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The Sn-Pb alloyed perovskite films with stable α -phase and oxidation resistance are prepared by bulk doping (CsCl) and surface coordination (PbSO₄). The less oxidation of Sn²⁺ and enhanced stability are caused by reconfiguring perovskite crystallization and the formed dense water-insoluble hydrophobic surface. The ultimately fabricated perovskite solar cells deliver a champion power conversion efficiency of 10.39% and excellent stability.

Abstract

Novel all-inorganic Sn-Pb alloyed perovskites are developed aiming for low toxicity, low bandgap, and long-term stability. Among them, CsPb_{1− x} Sn _x I₂Br is predicted as an ideal perovskite with favorable band gap, but previously is demonstrated unable to convert to perovskite phase by thermal annealing. In this report, a series of CsPb_{1− x} Sn _x I₂Br perovskites with tunable bandgaps from 1.92 to 1.38 eV are successfully prepared for the first time via low annealing temperature (60 °C). Compared to the pure CsPbI₂Br, these Sn-Pb alloyed perovskites show superior stability. Furthermore, a novel α-phase-stabilization mechanism of the inorganic Sn-Pb alloyed perovskite by reconfiguring the perovskite crystallization process with chloride doping is provided. Simultaneously, a dense protection layer is formed by the coordination reaction between the surface lead dangling bonds and sulfate ion to retard the permeation of external oxygen and moisture, leading to less oxidation of Sn²⁺ in perovskite film. As a result, the fabricated all-inorganic Sn-Pb perovskite solar cells (PSCs) show a champion power conversion efficiency of 10.39% with improved phase stability and long-term ambient stability against light, heat, and humidity. This work provides a viable strategy in fabricating high-performance narrow-bandgap all-inorganic PSCs.

Annealing-free solution-processable NiO is developed and applied in inverted polymer solar cells based on non-fullerene system PTB7-Th:IEICO-4F. The inverted solar cells with annealing-free NiO exhibit equivalence efficiency and better stability without high-temperature annealing compared to the solar cells with the MoO _x hole transport layer fabricated by thermal evaporation.

Abstract

Nickel oxide (NiO) offers intrinsic p-type behavior and high thermal and chemical stability, making it promising as a hole transport layer (HTL) material in inverted organic solar cells. However, its use in this application has been rare because of a wettability problem caused by use of water as base solvent and high-temperature annealing requirements. In the present work, an annealing-free solution-processable method for NiO deposition is developed and applied in both conventional and inverted non-fullerene polymer solar cells. To overcome the wettability problem, the typical DI water solvent is replaced with a mixed solvent of DI water and isopropyl alcohol with a small amount of 2-butanol additive. This allows a NiO nanoparticle suspension (s-NiO) to be deposited on a hydrophobic active layer surface. An inverted non-fullerene solar cell based on a blend of p-type polymer PTB7-Th and non-fullerene acceptor IEICO-4F exhibits the high efficiency of 11.23% with an s-NiO HTL, comparable to the efficiency of an inverted solar cell with a MoO _x HTL deposited by thermal evaporation. Conventionally structured devices including this s-NiO layer show efficiency comparable to that of a conventional device with a PEDOT:PSS HTL.

Flexible perovskite solar cells deliver a 21.1% power conversion efficiency (certified 20.5%) with good bending resistance and long-term stability via creating a dual-functional 2D perovskite layer at the interface.

Abstract

Flexible perovskite solar cells (f-PSCs) have been attracting tremendous attention due to their potentially commercial prospects in flexible energy system and mobile energy system. Reducing the energy barriers and charge extraction losses at the interfaces between perovskite and charge transport layers is essential to improve both efficiency and stability of f-PSCs. Herein, 4-trifluoromethylphenylethylamine iodide (CF₃PEAI) is introduced to form a 2D perovskite at the interface between perovskite and hole transport layer (HTL). It is found that the 2D perovskite plays a dual-functional role in aligning energy band between perovskite and HTL and passivating the traps in the 3D perovskite, thus reducing energy loss and charge carrier recombination at the interface, facilitating the hole transfer from perovskite to the Spiro-OMeTAD. Consequently, the photovoltaic performance of f-PSCs is significantly improved, leading to a power conversion efficiency (PCE) of 21.1% and a certified PCE of 20.5%. Furthermore, the long-term stability of f-PSCs is greatly improved through the protection of 2D perovskite layer to the underlying 3D perovskite. This work provides an excellent strategy to produce efficient and stable f-PSCs, which will accelerate their potential applications.

