Chen Weijie

The NaOH-Se intermediate layer is introduced to simultaneously optimize the deep-level trap of the back interface and CZTSSe light absorber. Over 13% efficient CZTSSe thin-film solar cell can be achieved, accompanied by superior carrier transport kinetics.

Abstract

Cu₂ZnSn (S,Se)₄ (CZTSSe), a promising absorption material for thin-film solar cells, still falls short of reaching the balance limit efficiency due to the presence of various defects and high defect concentration in the thin film. During the high-temperature selenization process of CZTSSe, the diffusion of various elements and chemical reactions significantly influence defect formation. In this study, a NaOH-Se intermediate layer introduced at the back interface can optimize Cu₂ZnSnS₄ (CZTS)precursor films and subsequently adjust the Se and alkali metal content to favor grain growth during selenization. Through this back interface engineering, issues such as non-uniform grain arrangement on the surface, voids in bulk regions, and poor contact at the back interface of absorber layers are effectively addressed. This method not only optimizes morphology but also suppresses deep-level defect formation, thereby promoting carrier transport at both interfaces and bulk regions of the absorber layer. Consequently, CZTSSe devices with a NaOH-Se intermediate layer improved fill factor, open-circuit voltage, and efficiency by 13.3%. This work initiates from precursor thin films via back interface engineering to fabricate high-quality absorber layers while advancing the understanding regarding the role played by intermediate layers at the back interface of kesterite solar cells.

Quinoxaline-phosphine oxide-based molecules with strong dipole moments are introduced as cathode interfacial layers of perovskite solar cells (PSCs), enhancing charge-carrier transport and mitigating charge recombination. The modified wide-bandgap PSCs exhibit a high V _oc of 1.31 V and an efficiency of 20.3%, with superior stability, retaining 95% of initial efficiency after 500 h in air, which demonstrate promise for tandem cells.

Abstract

Wide-bandgap perovskite solar cells (PSCs) with high open-circuit voltage (V _oc) represent a compelling and emerging technological advancement in high-performing perovskite-based tandem solar cells. Interfacial engineering is an effective strategy to enhance V _oc in PSCs by tailoring the energy level alignments between the constituent layers. Herein, n-type quinoxaline-phosphine oxide-based small molecules with strong dipole moments is designed and introduce them as effective cathode interfacial layers. Their strong dipole effect leads to appropriate energy level alignment by tuning the work function of the Ag electrode to form an ohmic contact and enhance the built-in potential within the device, thereby improving charge-carrier transport and mitigating charge recombination. The organic interfacial layer-modified wide-bandgap PSCs exhibit a high V _oc of 1.31 V (deficit of <0.44 V) and a power conversion efficiency (PCE) of 20.3%, significantly improved from the device without an interface dipole layer (V _oc of 1.26 V and PCE of 16.7%). Furthermore, the hydrophobic characteristics of the small molecules contribute to improved device stability, retaining 95% of the initial PCE after 500 h in ambient air.

The semitransparent perovskite solar cells are facing challenges regarding phase segregation and operational stability. By reconstructing the light active region, compressive strain is initiated to stabilize lattice and suppress ion migration. The bifacial device yields an equivalent efficiency of 13.97% with an average visible transmittance of 41.58%, and a light utilization efficiency of 5.8%, offering a balance between transparency and photovoltaic performance.

Abstract

Semitransparent perovskite solar cells (ST-PSCs) hold great promise for various commercial applications, including building integrated photovoltaics and tandem solar cells. The all-inorganic perovskite, known for its outstanding optical transparency and thermal stability, emerges as a top contender for ST-PSCs. However, challenges persist due to phase segregation, which hampers charge carrier transport and operational stability. In this study, an approach is proposed to address these challenges by employing strain engineering to reconstruct the perovskite texture, eliminating inhomogeneities within the perovskite film. The crucial role of compressive strain in stabilizing lattice rigidity and suppressing light-induced ion migration is demonstrated. Furthermore, a transparent light-harvesting architecture is devised utilizing a sandwiched layer of gold embedded between MoO₃. This design enhances power generation by efficiently harnessing incident light from both the front and rear panel surfaces. Therefore, bifacial ST-PSCs achieve an equivalent efficiency (η _eq) of 13.97% with an average visible light transmittance of 41.58%, yielding an outstanding light utilization efficiency of up to 5.8%. This research not only advances the understanding of perovskite material phase-segregation behavior but also introduces an effective strategy for enhancing optical gain without compromising the semitransparent characteristics.

