Chen Weijie

This work provides effective small molecule regulatory strategy by using 2,6-pyridinedicarboxamide (PC) to regulate the crystallization kinetics of CsPbI_2.75Br_0.25 inorganic perovskite, prolong the annealing time in air, passivate uncoordinated Pb²⁺. Eventually, a record PCE of 22.07% with high V _OC 1.342 V is achieved based on n–i–p inorganic perovskite solar cells (IPSCs). The n–i–p inorganic perovskite/silicon tandem solar cells (IPTSCs) also achieve a PCE of 27.27% with an impressive V_OC of 2.024 V.

Abstract

Tandem solar cells combining perovskite and silicon have witnessed rapid development in recent years. However, the top cell, utilizing wide-bandgap perovskite as absorbers generally suffer significant open-circuit voltage (V _OC) deficit, particularly for inorganic perovskite, which poses a considerable obstacle to enhancing the power conversion efficiency (PCE). Here, a modulation strategy by using 2,6-pyridinedicarboxamide (PC), the crystallization kinetics of inorganic perovskite film can be effectively regulated, specifically manifested as a relatively longer annealing time in the air, resulting in sufficient growth for the inorganic perovskite grains. Additionally, PC can effectively in situ passivate uncoordinated Pb²⁺, suppressing the non-radiative recombination of charge carriers. Eventually, a record PCE of 22.07% is achieved based on n–i–p inorganic perovskite solar cells (IPSCs), which also demonstrate the highest V _OC above 1.34 V (1.71 eV of bandgap). More importantly, the unencapsulated IPSCs show enhanced thermal stability and photostability. Furthermore, the n–i–p IPSCs are also applied to inorganic perovskite/silicon tandem solar cells (IPTSCs), a PCE of 27.27% and an impressive V _OC of 2.024 V are obtained.

Nature Energy, Published online: 25 April 2024; doi:10.1038/s41560-024-01523-9

Exceeding 26.5%-efficient all flexible Perovskite/CIGS Tandem solar cell is achieved by all-round passivation strategy termed Dual Passivation at Grains and Interfaces which improve film crystallinity and maximize the passivation of defects at various locations within the solar cell structure, effectively minimizing nonradiative recombination losses.

Abstract

The perovskite/Cu(InGa)Se₂ (CIGS) tandem solar cells (TSCs) presents a compelling technological combination poised for the next generation of flexible and lightweight photovoltaic (PV) tandem devices, featuring a tunable bandgap, high power conversion efficiency (PCE), lightweight flexibility, and enhanced stability and durability. Over the years, the imperative to enhance the performance of wide bandgap (WBG) perovskite solar cells (PSCs) has grown significantly, particularly in the context of a flexible tandem device. In this study, an all-round passivation strategy known as Dual Passivation at Grains and Interfaces (DPGI) is introduced for WBG PSCs in perovskite/CIGS tandem structures. The implementation of DPGI is tailored to improve film crystallinity and passivate defects across the solar cell structure, leading to a substantial performance enhancement for WBG PSCs. Subsequently, both rigid and flexible tandem devices are assembled. Impressively, a fully flexible 4T perovskite/CIGS TSCs is successfully fabricated with a PCE of 26.57%, making it the highest value in this field and highlighting its potential applications in the next generation of flexible lightweight PV tandem devices.

In situ cyclized polyacrylonitrile (CPAN) is developed as an electron selective layer (ESL) for highly efficient and stable n-i-p PSCs. The CPAN layer possesses n-type semiconductor properties with a high electron mobility of 4.13×10⁻³ cm² V⁻¹ s⁻¹, and is insoluble in common solvents. The resultant PSC affords a power conversion efficiency of 23.12 % with high operational stability.

Abstract

In situ cyclized polyacrylonitrile (CPAN) is developed to replace n-type metal oxide semiconductors (TiO₂ or SnO₂) as an electron selective layer (ESL) for highly efficient and stable n-i-p perovskite solar cells (PSCs). The CPAN layer is fabricated via facile in situ cyclization reaction of polyacrylonitrile (PAN) coated on a conducting glass substrate. The CPAN layer is robust and insoluble in common solvents, and possesses n-type semiconductor properties with a high electron mobility of 4.13×10⁻³ cm² V⁻¹ s⁻¹. With the CPAN as an ESL, the PSC affords a power conversion efficiency (PCE) of 23.12 %, which is the highest for the n-i-p PSCs with organic ESLs. Moreover, the device with the CPAN layer holds superior operational stability, maintaining over 90 % of their initial efficiency after 500 h continuous light soaking. These results confirm that the CPAN layer would be a desirable low-cost and efficient ESL for n-i-p PSCs and other photoelectronic devices with high performance and stability.