Si nanowires are modified with tetramethylammonium hydroxide and the (PEDOT:PSS) solution is doped with 3-glycidoxypropyltrimethoxysilane to improve the contact quality of the heterojunction. As a result, the power conversion efficiency of organic/nanostructured Si heterojunction solar cells can reach more than 15%, with a record V _OC of 660 mV.

Nanostructured Si has attracted widespread attention due to its strong light-harvesting ability, which is beneficial to improve the performance of solar cells. However, the poor contact of the organic/nanostructured Si interface and the large number of recombination centers on the Si surface result in an unsatisfactory open circuit voltage (V _OC) and fill factor (FF) of the device. Herein, a simple and versatile method, Si nanowires modified with tetramethylammonium hydroxide (TMAH) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) doped with 3-glycidoxypropyltrimethoxydsilane (GOPS), is proposed to improve the contact quality of the heterojunction. TMAH treatment adjusts the morphology of the Si nanowires and makes the surface smoother, effectively inhibiting surface recombination at the heterojunction interface. Moreover, the GOPS-doped PEDOT:PSS solution can achieve conformal contact on the surface of nanostructured Si, which is more conducive to the extraction and separation of charges. As a result, a record V _OC of 660 mV is obtained for PEDOT:PSS/nanostructured Si hybrid solar cells. In addition, the short circuit current density (J _SC) is as high as 33.00 mA cm⁻², and the FF is as high as 69.03%; therefore, the efficiency of the device reaches 15.01%. The results provide a simple and feasible strategy to improve the junction quality and performance of organic/Si solar cells.

Herein, perovskite defects are categorized into two big groups of halide and cation vacancies. The defect passivation methods are divided into bulk and surface treatment of perovskite films. All kinds of passivating agent materials are classified based on their functional groups for defect passivation. Finally, a comprehensive perspective for achieving high-performance and stable perovskite solar cells is provided.

Perovskite solar cells (PSCs) have been introduced as an attractive photovoltaic technology over the past decade due to their low-cost processing, earth-abundant raw materials, and high power conversion efficiencies (PCEs) of up to 25.2%. However, the relatively high density of defects within the bulk, grain boundaries, and surface of polycrystalline perovskite films acts as recombination centers and facilitates ion migration, lowering the theoretical PCE ceiling, often leading to inferior device stability. Therefore, understanding the defect sources and developing passivation methods are key factors for reaching higher PCEs and stabilities in perovskite photovoltaics. Herein, various passivation methods, including bulk and surface treatment of perovskite films, are explored. In the bulk treatment, the passivating agents should be directly added to the perovskite precursor. However, in the surface treatment method, the surface of perovskite films can be treated by inducing passivating agents during the intermediate phase or after annealing steps, denoted here as in-film or surface posttreatment. In addition, different kinds of passivating agents are categorized based on their functional groups. Finally, the outline directions to minimize the defects in perovskite films are highlighted.

This article introduces a bottom layer modifier for ZnO-based methylammonium (MA)-free perovskite solar cells. Chlorine-containing phenanthroline derivative (Cl-phen) reduces the surface oxygen defects, improves the charge extraction efficiency, and moderately increases the hydrophobicity to achieve a large grain size. A high-performance solar cell with 21.15% is achieved. Its unencapsulated device maintains 91.5% of its stating PCE after 1500 h.

Formamidinium cesium (FACs) perovskite solar cells (PSCs) with the exclusion of methylammonium (MA) cations often have greatly improved device stability; however, their inferior performance compared with MA-based devices has impeded the real application. Among various device engineering strategies, bottom interfacial engineering is a promising method to simultaneously achieve the passivation of interfacial defects and the crystallization control of perovskite. Herein, a simple and effective bottom interfacial design is presented to improve the efficiency and stability of FACs PSCs by capping o-phenanthroline derivatives on the ZnO electron transporting layer (ETL). The most efficient modifier, 4,7-Dichloro-1,10-phenanthroline (Cl-phen), can improve the crystallinity of the perovskite film by chlorinated surface and passivate the defects of ZnO by reducing surface hydroxyl groups and oxygen vacancies. In addition, Cl-phen modified ZnO shows better energy alignment with FACs perovskite and increases the built-in electric field cascade by 80 mV. As a result, a champion device efficiency of 21.15% is obtained using ZnO/Cl-phen bilayer ETL. The stability has also been improved using ZnO/Cl-phen bilayer ETL, in which 91.5% of initial PCE is retained after 1500 h of storage at ambient environment (RH: 40–50%) without encapsulation.