A series of polythiophene-based donors are synthesized using direct arylation polycondensation (DArP), highlighting PT4F-Th, which achieves an outstanding power conversion efficiency (PCE) of 16.4% in binary organic solar cells (OSCs). This efficiency sets a new record for DArP-derived donors. Blend film morphology is characterized by X-ray scattering and microscopy, emphasizing the synergistic effects of temperature-dependent aggregation behavior and miscibility.

Abstract

Polythiophenes are the most appealing donor materials in organic solar cells (OSCs) due to their simple chemical structures. However, the top-performance polythiophenes are typically synthesized via Stille polycondensation, which is problematic due to significant toxicity and poor atom economy. By contrast, direct arylation polycondensation (DArP) is an eco-friendly, and atom-efficient alternative for synthesizing conjugated polymers, while the best efficiency for DArP-derived polythiophenes is below 12%. This study reports a series of polythiophene-based donors synthesized via DArP. Among these, PT4F-Th reaches a power conversion efficiency (PCE) of 16.4%, which not only matches the current record for polythiophene-based donor materials, but also marks the highest PCE achieved by DArP-derived donors to date. The superior performance of PT4F-Th is largely attributed to its optimal temperature-dependent aggregation behavior and moderate miscibility with acceptors, along with the highest crystallinity among the candidates, resulting in the most favorable blend film morphology. This study underscores the significant potential of DArP-derived polythiophenes in developing high-performance and eco-friendly OSCs.

The two bottles represent the perovskite lattices of MAPbI₃ and MASn_0.25Pb_0.75I₃, respectively. Upon photoexcitation, polarons are generated within the perovskites. The various balls illustrate polarons with different sizes. In MAPbI₃, the polaron size is larger, resulting in a significantly limited polaron density. Conversely, in MASn_0.25Pb_0.75I₃, the smaller polaron size facilitates a much higher polaron density.

Abstract

Charge carriers in the soft and polar perovskite lattice form so-called polaron quasiparticles, charge carriers dressed with a lattice deformation. The spatial extent of a polaron is governed by the material's electron-phonon interaction strength, which determines charge carrier effective mass, mobility, and the so-called Mott polaron density, that is, the maximum stable density of charge carriers that a perovskite can support. Despite its significance, controlling polaron dimensions has been challenging. Here, experimental substantial tuning of polaron dimensions is reported by lattice engineering, through Pb/Sn substitution in CH₃NH₃Sn_xPb_1−xI₃. The polaron dimension is deduced from the Mott polaron density, which can be composition-tuned over an order of magnitude, while charge carrier mobility occurs through band transport, and remains substantial across all compositions, ranging from 10 s to 100 s cm² V s⁻¹ at room temperature. The effective modulation of polaron size can be understood by considering the bond asymmetry after carrier injection as well as the random spatial distribution of Pb/Sn ions. This study underscores the potential for tailoring polaron dimensions, which is crucial for optimizing applications prioritizing either high charge carrier density or high mobility.

The oxidation process of Nb₂CT _x MXene is methodically simulated at the atomic level and nanosecond timescales, predicting a transition from metal to semiconductor with 44% C atoms replaced by O atoms in Nb₂CT _x . By exploiting MXenes to their derivatives, a promising approach to designing ETL for photovoltaic technologies is demonstrated.