A novel donor–acceptor (D-A) copolymer by incorporating 3,3′-difluoro-2,2′-bithiophene is synthesized. Introducing 3,3′-difluoro-2,2′-bithiophene unit introduces intramolecular F···S noncovalent interactions, which can enhance the planarity of the polymer chain, thereby improve molecular packing, crystallinity, and hole mobility. Finally, a photoelectric conversion efficiency (PCE) of 17.03% is achieved. This work can provide a new strategy for the design and synthesis of polymer donor materials.

Abstract

In this study, two novel donor–acceptor (D–A) copolymers are designed and synthesized, DTBT-2T and DTBT-2T2F with 2,2′-bithiophene or 3,3′-difluoro-2,2′-bithiophene as the donor unit and dithienobenzothiadiazole as the acceptor unit, and used them as donor materials in non-fullerene organic solar cells (OSCs). Due to enhanced planarity of polymer chains resulted by the intramolecular F···S noncovalent interactions, the incorporation of 3,3′-difluoro-2,2′-bithiophene unit instead of 2,2′-bithiophene into the polymers can enhance their molecular packing, crystallinity and hole mobility. The DTBT-2T:L8-BO based binary OSCs deliver a power conversion efficiency (PCE) of only 9.71% with a V _oc of 0.78 V, a J _sc of 20.69 mA cm⁻² _, and an FF of 59.67%. Moreover, the introduction of fluoro atoms can lower the highest occupied molecular orbital levels. As a result, DTBT-2T2F:L8-BO based single-junction binary OSCs exhibited less recombination loss, more balanced charge mobility, and more favorable morphology, resulting in an impressive PCE of 17.03% with a higher V _oc of 0.89 V, a J _sc of 25.40 mA cm⁻², and an FF of 75.74%. These results indicate that 3,3′-difluoro-2,2′-bithiophene unit can be used as an effective building block to synthesize high performance polymer donor materials. This work greatly expands the selection range of donor units for constructing high-performance polymers.

The A–DA’D–A conjugated backbones as the acceptor segments to synthesize two novel molecular dyads (SM-1Y and SM-2Y) are introduced. The SM-2Y-based device demonstrates promising device efficiency and operational stability.

Single-molecular organic photovoltaics (SMOPVs), which are based on monadic systems containing donor (D) and acceptor (A) molecule blocks that facilitate exciton dissociation, offer obvious advantages over binary or multicomponent bulk-heterojunction (BHJ) systems, including simplified cell fabrication, stabilized morphology of the D/A interface, and extended device operation lifetime. However, limited by the development of A blocks, the power conversion efficiency (PCE, ≈5%) of SMOPVs based on molecular D–A dyads still lags conventional BHJ OPVs (over 19%). Herein, by introducing a narrow-bandgap A–DA’D–A conjugated backbone as the A-block, combined with the linear D-block BDT-3T-R and flexible alkyl chain linker, two molecular dyads, SM-1Y (one D-block and one A-block) and SM-2Y (one D-block and two A-blocks), are designed and developed. Due to superior absorption spectra and better molecular stacking compared to SY-1Y, SM-2Y-based SMOPV delivers a PCE of 8.13%, which is the highest value in the SMOPV reported thus far. Note that both SM-1Y and SM-2Y devices show much better storage and photostability stability as compared to the control BDT-3T-C6:Y18-C3 binary system.

 The effect of molecular bonding state on antioxidation properties is investigated. A perplexing phenomenon regarding accelerated oxidation in acrylic acid is discovered that deviated from conventional Lewis base–acid reaction. The underlying insights into the deprotonation of acrylic acid followed by the formation of ionic bonding form are provided, which resulted in amplifying the delocalization effect of electrons of Sn²⁺.