Herein, a unique triple-ion migration phenomenon in Ag₃BiI₆ solar cells is reported. Under ambient atmosphere, Ag⁺, Bi³⁺, and I⁻ ions migrate and decompose the metal electrode leading to performance degradation. This study highlights the importance of understanding the Ag₃BiI₆ material for better solar cell design and also stimulates the use of this unique ion-migration behavior in other optoelectronics.

Silver bismuth iodide (SBI) materials have recently gained attention as nontoxic alternatives to lead perovskites. Although most of the studies have been focusing on photovoltaic performance, the inherent ionic nature of SBI materials, their diffusive behavior, and influence on material/device stability is underexplored. Herein, AgBi₂I₇, Ag₂BiI₅, and Ag₃BiI₆ thin films are developed in controlled ambient humidity conditions with a decent efficiency up to 2.32%. While exploring the device stability, it is found that Ag₃BiI₆ exhibits a unique ion-migration behavior where Ag⁺, Bi³⁺, and I⁻ ions migrate and diffuse through the dopant-free hole transport layer (HTL) leading to degradation. Interestingly, this ion-migration behavior is relatively fast for the case of antisolvent-processed Ag₃BiI₆ thin-film-based devices contrasting the case of without antisolvent and is not observed for other SBI material-based devices. Theoretical calculations suggest that low decomposition enthalpy favors the decomposition of Ag₃BiI₆ to AgI and BiI₃ causing migration of ions to the electrode which is protected by using a thick HTL . The new mechanism reported herein underlines the importance of SBI material composition and fundamental mechanism understanding on the stability of Ag₃BiI₆ material for better solar cell design and also in extending the applications of unique ion-migration behavior in various optoelectronics.

SiNcTI-Br with strong self-doping property, high conductivity, and high electron mobility is an excellent cathode interlayer material. The interlayer boosts the power conversion efficiency of PM6:Y6-based OSCs to 16.71 %. It is the first naphthalocyanine derivative used as interlayer material in optoelectronic devices.

Abstract

Naphthalocyanine derivatives (SiNcTI-N and SiNcTI-Br) were firstly used as excellent cathode interlayer materials (CIMs) in organic solar cells, via introducing four electron-withdrawing imide groups and two hydrophilic alkyls. Both of them showed deep LUMO energy levels (below −3.90 eV), good thermal stability (T_d >210 °C), and strong self-doping property. The SiNcTI-Br CIM displayed high conductivity (4.5×10⁻⁵ S cm⁻¹) and electron mobility (7.81×10⁻⁵ cm² V⁻¹ s⁻¹), which could boost the efficiencies of the PM6:Y6-based OSCs over a wide range of CIM layer thicknesses (4–25 nm), with maximum efficiency of 16.71 %.

Laser technologies will play an essential role in the industrialization of perovskite solar cells, both to achieve high active surface area modules and for the deposition and treatment of the critical layers. The speed of laser processing for the interconnects P1, P2, and P3 and protecting the perovskite module from exposure to the atmosphere using a quartz frame is shown.

Abstract

The perovskite photovoltaic technology is now transitioning from basic research to the pre-industrialization phase. In order to achieve reliable and high-performance commercial perovskite solar modules, high throughput manufacturing technologies must now be adapted to the specific constraints and requirements imposed by the perovskite solar cells unique new chemistries, film deposition methodologies, and encapsulation requirements. Laser technologies will play an important role in the industrialization of these devices, both to achieve high active surface area modules and for the deposition and/or treatment of the critical layers. Industrial lasers will be essential to achieve active areas greater than 95% of the total area to retain the benefits of the very high performances reported for <1 cm² laboratory cells. The speed of laser processing for the preparation of interconnects is unrivalled by comparison to other structuring methods. Recent reports of the use of lasers in upscaling perovskite solar cells are presented and analyzed here.

Fluoroethylamine passivates defects in perovskite films as a result of F distribution throughout the bulk and even at the surface. The nonradiative recombination in perovskite films using derivatives of this compound is suppressed, the carrier-lifetime is prolonged, and the film–air interface offers greater hydrophobicity. The corresponding solar cells deliver high efficiency of up to 23.40%. The unencapsulated device shows good environmental stability, maintaining 87% of its initial efficiency after exposure to the ambient environment for 1200 h.