Abstract

In the realm of photovoltaic research, 2D transition metal carbides (MXenes) have gained significant interest due to their exceptional photoelectric capabilities. However, the instability of MXenes due to oxidation has a direct impact on their practical applications. In this work, the oxidation process of Nb₂CT _x MXene in aqueous systems is methodically simulated at the atomic level and nanosecond timescales, which elucidates the structural variations influenced by the synergistic effects of water and dissolved oxygen, predicting a transition from metal to semiconductor with 44% C atoms replaced by O atoms in Nb₂CT _x . Moreover, Nb₂CT _x with varying oxidation degrees is utilized as electron transport layers (ETLs) in perovskite solar cells (PSCs). Favorable energy level alignments with superior electron transfer capability are achieved by controlled oxidation. By further exploring the composites of Nb₂CT _x to its derivatives, the strong interaction of the nano-composites is demonstrated to be more effective for electron transport, thus the corresponding PSC achieves a better performance with long-term stability compared with the widely used ETLs like SnO₂. This work unravels the oxidation dynamics of Nb₂CT _x and provides a promising approach to designing ETL by exploiting MXenes to their derivatives for photovoltaic technologies.

The interfacial carrier transport and energy transfer in 2D/3D perovskite heterostructures are enhanced through the introduction of fluorine atoms on the phenethylammonium (PEA) cation.

Abstract

The interfacial 2D/3D perovskite heterostructures have attracted extensive attention due to their unique ability to combine the high stability of 2D perovskites with the remarkable efficiency of 3D perovskites. However, the carrier transport mechanism within the 2D/3D perovskite heterostructures remains unclear. In this study, the carrier transport dynamics in 2D/3D perovskite heterostructures through a variety of time-resolved spectroscopic measurements is systematically investigated. Time-resolved photoluminescence results reveal nanosecond hole transfer from the 3D to 2D perovskites, with enhanced efficiency through the introduction of fluorine atoms on the phenethylammonium (PEA) cation. Transient absorption measurements unveil the ultrafast picosecond electron and energy transfer from 2D to 3D perovskites. Furthermore, it is demonstrated that the positioning of fluorination on the PEA cations effectively regulates the efficiency of charge and energy transfer within the heterostructures. These insightful findings shed light on the underlying carrier transport mechanism and underscore the critical role of cation fluorination in optimizing carrier transport within 2D/3D perovskite heterostructure-based devices.

In this study, efficient and stable perovskite solar cells (PSCs) are fabricated utilizing chemical bath deposition (CBD) SnO₂ electron transport layers and 3D/2D perovskite heterojunctions. The rate of degradation of perovskite films heated in air is retarded by the 3D/2D heterojunctions. The hydrophobic surfaces of 2D passivators enhance the long-term stability of PSCs.

Abstract

Chemical bath deposition (CBD) is an effective technique used to produce high-quality SnO₂ electron transport layers (ETLs) employed in perovskite solar cells (PSCs). By optimizing the CBD process, high-quality SnO₂ films are obtained with minimal oxygen vacancies and close energy level alignment with the perovskite layer. In addition, the 3D perovskite layers are passivated with n-butylammonium iodide (BAI), iso-pentylammonium iodide (PNAI), or 2-methoxyethylammonium iodide (MOAI) to form 3D/2D heterojunctions, resulting in defect passivation, suppressing ion migration and improving charge carrier extraction. As a result of these heterojunctions, the power conversion efficiency (PCE) of the PSCs increased from 21.39% for the reference device to 23.70% for the device containing the MOAI-passivated film. The 2D perovskite layer also provides a hydrophobic barrier, thus enhancing stability to humidity. Notably, the PNAI-based device exhibited remarkable stability, retaining approximately 95% of its initial efficiency after undergoing 1000-h testing in an N₂ environment at room temperature.

A highly transparent passivating contact (TPC) for high-efficiency crystalline silicon (c-Si) solar cells featuring a silicon oxide (SiOx) tunneling passivating layer and aluminum-doped zinc oxide (AZO) electron-selective transporting layer is designed. This TPC demonstrates exceptional passivation and contact performance, achieving an efficiency of 23.17% when applied to an n-type c-Si solar cell.