Abstract

The improvement of photovoltaic and stability performance of tin (Sn)-based halide perovskite solar cells is impeded by notorious oxidation issues and Anderson localization. Despite previous implements in antioxidation through the incorporation of Lewis base additives, there still exist ongoing uncertainties surrounding its complex interaction mechanisms. A perplexing phenomenon regarding accelerated oxidation in acrylic acid is discovered that deviates from conventional Lewis base–acid reaction. The underlying insights into the deprotonation of acrylic acid followed by the formation of a “tripod” ionic bonding form are provided, which results in amplifying the delocalization effect of electrons of Sn²⁺. Furthermore, with the assistance of acrylamide and acrolein, synergistic enhancement in terms of the antioxidation and suppression of Anderson localization can be achieved — a concept referred to as “Dual Synergistic Engineering”. This suppresses the oxidation of Sn²⁺ and reduces Sn⁴⁺ content by ≈76%. Meanwhile, the diffusion length is prolonged significantly from 195.9 to 458.9 nm. The optimized all-inorganic Sn/Pb-based perovskite solar cells exhibit a power conversion efficiency of above 14% with enhanced stability. These findings provide an alternative viewpoint for comprehending the impact of chemical interaction on oxidation and crystal growth in Sn/Pb-based perovskites.

Highly efficient and stable perovskite solar cells are developed by incorporating a polyfluorinated organic diammonium salt which cann't generate low-dimensional perovskites into the lead iodide precursor to change the arrangement of the lead iodide crystals. The resulting high-quality perovskite film with large grain size boost the efficiencies to 24.70 % and 21.04 % for cell (0.06 cm²) and module (100 cm²), respectively.

Abstract

The inefficient conversion of lead iodide to perovskite has become one of the major challenges in further improving the performance of perovskite solar cells fabricated by the two-step method. Herein, the discontinuous lead iodide layer realized by introduction of a polyfluorinated organic diammonium salt, octafluoro-([1,1′-biphenyl]-4,4′-diyl)-dimethanaminium (OFPP) iodide which does not form low-dimensional perovskites, can enable the satisfactory conversion of lead iodide into perovskite, leading to meliorated crystallinity and enlarged grains in the OFPP modulated perovskite (OFPP-PVK) film. Combined with the effective defect passivation, the OFPP-PVK films show enhanced charge mobility and suppressed charge recombination. Accordingly, the OFPP-based perovskite solar cells exhibit a champion efficiency of 24.76 % with better device stability. Moreover, a superior efficiency of 21.04 % was achieved in a large-area perovskite module (100 cm²). Our work provides a unique insight into the function of organic diammonium additive in boosting photovoltaic performance.

Publication date: July 2024

Source: Nano Energy, Volume 126

Author(s): Hui Sheng, Shizhao Liu, Xiao Kang, Jianan Niu, Adeoba Abdullah Adewale, Shuguang Wen, Chunming Yang, Xichang Bao, Mingliang Sun

High-quality SnO₂ films were prepared through synergistic modified SnO₂ with rubidium fluoride and 4-carboxy-3-fluorobenzoboric acid (FBCA). This strategy improves charge transport by passivating interfacial defects and optimizing energy level alignment, and FBCA can effectively promote the crystallization of perovskite (PVK) films. Therefore, the PVK solar cell with the synergistic modified SnO₂ obtain a champion efficiency of 21.92%.

Element doping and interface modification strategy are effective methods to regulate the electrical properties of SnO₂ electron transport material, SnO₂/perovskite (PVK) interface, and PVK crystal growth. Herein, rubidium fluoride (RbF) is introduced into SnO₂ colloidal dispersion, and then an ultra-thin layer of 4-carboxy-3-fluorobenzoboric acid (FBCA) is applied to the SnO₂ layer surface. This synergistic modification strategy can improve the electrical conductivity of the electron transport layer, increase the chemical connection of the buried interface, improve the crystallization and grain growth of PVK, and thus promote the performance and stability of devices. The results show that the PVK solar cells (PSCs) with the synergistic-modified SnO₂ electron transport material (M-SnO₂) obtain an optimum power conversion efficiency of 21.92% and the unencapsulated PSCs sustain 91% and 87% of the original value, which stored in a nitrogen atmosphere and ambient atmosphere (25 ± 5 °C, 30–50% relative humidity) more than 1000 h, respectively.

