems. Robust back interface for neutralization of crystal defects, depression of dopant lithium ions (Li⁺) diffusion, and even inhibition of toxic lead (Pb) leakage is highly desirable; however, it remains a great challenge. Herein, a cost-effective interfacial therapy approach is developed to simultaneously alleviate the obstacles aforementioned. A small molecule, 1,4-dithiane with unique chair structure, is adapted to interact with under-coordinated Pb²⁺ on perovskite surface and Li⁺ from hole transport layer, neutralizing interfacial defects and suppressing Li⁺ diffusion. Besides, the presence of 1,4-dithiane can efficiently modulate interfacial energetics, enhance hydrophobicity of PSCs, and anchor Pb atoms via SPb bond. Consequently, the target devices perform better than control devices when exposed to light-soaking, moisture, and thermal stress owing to the synergistic suppression of trap-state density, ions migration, and moisture permeation. The optimized target device delivers a champion efficiency of 23.27% with mitigated Pb leakage. This study demonstrates a promising functionalized modification strategy for constructing efficient, stable, and eco-friendly PSCs.

Herein, it is demonstrated that the classical Y6-based binary device can be stabilized by using its derivative of ZCCF3 as the third component. The new acceptor delivers not only a higher glass transition temperature than Y6 but also have a hyper-miscibility with Y6, contributing to a favorable diffusion-limited Y6: ZCCF3 alloy when blended with polymer donor.

Abstract

Organic solar cells (OSCs) are designed based on a blend of polymer donor and small molecular acceptor whereby the thermodynamic relaxation of the morphology raises the concerns related to operational stability. Herein, it is demonstrated that the classical Y6-based binary device can be stabilized by using its derivative of ZCCF3 as the third component, which is designed with the replacing of the thiadiazole group on Y6 with the trifluoromethyl substituted diazepine unit. ZCCF3 delivers not only higher glass transition temperature (T _g) than Y6 but also have hyper-miscibility with Y6, contributing to a favorable diffusion-limited Y6:ZCCF3 alloy when blended with polymer donor. Consequently, a champion power conversion efficiency of 18.54% is achieved in the optimal PM6: Y6: ZCCF3 devices, which can retain their 80% initial efficiency of up to 360 h. This study highlights the importance of high T _g of the third component and its derived hyper-miscible accepter alloys in achieving highly efficient and stable OSCs.

This work demonstrates that the isotropic coordination capability of hole-transport molecules with Pb²⁺ is crucial to maximally passivate defects, affording robust interface- and light-stable perovskite solar cells. Consequently, the newly developed mCl-spiro[fluorene-9,9′-xanthene] enables devices with a hysteresis index as low as 0.07% and retains 81% of the initial efficiency after 1000 h of continuous illumination at the maximum power point.

Abstract

Interfacial defects are one of the main origins of the hysteresis effect and limit the efficiency and light stability of perovskite solar cells (PSCs). Herein, the authors propose to grant the hole-transport materials’ (HTMs) improved isotropic coordination and defect passivation through simple halogenation, enabling a robust perovskite/hole-transport layer interface while avoiding the use of an external passivation layer. First-principles simulations and experimental results show that the halogenated HTMs offer more isotropic coordination sites for Pb²⁺ ions than the halogen-free ones, thus providing the enhanced passivating ability of defects regardless of their molecular orientation at the surface of perovskite films. Consequently, the PSCs based on the chlorinated spiro[fluorene-9,9′-xanthene]-based HTM show suppressed nonradiative recombination, delivering a remarkable open-circuit voltage (V _OC) enhancement (from 1.07 to 1.14 V) and a minimal hysteresis index of as low as 0.07%. The corresponding cells also show much improved light stability, retaining 81% of the initial efficiency after 1000 h of continuous illumination at the maximum power point. This work demonstrates that a solid isotropic coordination capability of HTMs with Pb²⁺ is critical to forming a robust interface and improving the PSCs’ light stability.

A seed-mediated method is developed to in situ grow 2D perovskite seed for epitaxial growth of 3D perovskite. The epitaxial 3D perovskite film exhibits a preferred [112] direction rather than a traditional [001]. The solar cells based on the [112] preferred perovskite film exhibits a champion efficiency of 24.83% and high stability under ambient, thermal, and light-soaking conditions.