Abstract

Defects in perovskite layers usually cause nonradiative recombination, impairing device performance and stability. Here, fluoroethylamine (FC₂H₄NH₃, FEA) is integrated into the perovskite film to passivate defects. By engineering of different amounts of fluorine in the molecule, it is found that when 2-fluoroethylamine (1FEA), in which one F bonds to the first carbon atom at the end of the molecule's structure, is used, the F atoms appear to be distributed throughout the bulk to the very surface. When 2,2-difluoroethylamine (2FEA) and 2, 2, 2-trifluoroethylamine (3FEA) are used, F is prone to distribution in the bulk of the perovskite film, while there appears to be no detectable F content on the surface. With the FEA passivation, the nonradiative recombination is suppressed, the carrier-lifetime is improved to 840.01 ns, and the film-air interface offers greater hydrophobicity, especially in the case of 1FEA, where because it is distributed throughout the film thickness, it passivates more defects and delivers the highest efficiency, as much as 23.40%. The device with 3FEA shows the best environmental stability; specifically, the bare cell without any encapsulation maintains 87% of its initial efficiency after exposure to the ambient environment for 1200 h.

Charge dynamics and energy loss (E _loss) in ternary organic solar cell (OSCs) with an impressive fill factor (FF) of 80.88% are thoroughly investigated by transient characterization techniques, which is expect to aid development of high-FF and low-E _loss ternary OSCs.

Abstract

Ternary architecture is a promising strategy to enhance power conversion efficiencies (PCEs) of organic solar cells (OSCs). However, among all the photovoltaic parameters that govern the final PCEs, the fill factor (FF) for ternary OSCs is generally below 78%, limiting solar cells’ performance. Here, charge dynamics in the ternary cells PM6:DRTB-T-C4:Y6 with a FF of 80.88% and a PCE of 17.05% are thoroughly investigated by a series of transient characterization technologies, including transient absorption spectroscopy, transient photovoltage, and transient photocurrent measurements. The impressive FF results from effective exciton dissociation, enhanced charge transport and suppressed recombination in ternary cells. Moreover, the correlation between the measured FF and the charge recombination-extraction competition is quantitatively analyzed by using a circuit model. The ternary cells also show small energy loss (E _loss). The findings here provide insight into achieving high-FF and low-E _loss ternary OSCs.

Samarium doping nickel oxide (Sm:NiO _x ) reduces the formation energy of Ni vacancies and increases hole density. Thus, both electronic conductivity and work function are enlarged, favoring the extraction of holes and suppression of charge recombination. Eventually, Sm:NiO _x -based flexible and rigid inverted perovskite solar cells attain efficiencies of 17.95% and 20.71%, respectively. Importantly, it delivers high efficiency of 15.27% on a 40 × 40 mm² module.

Abstract

Hole transport layers (HTLs) play a key role in perovskite solar cells (PSCs), particularly in the inverted PSCs (IPSCs) that demand more in its stability. In this study, samarium-doped nickel oxide (Sm:NiO _x ) nanoparticles are synthesized via a chemical precipitation method and deposited as a hole transport layer in the IPSCs. Sm³⁺ doping can reduce the formation energy of Ni vacancy and naturally increase the density of Ni vacancies, thereby rendering increased hole density. Thenceforth, the electronic conductivity is enhanced significantly, and work function enlarged in the Sm:NiO _x film in favor of extracting holes and suppressing charge recombination. Consequently, the Sm:NiO _x -based IPSCs attain outstanding power conversion efficiencies as high as 20.71%. Even when it is applied in flexible solar cells, it still outputs efficiency as high as 17.95%. More importantly, the Sm:NiO _x is compatible with large-scale processing whereby the large area IPSCs of 1.0 cm² and 40 × 40 mm² deliver high efficiencies of 18.51% and 15.27%, respectively, all are among the highest for the inorganic HTLs based IPSCs. This research demonstrates that, while revealing the doping effect in depth, Sm:NiO _x can be a promising hole transport material for fabricating efficient, large-area, and flexible IPSCs in the future.

In the PM6:Y6 blend, the strong intermolecular interaction and the formation of the delocalized excited state in acceptor Y6 are favorable for rapid exciton migration and hole transfer at donor/acceptor interfaces, thus resulting in a considerably high hole transfer efficiency of 71.4%. While the transfer efficiency only reaches 13.1% in PM6:3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC) blend, due to the weak intermolecular π–π interaction in the ITIC component.