Using industrial N₂O as in-situ oxygen dopant source during plasma enhanced chemical vapor deposition (PECVD), p-type oxygen-incorporated poly-Si (poly-SiO _x ) shows reduced refractive index and ignorable extinction coefficient over 700–1200 nm wavelength, yielding reduced reflection and higher transmission. Using bottom cell with p-type poly-SiO _x in front-side passivating contact, the short-circuit current density and efficiency of a perovskite/silicon tandem cell increases by ≈0.32 mA cm⁻² and ≈0.8%, respectively.

Tunnel oxide passivated contact (TOPCon) silicon solar cells have been developed and transferred into industrial mass production, which is beneficial to the future production of perovskite/silicon tandem solar cells (TSCs) in a large scale. However, the doped polycrystalline silicon (poly-Si) layer in the poly-Si-based passivating contact structure yields a profound optical loss from reflection and parasitic absorption, which obstacles the efficiency promotion of TSCs. In this work, the optical property of poly-Si is improved by in-situ oxygen incorporation using plasma enhanced chemical vapor deposition (PECVD) with nitrous oxide (N₂O) as the oxygen source. The p-type oxygen-incorporated poly-Si (poly-SiO _x ) shows a reduced refractive index and extinction coefficient over 700–1200 nm wavelength, leading to a reduced reflection, a lower parasitic absorption and a higher transmission. After applying an optimized p-type oxygen-incorporated poly-Si in the front-side poly-Si passivating contact structure of c-Si bottom cell, the short-circuit current density and efficiency of a perovskite/c-Si tandem cell increases by ≈0.32 mA cm⁻² and ≈0.8%, respectively, leading to 25.12% tandem cell efficiency.

In this study, IDTR and binary systems have complementary absorption characteristics and cascade alignment. The morphology analysis shows that the introduction of IDTR makes it have strong crystallinity, good miscibility, and reasonable vertical phase distribution, thus achieving higher and more balanced charge transport behavior. The PCE is significantly improved, and the continuously illuminated T₈₀ successfully achieved excellent device stability of nearly 400 h.

Abstract

The strategic and logical development of the third component (guest materials) plays a pivotal and intricate role in improving the efficiency and stability of ternary organic solar cells (OSCs). In this study, a novel guest material with a wide bandgap, named IDTR, is designed, synthesized, and incorporated as the third component. IDTR exhibits complementary absorption characteristics and cascade band alignment with the PM6:Y6 binary system. Morphological analysis reveals that the introduction of IDTR results in strong crystallinity, good miscibility, and proper vertical phase distribution, thereby realizing heightened and balanced charge transport behavior. Remarkably, the novel ternary OSCs have exhibited a significant enhancement in photovoltaic performance. Consequently, open-circuit voltage (V_OC ), short-circuit current (J_SC ), and fill factor (FF) have all witnessed substantial improvements with a remarkable power conversion efficiency (PCE) of 18.94% when L8-BO replaced Y6. Beyond the pronounced improvement in photovoltaic performance, superior device stability with a T₈₀ approaching 400 h is successfully achieved. This achievement is attributed to the synergistic interplay of IDTR, providing robust support for the overall enhancement of performance. These findings offer crucial guidance and reference for the design and development of efficient and stable OSCs.

The greatly reduced energy loss assisted by volatile solid additive 1,4-bis(iodomethyl)cyclohexane (DIMCH) is demonstrated, and the role of DIMCH in weakening the disparity of imbalanced crystallinity of donor and acceptor, and reducing the energy disorder and trap density is unveiled, and its function to achieve forefront power conversion efficiency of 18.8% for binary organic solar cells.

Abstract

The energy loss induced open-circuit voltage (V_OC) deficit hampers the rapid development of state-of-the-art organic solar cells (OSCs), therefore, it is extremely urgent to explore effective strategies to address this issue. Herein, a new volatile solid additive 1,4-bis(iodomethyl)cyclohexane (DIMCH) featured with concentrated electrostatic potential distribution is utilized to act as a morphology-directing guest to reduce energy loss in multiple state-of-art blend system, leading to one of highest efficiency (18.8%) at the forefront of reported binary OSCs. Volatile DIMCH decreases radiative/non-radiative recombination induced energy loss (ΔE ₂/ΔE ₃) by rationally balancing the crystallinity of donors and acceptors and realizing homogeneous network structure of crystal domain with reduced D–A phase separation during the film formation process and weakens energy disorder and trap density in OSCs. It is believed that this study brings not only a profound understanding of emerging volatile solid additives but also a new hope to further reduce energy loss and improve the performance of OSCs.