Abstract

A highly transparent passivating contact (TPC) used for high-efficiency crystalline silicon (c-Si) solar cells should meet several key criteria: high optical transparency, excellent c-Si surface passivation, low contact resistivity, and a low-temperature fabrication process suitable for device integration. Here, a simple TPC is developed structure consisting of a silicon oxide (SiO_x) tunneling passivating layer and an aluminum doped zinc oxide (AZO) electron-selective transporting layer (SiO_x/AZO). This TPC demonstrated remarkable passivation quality with a low contact recombination current density of below 2.2 fA cm⁻², an implied open-circuit voltage of close to 740 mV and a contact resistivity below 20 mΩ·cm² when contact with lightly doped n-type c-Si. This excellent passivation performance can be attributed to improved interfacial hydrogen chemical passivation and the field-effect passivation induced by the highly Al-doped ZnO film. Demonstrated n-type c-Si solar cells using full-area SiO_x/AZO rear contacts achieved a significant efficiency of 23.17%. Further power loss analysis based on numerical simulations outlines the pathway to achieving efficiencies exceeding 26%.

An industrial-level sub-micron random pyramid (sMRP) structure with low reflectance is introduced on the front side of a TOPCon solar cell. These sMRP-textures facilitate the formation of a high-quality perovskite film with larger grain sizes and fewer internal pinholes. A proof-of-concept perovskite/TOPCon tandem solar cell (TSC) featuring sMRP textures exhibits a high efficiency of 28.67%, providing a promising approach for commercial TSCs.

Abstract

Texturing silicon solar cells with micro/nano-structures is crucial for achieving outstanding optical performance in perovskite/silicon tandem solar cells (TSCs). However, ensuring excellent electrical properties remains a challenge due to reduced passivation quality of the bottom silicon sub-cells and difficulties in perovskite formation on textured substrates. Here, an industrial-level sub-micron random pyramid (sMRP) structure on the front side of a tunnel oxide passivating contact (TOPCon) solar cell using a simple alkaline texturing process is presented, resulting in excellent optical and electrical properties. Through meticulous fabrication process tuning, uniform sMRP textures with a size of 0.6–0.8 µm are achieved, exhibiting low reflectance comparable to industrial-level micron random pyramid (MRP) structures. Optimizing annealing temperatures of double-sided TOPCon structures textured with front-sided sMRP and rear-sided MRP, yields high passivation quality, with a remarkable implied open-circuit voltage (iV _OC) of 713 mV. Furthermore, the sMRP-textured surface facilitates the formation of a high-quality perovskite film with larger grain sizes and fewer internal pinholes compared to the polished counterpart. Consequently, a proof-of-concept p-i-n typed perovskite/TOPCon TSC featuring sMRP textures obtains an outstanding efficiency of 28.67%, providing a promising approach for the commercial production of high-efficiency perovskite/TOPCon TSCs.

Publication date: 1 December 2024

Source: Nano Energy, Volume 131, Part A

Author(s): Hao Hou, Wenxuan Wang, Qian Kang, Jianqiu Wang, Zhihao Chen, Yafei Wang, Yong Cui, Yue Yu, Ji Zhu, Hui Yan, Jianhui Hou

Publication date: November 2024

Source: Nano Energy, Volume 130

Author(s): Yingjie Sun, Lu Zhang, Miao Zhang, Wenqing Zhang, Sang Young Jeong, Xiaotao Hao, Han Young Woo, Xiaoling Ma, Fujun Zhang, Wai-Yeung Wong

Publication date: November 2024

Source: Nano Energy, Volume 130

Author(s): Tianyu Hu, Xufan Zheng, Cong Xiao, Junchi Su, Aziz Saparbaev, Ming Wan, Jingnan Wu, Huimin Xiang, Yun Yu, Ergang Wang, Xunchang Wang, Renqiang Yang

Publication date: November 2024

Source: Nano Energy, Volume 130

Author(s): Xianyong Zhou, Jiawen Wu, Jie Zeng, Deng Wang, Jinbo Chen, Meiqing Zhang, Wenbo Peng, Zhixin Liu, Yong Zhang, Luozheng Zhang, Lei Yan, Chang Liu, Xingzhu Wang, Baomin Xu

Three thienopyrazine-based organic molecules as self-assembled monolayers (SAMs) were developed and deposited on NiOx films for tin-based perovskite solar cells. Using NiOx as interlayer can modify the hydrophilicity and surface roughness of the ITO substrate. The two-step method was applied to enable better quality of the tin perovskite layer grown on the NiOx/SAM substrates, ultimately achieving a power conversion efficiency of 7.7 %.