Abstract

Organic solar cells (OSCs) based on small molecular acceptors (SMAs) have made great development with a power conversion efficiency (PCE) over 16% due to the design of novel materials and advances in device preparation technology. This work fabricates two bulk-heterojunction photovoltaic devices containing the same wide-bandgap donor PM6, respectively, matched with popular Y6 and ITIC SMAs. The PM6:Y6-based device achieves a much higher PCE of 15.21% than the PM6:ITIC-based device of 9.02%. On the basis of comparisons of macroscopic performances in the quasistatic regime, transient absorption spectroscopy (TAS) is further performed to better understand the microscopic dynamics difference in charge separation processes between the two photovoltaic blends. According to the TAS results, the calculated hole transfer efficiency in PM6:Y6 is 71.4%, far greater than the efficiency of 13.1% in PM6:ITIC, demonstrating favorable charge separation at donor/acceptor interfaces via hole transfer channel in PM6:Y6. The favorable hole transfer in PM6:Y6 is accounted for by its better mutual miscibility between the donor and acceptor, and the formation of long-lived delocalized intramoiety excimer state in the acceptor. These results highlight the important role of proper molecular design strategy with strong intermolecular coupling and beneficial film morphology on facilitating charge generation in OSCs adopting SMAs.

Copolymer series with varying contents of triisopropylsilyl-substituted benzo[1,2-b:4,5-c′]dithiophene-4,8-dione are synthesized and characterized. Using them as donors for bulk-heterojunction organic solar cells, a high power conversion efficiency of 17.01% is achieved from optimal composition of monomers with balanced charge transport, enhanced charge generation/dissociation kinetics, and minimized total energy and recombination losses.

Abstract

Considering the special functions of fused-ring aromatic building blocks and Si-atom in high-performance donor–acceptor-conjugated materials at the same time, herein the synthesis of a novel fused-ring tricyclic heterocycle, triisopropylsilyl-substituted benzo[1,2-b:4,5-c′]dithiophene-4,8-dione (iBDD-Si), an isomer of well-known benzo[1,2-c:4,5-c′]dithiophene-4,8-dione is presented. The iBDD-Si-based copolymer series (PM6, PM6-5Si, PM6-10Si, and PM6-15Si) is synthesized via Stille polymerization, revealing fine-tuned optical and electrochemical properties, and molecular packing with varying iBDD-Si contents in the backbone. Organic solar cells are fabricated by pairing the copolymer donors with nonfullerene acceptor N3 and characterized. High power conversion efficiency of more than 17% is achieved using the PM6-5Si-based solar cell, which is attributed to the balanced charge transport, enhanced charge generation/dissociation kinetics, and minimized total energy and recombination losses. It is demonstrated that iBDD-Si is a promising backbone toolbox for various high-performance conjugated materials.

Molecular hole-transporting materials with different anchoring groups are synthesized. The anchoring groups with a stronger bonding strength enable greatly enhanced compactness of self-assembly monolayer, which benefits hole-extraction and electron-blocking in complete devices. When applied in inverted perovskite solar cells, 1 cm² devices show a promising power conversion efficiency of over 20% with high stability.

Abstract

Anchoring-based self-assembly (ASA) has emerged as a material-saving and highly scalable strategy to fabricate charge-transporting monolayers for perovskite solar cells (PSCs). However, the interfacial hole-extraction and electron-blocking performances are highly dependent on the compactness of the ASA monolayers, which has been largely ignored though it is very crucial to the efficiency and stability of PSCs. Here, strategically designed hole-transporting molecules with different anchoring groups are incorporated to investigate the effect of bonding strength on monolayer quality and correlate these with the performance of p-i-n structured PSCs. It is unraveled that the anchoring groups with a stronger bonding strength are advantageous for improving the assembly rate, density, and compactness of ASA monolayer, thus enhancing charge collection and suppressing interfacial recombination. The prototypical PSCs based on optimal ASA monolayer achieve a high power conversion efficiency (PCE) of 21.43% (0.09 cm²). More encouragingly, when enlarging the device area by tenfold, a comparable PCE of 20.09% (1.0 cm²) can be obtained, suggesting that the ASA strategy is practically useful for scaling-up. The robust anchoring of the ASA monolayer also enhances devices stability, retaining 90% of initial PCE after three months. This study provides important insights into the ASA charge-transporting monolayers for efficient and stable PSCs.

This study develops a universal bottom interface modification method with diverse 2D spacers, which significantly enhance the device performance of inverted perovskite solar cells from 20.7% to 21.6%. The lift-off method is used to directly study the change of optoelectronic properties at the bottom interface and unveils the formation of 2D/3D heterojunction as the general mechanism underlying the device performance enhancement.