Herein, highly efficient mixed Sn-Pb PSCs are achieved by introducing multifunctional Tin (II) oxalate (SnC₂O₄). SnC₂O₄ with compensative Sn²⁺ and passivate defect, reduce Sn⁴⁺ and eliminate SnF₂ and PbI₂ residues. The device treats with SnC₂O₄ achieve a PCE of 21.43%. More importantly, chemically reductive C₂O₄ ^2- effectively suppresses the oxidation of Sn²⁺, leading to significant enhancement on stability.

Abstract

Tin-lead (Sn-Pb) mixed perovskite with a narrow bandgap is an ideal candidate for single-junction solar cells approaching the Shockley-Queisser limit. However, due to the easy oxidation of Sn²⁺, the efficiency and stability of Sn-Pb mixed perovskite solar cells (PSCs) still lag far behind that of Pb-based solar cells. Herein, highly efficient and stable FA_0.5MA_0.5Pb_0.5Sn_0.5I_0.47Br_0.03 compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnC₂O₄). SnC₂O₄ with compensative Sn²⁺ and reductive oxalate group C₂O₄ ²⁻ effectively passivates the cation and anion defects simultaneously, thereby leading to more n-type perovskite films. Benefitting from the energy level alignment and the suppression of bulk nonradiative recombination, the Sn-Pb mixed perovskite solar cell treated with SnC₂O₄ achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive C₂O₄ ²⁻ effectively suppresses the notorious oxidation of Sn²⁺, leading to significant enhancement in stability. Particularly, it dramatically improves light stability.

A reduction of the nonradiative recombination in polythiophene-based organic solar cells from the control of aggregation kinetics and orientation is achieved. By backbone design, PTTz-TzT with short drying time and face-on orientation exhibit reduced Urbach energy and nonradiative recombination in solar cells. PCEs higher than 16% in binary and 19% in ternary are achieved.

Abstract

In the pursuit of high-efficiency polythiophene (PT) organic solar cells (OSCs), a critical challenge is the reduction of nonradiative recombination. This study comprehensively explores polydithienylthiazolothiazole (PTTz)-based PT terpolymers: PTTz-Tz and PTTz-TzT, in which it is demonstrate that molecular structure alterations greatly influence the aggregation kinetics and orientation of these polymers. Specifically, PTTz-TzT achieves rapid ordering aggregation during spin coating, effectively suppressing excessive polymer aggregation and facilitating appropriate phase separation upon mixing with the acceptor. Meanwhile, PTTz-TzT inherently adopts a face-on orientation, resulting in more structured π–π stacking in the vertical direction after acceptor integration, compared to the intrinsic edge-on orientation of PTTz-Tz. These factors collectively contribute to lower Urbach energy and a substantial reduction of nonradiative recombination in PTTz-TzT-based OSCs, culminating in a high photovoltaic conversion efficiency (PCE) exceeding 16%. Furthermore, a prominent PCE of 19.11% is obtained by PTTz-TzT via ternary blend strategy, which is among the highest values reported for the OSCs. This investigation underscores the significance of aggregation kinetics and orientation in PT-based polymers, especially regarding Urbach energy and nonradiative recombination, and offers novel insights for designing high-performance polythiophene donors.

High-quality and additive-free α-FAPbI₃ films are successfully synthesized by the sustainable Alkane/Nanocrystals method, by employing FAPbI₃ nanocrystals input octane as antisolvent. But nanocrystal-surface capped ligands are found to aggregate and remain at the perovskite film surface. Surface treatment with PbAc isopropanol solution can effectively wash off the surplus surface ligands and modulate the surface chemistry.