Abstract

Three functionalized thienopyrazines (TPs), TP-MN (1), TP-CA (2), and TPT-MN (3) were designed and synthesized as self-assembled monolayers (SAMs) deposited on the NiOx film for tin-perovskite solar cells (TPSCs). Thermal, optical, electrochemical, morphological, crystallinity, hole mobility, and charge recombination properties, as well as DFT-derived energy levels with electrostatic surface potential mapping of these SAMs, have been thoroughly investigated and discussed. The structure of the TP-MN (1) single crystal was successfully grown and analyzed to support the uniform SAM produced on the ITO/NiOx substrate. When we used NiOx as HTM in TPSC, the device showed poor performance. To improve the efficiency of TPSC, we utilized a combination of new organic SAMs with NiOx as HTM, the TPSC device exhibited the highest PCE of 7.7 % for TP-MN (1). Hence, the designed NiOx/TP-MN (1) acts as a new model system for the development of efficient SAM-based TPSC. To the best of our knowledge, the combination of organic SAMs with anchoring CN/CN or CN/COOH groups and NiOx as HTM for TPSC has never been reported elsewhere. The TPSC device based on the NiOx/TP-MN bilayer exhibits great enduring stability for performance, retaining ~80 % of its original value for shelf storage over 4000 h.

Two electron-deficient isomers, 4,5-difluorobenzo-c-1,2,5-thiadiazole (SF-1) and 5,6-difluorobenzo-c-1,2,5-thiadiazole (SF-2), were designed as solid additives to optimize the properties of PM6 : PY-DT blend. Compared to the as-cast device, SF-1- and SF-2-treated devices displayed regulated fibrillar donor-acceptor network, improved exciton diffusion length, and thus enhanced power conversion efficiencies approaching 19 %, which is one of rare solid additives for high-performance all-polymer organic solar cells.

Abstract

Disordered polymer chain entanglements within all-polymer blends limit the formation of optimal donor-acceptor phase separation. Therefore, developing effective methods to regulate morphology evolution is crucial for achieving optimal morphological features in all-polymer organic solar cells (APSCs). In this study, two isomers, 4,5-difluorobenzo-c-1,2,5-thiadiazole (SF-1) and 5,6-difluorobenzo-c-1,2,5-thiadiazole (SF-2), were designed as solid additives based on the widely-used electron-deficient benzothiadiazole unit in nonfullerene acceptors. The incorporation of SF-1 or SF-2 into PM6 : PY-DT blend induces stronger molecular packing via molecular interaction, leading to the formation of continuous interpenetrated networks with suitable phase-separation and vertical distribution. Furthermore, after treatment with SF-1 and SF-2, the exciton diffusion lengths for PY-DT films are extended to over 40 nm, favoring exciton diffusion and charge transport. The asymmetrical SF-2, characterized by an enhanced dipole moment, increases the power conversion efficiency (PCE) of PM6 : PY-DT-based device to 18.83 % due to stronger electrostatic interactions. Moreover, a ternary device strategy boosts the PCE of SF-2-treated APSC to over 19 %. This work not only demonstrates one of the best performances of APSCs but also offers an effective approach to manipulate the morphology of all-polymer blends using rational-designed solid additives.