Abstract

Organic-inorganic hybrid perovskite solar cells (PSCs) have been extensively researched as a promising photovoltaic technology, wherein the orientation of the perovskite film plays a crucial role in the power conversion efficiency (PCE) and stability. Here, a seed-mediated method is developed to in situ grow a layer of 2D perovskite seed for epitaxial growth of 3D perovskite atop it to construct a high-quality 2D/3D heterojunction. It is found that the epitaxial 3D perovskite film exhibits a preferred [112] direction, which is different from traditional perovskites with a preferred [001] orientation. The oriented perovskite film consists of large-sized grains with low defect density, long charge-carrier lifetime, and good stability, resulting in efficient PSCs with a champion efficiency of 24.83%. In addition, the devices exhibit high stability under ambient, thermal, and continuous light-soaking conditions. This work provides an effective strategy for achieving high-quality perovskite films with tunable orientation to simultaneously boost the efficiency and stability of PSCs.

Nature Communications, Published online: 20 February 2023; doi:10.1038/s41467-023-36141-8

Lead(II) 2-ethylhexanoate (LDE) is introduced via an antisolvent process into perovskite films to change the kinetics of crystallization, resulting in high-quality perovskite film. The carboxyl functional group coordinates with the Pb cation, reducing the defect concentration. Meanwhile, the long alkyl chains form a protecting layer to prevent chemical attack by water and air, prolonging the lifetime of perovskite devices.

Abstract

The bulk and surface of a perovskite light-harvesting layer are two pivotal aspects affecting its carrier transport and long-term stability. In this work, lead(II) 2-ethylhexanoate (LDE) is introduced via an antisolvent process into perovskite films to change the reaction kinetics of the crystallization process, resulting in a high-quality perovskite film. Meanwhile, a carboxyl functional group with a long alkyl chain coordinates with the Pb cation, reducing the defect density related to unsaturated Pb atoms. Moreover, the long alkyl chains form a protecting layer at the surface of the perovskite film to prevent chemical attack by water and air, prolonging the lifetime of perovskite devices. Consequently, the assembled device demonstrates a power conversion efficiency (PCE) of 24.84%. Both of the thermal and operational stability are significantly improved due to reduced ion-migration channels.

Publication date: May 2023

Source: Journal of Energy Chemistry, Volume 80

Author(s): Zhaoyi Jiang, Binkai Wang, Wenjun Zhang, Zhichun Yang, Mengjie Li, Fumeng Ren, Tahir Imran, Zhenxing Sun, Shasha Zhang, Yiqiang Zhang, Zhiguo Zhao, Zonghao Liu, Wei Chen

Grain-boundary “ligaments” are developed to endow fragile perovskite grain boundaries with toughness, water resistance, and room temperature self-healing properties. Meanwhile, they can also passivate the defects and release the residual tensile strain in perovskite films. The resultant flexible perovskite solar cells achieve a record 23.84% power conversion efficiency and robust mechanical, operational, and ambient stabilities.

Abstract

Flexible perovskite solar cells (pero-SCs) are the best candidates to complement traditional silicon SCs in portable power applications. However, their mechanical, operational, and ambient stabilities are still unable to meet the practical demands because of the natural brittleness, residual tensile strain, and high defect density along the perovskite grain boundaries. To overcome these issues, a cross-linkable monomer TA-NI with dynamic covalent disulfide bonds, H-bonds, and ammonium is carefully developed. The cross-linking acts as “ligaments” attached on the perovskite grain boundaries. These “ligaments” consisting of elastomers and 1D perovskites can not only passivate the grain boundaries and enhance moisture resistance but also release the residual tensile strain and mechanical stress in 3D perovskite films. More importantly, the elastomer can repair bending-induced mechanical cracks in the perovskite film because of dynamic self-healing characteristics. The resultant flexible pero-SCs exhibit promising improvements in efficiency, and record values (23.84% and 21.66%) are obtained for 0.062 and 1.004 cm² devices; the flexible devices also show overall improved stabilities with T ₉₀ >20 000 bending cycles, operational stability with T ₉₀ >1248 h, and ambient stability (relative humidity = 30%) with T ₉₀ >3000 h. This strategy paves a new way for the industrial-scale development of high-performance flexible pero-SCs.