Abstract

It's still a scientific issue to synthesize exotic amines-free and pure-phase FAPbI₃ film because most FAPbI₃ films are synthesized by adding MACl-like exotic amines salts in their precursor solution to reduce the phase transition barrier. In this work, high-quality and additive-free phase-pure α-FAPbI₃ films are successfully fabricated via the sustainable Alkane/Nanocrystals method. FAPbI₃ nanocrystals (NCs) are performed as the heterogeneous nuclei to promote the nucleation and crystallization of FAPbI₃ films. Cryogenic-TEM and in situ GIWAXS evidence the seed function and interesting phase evolution of FAPbI₃ NCs. The whole phase transition course of pure FAPbI₃ film is systematically studied. IR-AFM and ToF-SIMS reveal ligands capped on NCs are extruded to the film surface. PbAc-IPA solution treating the film surface can effectively wash off the surplus ligands at the surface and modulate the surface chemistry and energy levels. As a result, an average power conversion efficiency (PCE) of 21.45% is achieved for MA-free pure α-FAPbI₃ perovskite solar cells (PSCs), as well as the best light-soaking stability record of retaining 95% of the initial PCE after 800 h. This work paves a new way to fabricate MA-free pure α-FAPbI₃ PSCs.

A facile and eco-friendly dimethyl sulfoxide-mediated solution aging (DMSA) treatment is proposed to homogenize the morphology and composition of methylammonium-free wide-bandgap perovskite films, which contributes to highly efficient and stable semitransparent perovskite solar cells and tandem solar cells.

Abstract

A facile and eco-friendly dimethyl sulfoxide-mediated solution aging (DMSA) treatment is presented to control the crystallization dynamics of methylammonium (MA)-free wide-bandgap (WBG) perovskite films, enhancing film quality, and morphology for high-performance tandem solar cells. The comprehensive structural, morphological, and characterization analyses reveal that the DMSA treatment significantly enhances composition and morphology homogeneity while suppressing halide segregation. Consequently, opaque, and semi-transparent MA-free WBG perovskite solar cells (PSCs) exhibit remarkable power conversion efficiencies (PCEs) of 18.28% and 17.61%, respectively. Notably, the unencapsulated DMSA-treated devices maintain 95% of the initial PCE after 900 h of continuous operation at 55 °C ± 5 °C. Furthermore, stacking semi-transparent DMSA-treated PSCs as top cells in a 4T tandem configuration, along with silicon heterojunction (SHJ), lead–tin (Pb–Sn) alloyed PSCs, and organic photovoltaics (OPV) as bottom cells, yields impressive PCEs of 28.09%, 26.09%, and 25.28%, respectively, for the fabricated tandem cells. This innovative approach opens new avenues for enhancing the photo-stability and photovoltaic performance of perovskite-based tandem solar cells.

Self-assembled monolayer (SAM) molecules are extensively employed in perovskite solar cells, serving both as charge transport materials and interfacial modulators. These molecules play a crucial role in adjusting surface energy levels, reducing interfacial trap defects, and enhancing perovskite crystallization quality, thereby leading to improved performance and stability of perovskite solar cells.

Abstract

Perovskite solar cells (PSCs) hold significant promise as the next-generation materials in photovoltaic markets, owing to their ability to achieve impressive power conversion efficiencies, streamlined fabrication processes, cost-effective manufacturing, and numerous other advantages. The utilization of self-assembled monolayer (SAM) molecules has proven to be a significant success in enhancing device efficiency and extending device stability. This review highlights the dual use of SAM molecules in the realm of PSCs, which can not only serve as charge transport materials but also act as interfacial modulators. These research endeavors encompass a wide range of applications for various SAM molecules in both n-i-p and p-i-n structured PSCs, providing a deep insight into the underlying mechanisms. Furthermore, this review proposes current research challenges for future investigations into SAM materials. This timely and thorough review seeks to provide direction and inspiration for current research efforts dedicated to the ongoing incorporation of SAMs in the field of perovskite photovoltaics.

Publication date: August 2024

Source: Journal of Energy Chemistry, Volume 95

Author(s): Shuhang Bian, Yuqi Wang, Fancong Zeng, Zhongqi Liu, Bin Liu, Yanjie Wu, Long Shao, Yongzhi Shao, Huan Zhang, Shuainan Liu, Jin Liang, Xue Bai, Lin Xu, Donglei Zhou, Biao Dong, Hongwei Song

In this study, to overcome the wettability issue of highly hydrophobic self-assembled monolayer (SAM), a new SAM deposition method based on a vacuum-assisted deposition (VD) process was attempted. The VD process improved the performance of PSCs by improving the wettability of the hydrophobic SAM layer. This finding can provide a cornerstone for using highly hydrophobic SAM-based hole transport layer.