A 15.2% efficient monolithically integrated InGaP/GaAs/Si triple-junction solar cell by using In_0.10Al_0.16Ga_0.74As digital-alloy dislocation filter layers is demonstrated. Impacts of threading dislocations and residual thermal tension on the InGaP/GaAs/Si cells are investigated by comparing them to co-grown InGaP/GaAs tandem cells on GaAs. A realistic pathway toward 33% efficient epitaxially grown III–V/Si triple-junction solar cells is proposed.

Direct epitaxy of III−V materials on Si is a promising approach for highly stable, scalable, and efficient Si-based multijunction solar cells. However, challenges lie in overcoming epitaxial dislocations and residual thermal strain generated by lattice constant and thermal-expansion-coefficient mismatches, respectively. Herein, a 15.2% efficient InGaP/GaAs/Si triple-junction solar cell with an open-circuit voltage of 2.36 V by using In_0.10Al_0.16Ga_0.74As digital-alloy dislocation filter layers is first demonstrated. The filter layers are utilized in the n-GaAs buffer on Si to reduce threading dislocation density to 4 × 10⁷ cm⁻² while maintaining optical transparency to Si bottom cell. Then, the impacts of threading dislocations and residual tension on InGaP/GaAs/Si cells are systematically investigated by comparing them to the co-grown InGaP/GaAs tandem cells on a native GaAs substrate. Based on the comparative analysis, a strategy to suppress material deformation and defect formation toward 30% efficient InGaP/GaAs/Si triple-junction solar cells is proposed.

The molecular synergistic effect enabled by piperazine-1-carboxamide hydrochloride and 1,3-propane-diammonium iodide facilitates excellent energy level alignment and reduces non-radiative recombination losses and light-induced phase segregation. The target perovskite/perovskite/silicon triple-junction tandem solar cell obtains an open-circuit voltage of 3.07 V and a champion power conversion efficiency of 25.2% (for a 1.035 cm² aperture area).

Abstract

Perovskite/perovskite/silicon triple-junction tandem solar cells (TSCs) hold promise for high power conversion efficiencies (PCE). However, the efficiency is still relatively low due to the non-radiative recombination losses in wide-bandgap top cells. These losses, attributed to the interface defect states and energy level mismatches, present considerable challenges to realizing high-performance and stable TSCs. Here, the molecular synergistic effect (MSE) is exploited to passivate interface in 1.95 eV top cells. Piperazine-1-carboxamide hydrochloride (PCACl) is combined, which possesses strong dipole moments and passivating functional groups that can bind with two neighboring uncoordinated lead ions and form hydrogen bonds with halide atoms at perovskite surface, with 1,3-propane-diammonium iodide, which can reduce interface recombination through field-effect passivation. The MSE enabled by PCACl and PDAI₂ facilitates excellent energy level alignment and reduces non-radiative recombination losses and light-induced phase segregation. Finally, the target perovskite/perovskite/silicon triple-junction TSC obtains an open-circuit voltage of 3.07 V and a champion PCE of 25.2% (for a 1.035 cm² aperture area).

Scanning probe microscopy (SPM) has enabled significant new insights into solar cell materials' nanoscale and microscale properties and underlying working principles of photovoltaic and optoelectronic technology. This review provides an overview of SPM measurement capabilities and attainable insight, focusing on recently widely investigated halide perovskite materials.

Abstract

Scanning probe microscopy (SPM) has enabled significant new insights into the nanoscale and microscale properties of solar cell materials and underlying working principles of photovoltaic and optoelectronic technology. Various SPM modes, including atomic force microscopy, Kelvin probe force microscopy, conductive atomic force microscopy, piezoresponse force microscopy, and scanning near-field optical microscopy, can be used for the investigation of electrical, optical and chemical properties of associated functional materials. A large body of work has improved the understanding of solar cell device processing and synthesis in close synergy with SPM investigations in recent years. This review provides an overview of SPM measurement capabilities and attainable insight with a focus on recently widely investigated halide perovskite materials.

A series of thiophene oligomers are designed and synthesized through coupling reaction by using polyoxometalates as the oxidizing reagents. By using the oligothiophenes TO-P2 as hole-transporting material, the organic solar cell (OSC) exhibits a photovoltaic efficiency of 17.25%. Moreover, the 1 cm² OSC shows a photovoltaic efficiency of 15.0% when using a blade-coated TO-P2 film.