Non-fused ring acceptors for organic solar cells are presented in this Review from the viewpoint of materials design. The cencepts of noncovalent interactions, insertion of sterically hindered side chains, and planarization of the molecular backbone by conformational locking are summarized toward the design of high-performance materials.

Abstract

The prerequisite for commercially viable organic solar cells (OSC) is to reduce the efficiency-stability-cost gap. Therefore, the cost of organic materials should be reduced by minimizing the synthetic steps, yet maintaining the molecular planarity and efficiencies achieved by the fused ring acceptors (FRA). In this respect, developing non-fused ring acceptors (NFRA) with suitable functionalization to favor conformational planarity and effective molecular packing is beneficial and cost-effective. Presently, the power conversion efficiency (PCE) for NFRAs is around 16 %, yet lower than the 19 % achieved for FRAs. Despite their potential, a thorough understanding of the effective structural design of NFRAs is necessary for developing efficient OSCs. This article pays special attention to the molecular design concept for NFRAs developed in the last years and analyzed the approach toward materials design and efficiency improvement, an important step toward technological application.

Nature Communications, Published online: 17 February 2023; doi:10.1038/s41467-023-36652-4

Publication date: June 2023

Source: Journal of Energy Chemistry, Volume 81

Author(s): Lili Gao, Ping Hu, Shengzhong (Frank) Liu

Nature Photonics, Published online: 16 February 2023; doi:10.1038/s41566-022-01151-3

This perspective discusses in-depth the main performance losses, and three current critical issues including crystallization dynamics, defect chemistry, and phase segregation from a bottom-up perspective, in wide-bandgap mixed-halide perovskite solar cells. Five promising prospects are also proposed to guide the research hot spots for next-generation device commercialization.

Abstract

Wide-bandgap (WBG) perovskite solar cells (PSCs) are acknowledged as promising candidates for multijunction tandem and building photovoltaics, which attract broad research interest in related research communities. However, the performance of WBG PSCs based on the mixed-halide perovskites still lags far behind their pure-iodide counterparts because of the complex compositional evolution, huge photovoltage deficits, and intrinsic spectral losses. Here, by comprehensively understanding the representative WBG PSCs, the main “WBG drawbacks” from the device point of view are discussed in-depth and three intrinsic critical issues for the growth of high-quality WBG perovskites are proposed. The prospects for WBG PSCs toward future advancements and commercialization are also presented to guide the coming research hot spots.

A lead-doped titanium-oxo cluster protected by sulfur-containing organic ligands is employed as a molecular model to realize the directional preparation of PbSO₄-PbTi₃O₇ heterostructure at the cathode interlayer in perovskite solar cells (PSCs). The oxygen atoms from the sulfate ion in the heterostructure connect with iodine from the perovskite to boost interfacial electron extraction and reduce charge recombination. An efficiency as high as 24.2 % for the modified PSC is realized, and the stability of the devices is also improved.

Abstract

Typical wide-band gap cathode interlayer materials are difficulty in reducing interface recombination without limiting charge transport in perovskite solar cells (PSCs). Here, a lead-doped titanium-oxo cluster protected by S-containing ligands is introduced at the interface of perovskite and SnO₂. By in situ heating, the cluster is transformed into PbSO₄-PbTi₃O₇ heterostructure. The oxygen atoms from sulfate ion in heterostructure connect with iodine from perovskite to boost interfacial electron extraction and reduce charge recombination. While the yielded metallic interface between PbSO₄ and PbTi₃O₇ promotes the electron transport across the interface. Finally, an efficiency as high as 24.2 % for the modified PSC is obtained. The heterostructure well-stabilize the interface of perovskite and SnO₂, to greatly improve the device stability. This work provides a novel strategy to prepare wide-band gap cathode interlayer by directional transformation of heterometallic oxo clusters.