Recently, various carbazole-based self-assembled monolayers (SAMs) have been investigated for use in the hole transport layer (HTL) of perovskite solar cells (PSCs). In particular, [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) is attracting attention as an HTL for high-efficiency PSC due to its potential for high open-circuit voltage (V _OC) and fill factor (FF). However, Me-4PACz has strong hydrophobicity due to its methyl group (–CH₃) and long alkyl chain (C4H₈), which makes it difficult to deposit a high-quality perovskite layer on top of conventionally coated Me-4PACz. In this study, to overcome these limitations, a new SAM deposition method based on a vacuum-assisted deposition (VD) process is attempted. As a result, a uniform perovskite layer is deposited on top of Me-4PACz through a very simple VD process, achieving 20.31% efficiency, which is not only close to the highest efficiency among Me-4PACz-based PSCs, but also improved long-term stability of the device. It is believed that the findings of this study can be a cornerstone for using SAM-based HTL with high hydrophobicity in the future.

The study reports the synthesis of the first crystalline 2D fullerene-based metal halide semiconductor, namely (C₆₀-2NH₃)Pb₂I₆. Utilization of the C₆₀-2NH₃I₂ adduct as an interfacial layer in mixed Pb-Sn perovskite solar cells substantially improved both carrier transport and device stability. This work sets the foundation for the development of a new family of multifunctional materials, namely Fullerene Metal Halide Semiconductors.

Abstract

Despite advances in mixed tin-lead (Sn-Pb) perovskite-based solar cells, achieving both high-efficiency and long-term device stability remains a major challenge. Current device deficiencies stem partly from inefficient carrier transport, originating from defects and improper band energy alignment among the device's interfaces. Developing multifunctional interlayer materials simultaneously addressing the above concerns poses an excellent strategy. Herein, through molecular and crystal engineering, an amine-functionalized C₆₀ mono-adduct derivative (C₆₀-2NH₃ = bis(2-aminoethyl) malonate-C₆₀) is utilized for the synthesis of the first crystalline fullerene-based 2D metal halide semiconductor, namely (C₆₀-2NH₃)Pb₂I₆. Single crystal XRD studies elucidated the structure of the new material, while DFT calculations highlighted the strong contribution of C₆₀-2NH₃ to the electronic density of states of the conduction band of (C₆₀-2NH₃)Pb₂I₆. Utilization of C₆₀-2NH₃ as an interlayer between a FA_0.6MA_0.4Pb_0.7Sn_0.3I₃ perovskite and a C₆₀ layer offered superior band energy alignment, reduced nonradiative recombination, and enhanced carrier mobility. The corresponding perovskite solar cell (PSC) device achieved a power conversion efficiency (PCE) value of 21.64%, maintaining 90% of its initial efficiency, after being stored under a N₂ atmosphere for 2400 h. This work sets the foundation for developing a new family of functional materials, namely Fullerene Metal Halide Semiconductors, targeting applications from photovoltaics to catalysis, transistors, and supercapacitors.

A versatile SnO₂ modifier, namely tea saponin (TS), has been demonstrated to significantly enhance carrier extraction capabilities and aid in the optimal growth of perovskite on the (111) facet. As a corollary, the perovskite solar cell based on TS-modified SnO₂ exhibits a notable improvement in V _oc and FF, ultimately achieving a superior PCE of 24.2% with improved storage stability.

Abstract

Different facets in perovskite crystals exhibit distinct atomic arrangements, influencing their electronic, physical, and chemical properties. Perovskite films incorporating tin oxide (SnO₂) as the electron transport layer face challenges in facet regulation. This study reveals that tea saponin (TS), a natural compound serves as a SnO₂ modifier, facilitates optimal growth of perovskite crystals on the (111) facet. The modification promotes preferential crystal orientation through hydrogen bond and Lewis coordination. TS forms a chelate with SnO₂, resulting in a smoother film and n-type doping, leading to improved carrier extraction and reduced defects. The TS-modified perovskite solar cells achieve a champion efficiency of 24.2%, leveraging from an obvious enhancement of open-circuit voltage (V _oc) of 1.18 V and fill factor (FF) of 82.8%. The devices also demonstrate enhanced humidity tolerance and storage stability, ensuring improved stability without encapsulation.

Nature Energy, Published online: 17 April 2024; doi:10.1038/s41560-024-01500-2