Hole-transporting layer (HTL) materials with sufficient hole collection ability, noncorrosive nature, and easy preparation are strongly desired for the field of organic solar cells (OSCs). The development of new materials and synthetic methods has been proved to be the essential approach to improve the HTL performances. Herein, a series of thiophene oligomers TO-P1, TO-P2, and TO-P3 are designed and synthesized through coupling reaction by using the polyoxometalates as the oxidizing reagents. The thiophene oligomers can be readily synthesized under ambient condition with high yield. Among the as-prepared thiophene oligomers, TO-P2 exhibits neutral pH, sufficient work function, and high conductivity, endowing the HTL with excellent hole collection ability. Also, TO-P2 possesses good chemical stability and satisfied solution processability, which is important for practical use. By using TO-P2 as HTL, OSC shows a photovoltaic efficiency of 17.25%. Furthermore, TO-P2 is a universal HTL that can be used to fabricate efficient OSCs with various active layers. More importantly, TO-P2 shows good compatibility with large-area processing technique. A 1 cm² OSC is fabricated by using a blade-coated TO-P2 HTL, exhibiting a power conversion efficiency of 15.0%. The easy preparation and noncorrosive nature endow TO-P2 with great potential application in OSCs.

A molecule anchoring strategy is proposed to construct Pb–Sn perovskite film with vertically aligned crystals and optimized interfaces, which produces narrow-bandgap perovskite solar cells with a champion power conversion efficiency (PCE) of 22.3% and a record-high fill factor of 82.14%. Corresponding four-terminal (4T) all-perovskite tandem device achieves a PCE of 27.1%.

Abstract

Narrow-bandgap (NBG) Pb–Sn perovskites are ideal candidates as rear subcell in all-perovskite tandem solar cells. Because Pb–Sn perovskites contain multiple components, the rational regulation of vertical structure and both interfaces of the film is primarily crucial to achieve high-performing NBG perovskite solar cells (PSCs). Herein, a molecule anchoring strategy is developed to in situ construct Cs_0.1MA_0.3FA_0.6Pb_0.5Sn_0.5I₃ perovskite film with vertically aligned crystals and optimized interfaces. Specifically, l-alanine methyl ester is developed as an anchoring additive to induce the vertical crystal growth, while PEA₂PbI₃SCN film is introduced to promote the homogeneous crystallization at the buried interface via SCN− anchoring with cations. Further ethylenediamine dihalides (EDA(I/Cl)₂) post-treatment leads to the gradient energy level alignment on the film surface. Pb–Sn PSCs based on such film show efficient charge transport and extraction, producing a champion power conversion efficiency (PCE) of 22.3% with an impressive fill factor of 82.14%. Notably, combining with semitransparent 1.78 eV wide-bandgap PSCs, the four-terminal all-perovskite tandem device achieves a PCE of 27.1%. This work opens up a new pathway to boost the performance of Pb–Sn PSCs and their tandem devices.

An ADA-type small molecule acceptor is used to construct a dimerized acceptor (DMT-HF) which is featured with a high glass transition temperature and a low diffusion coefficient. When blended with a wide band gap copolymer, the resulting DMT-HF-based polymer solar cell exhibits an excellent efficiency of 17.17 % and outstanding thermal stability.

Abstract

As the simplest oligomeric acceptors, dimerized acceptors (DAs) are easier to synthesize, and more importantly, they can retain good intermolecular interaction and photovoltaic properties of their parent small-molecule acceptors (SMAs). Nevertheless, currently most efficient DAs are derived from banana-shaped acceptors and they might suffer from inferior device stability with high diffusion coefficients. Herein, we design and synthesize two planar DAs (DMT-FH and DMT-HF) by bridging two linear-shaped M-series SMAs with a thiophene unit. The effects of fluorination position on the diffusion coefficients, power conversion efficiencies (PCEs) and stability of the DAs are systematically studied. Our results suggest that DMT-HF with fluorination on the ending indanone groups shows enhanced intermolecular interactions, improved PCE and stability compared with the counterpart (DMT-FH) with fluorination on the central indanone groups. Further optimization on the DMT-HF-based devices yields an outstanding PCE of 17.17 %, which is the highest among all linear-shaped SMA-based DAs. Notably, with the low diffusion coefficient (3.36×10⁻²⁴ cm² s⁻¹) of DMT-HF, the resulting device retains over 93 % of the initial PCE after 5000 h of continuous heating at 85 °C, suggesting its excellent thermal stability. The results highlight the importance of intermolecular interaction and fluorination for achieving efficient and stable polymer solar cells.

Lewis base 2D covalent organic frameworks, TFT-COF and TT-COF are applied to mitigate energetic mismatches and introduce effective n-type surface energetics and band bending via cyclic, multi-site chelation with undercoordinated lead ions. Such a multi-site chelation effect enables a high efficiency of 25.64 % (certified 24.94 %) and excellent stability in the inverted perovskite solar cells.

Abstract

Trap-assisted non-radiative recombination losses and moisture-induced degradation significantly impede the development of highly efficient and stable inverted (p–i–n) perovskite solar cells (PSCs), which require high-quality perovskite bulk. In this research, we mitigate these challenges by integrating thermally stable perovskite layers with Lewis base covalent organic frameworks (COFs). The ordered pore structure and surface binding groups of COFs facilitate cyclic, multi-site chelation with undercoordinated lead ions, enhancing the perovskite quality across both its bulk and grain boundaries. This process not only reduces defects but also promotes improved energy alignment through n-type doping at the surface. The inclusion of COF dopants in p–i–n devices achieves power conversion efficiencies (PCEs) of 25.64 % (certified 24.94 %) for a 0.0748-cm² device and 23.49 % for a 1-cm² device. Remarkably, these devices retain 81 % of their initial PCE after 978 hours of accelerated aging at 85°C, demonstrating remarkable durability. Additionally, COF-doped devices demonstrate excellent stability under illumination and in moist conditions, even without encapsulation.

An in situ ligand-management strategy is proposed to achieve one-step synthesis and passivation of SnO₂ nanoparticles by introducing diethyl 2-chloromalonate (DCMA). Compared with the post-treatment process, this intrinsic DCMA-passivated SnO₂ exhibits stronger surface chemical stability. The PSCs based on DCMA-SnO₂ achieve a champion PCE of 25.39% for small cells and 20.61% for solar modules (23.25 cm²) and demonstrate excellent shelf-life/light soaking stability.

Abstract

Tin oxide (SnO₂) with high conductivity and excellent photostability has been considered as one of the most promising materials for efficient electron transport layer (ETL) in perovskite solar cells (PSCs). Among them, SnO₂ nanoparticles (NPs) dispersions have been extensively utilized due to their facile film formation. However, the inherent defects and agglomeration issues of SnO₂ NPs, as well as the limited tunability and instability of the post-treatment process for surface/interface engineering strategy, still hinder its further applications. Herein, a ligand-management strategy implemented during the in situ synthesis of NPs that can effectively achieve uniform modification of NPs is proposed. During the synthesis of SnO₂ NPs, the grafting reaction between diethyl 2-chloromalonate (DCMA) and the surface of SnO₂ NPs is completed. Compared with the post-treatment process, this intrinsic DCMA-passivated SnO₂ (DCMA-SnO₂) effectively reduces the trap state density at the interface between perovskite and ETL while enhancing surface chemical stability. Consequently, PSCs based on DCMA-SnO₂ achieve a champion PCE of 25.39% for small cells (active area of 0.0655 cm²) and 20.61% for solar modules (active area of 23.25 cm²), demonstrating excellent shelf-life/light soaking stability (advanced level of ISOS stability protocols). This ligand-management strategy exhibits significant application potential in preparing high-efficiency large-area PSCs.