Abstract

Although the 2D spacer modification is widely studied in perovskite solar cells (PVSCs), the energy level alignment between the 2D/3D interfaces makes it unfavorable for top surface passivation in the inverted p-i-n device structure. To address this issue, the effect of bottom interface modification is studied with three representative 2D spacers, i.e., the Ruddlesden-Popper 2D spacer, Dion-Jacobson 2D spacer, and strong passivation 2D spacer, in inverted p-i-n PVSCs. After optimization, the PVSCs with these 2D spacer modifications universally exhibit the best efficiencies of ≈21.6%, which constitutes dramatic improvement compared to the control device (20.7%). By lifting off the perovskite layer, the optoelectronic properties of the bottom surface are studied, and the mechanism underlying the improved device performance is unveiled to be uniformly originated from the formation of 2D/3D heterojunction, where the cascade valence band facilitates the hole collection and electron back scattering field suppresses the charge recombination at the anode interface. Besides, the unencapsulated device retains 90% of initial efficiency after 30 days of storage in ambient air with a relative humidity of 30 ± 5%, indicating excellent stability against moisture and oxygen. This study provides insight into the bottom interface modification with diverse 2D spacers for high-performance p-i-n structured PVSC devices.

Four emerging perovskite structures that have origins in pre-existing technologies such as silicon and chalcogenide-based photovoltaic cells are reviewed. The implementation of the new architectures holds great promise in reducing transport losses, light management, and stability. To guide further research into these areas key design criteria are identified and key characterization methods discussed.

Abstract

Over the past decade, perovskite solar cells (PSCs) have quickly established themselves as a promising technology boasting both high efficiency and low processing costs. The rapid development and success of PSCs is a product of substantial research effort addressing compositional engineering, thin film fabrication, surface passivation, and interfacial treatments. Recently, engineering of device architecture has entered a renaissance with the emergence of several new bulk and graded heterojunction structures. These structures promote a lateral approach to the development of single-junction PSCs affording new opportunities in light management, defect passivation, carrier extraction, and long-term stability. Following a short overview of the historic evolution of PSC architectures, a detailed discussion of the promising progress of the recently reported perovskite bulk heterojunction and graded heterojunction approaches are offered. To enable better understanding of these novel architectures, a range of approaches to characterizing the architectures are presented. Finally, an outlook and perspective are provided offering insights into the future development of PSC architecture engineering.

An intrinsically stretchable organic solar cell (OSC) with an efficiency of over 10% is achieved by the transfer printing method. The ductility of bulk heterojunction film is greatly improved to 20% by introducing polydimethylsiloxane additives, and intimated multilayer stacking is realized with the assistance of electrical adhesive D-Sorbitol. The stretchable OSC exhibits ultra-flexibility and superior stretchability without sacrificing the device performance.

Abstract

Stretchable organic solar cells (OSCs) simultaneously possessing high-efficiency and robust mechanical properties are ideal power generators for the emerging wearable and portable electronics. Herein, after incorporating a low amount of trimethylsiloxy terminated polydimethylsiloxane (PDMS) additive, the intrinsic stretchability of PTB7-Th:IEICO-4F bulk heterojunction (BHJ) film is greatly improved from 5% to 20% strain without sacrificing the photovoltaic performance. The intimate multi-layers stacking of OSCs is also realized with the transfer printing method assisted by electrical adhesive “glue” D-Sorbitol. The resultant devices with 84% electrode transmittance exhibit a remarkable power conversion efficiency (PCE) of 10.1%, which is among the highest efficiency for intrinsically stretchable OSCs to date. The stretchable OSCs also demonstrate the ultra-flexibility, stretchability, and mechanical robustness, which keep the PCE almost unchanged at small bending radium of 2 mm for 300 times bending cycles and retain 86.7% PCE under tensile strain as large as 20% for the devices with 70% electrode transmittance. The results provide a universal method to fabricate highly efficient intrinsically stretchable OSCs.

Two configurational controlled polymers are reported here. The γ-position based polymer exhibits good solubility, broadened UV absorption, and enhanced charge mobility, while the δ-position based polymer shows excessive aggregation and is difficult to process in solution. When blended with PM6, PBTIC-γ-2F2T achieves excellent device performance with a PCE of 14.32%, but the PBTIC-δ-2F2T delivers a PCE of almost zero (0.02%).

Abstract

The design of polymer acceptors plays an essential role in the performance of all-polymer solar cells. Recently, the strategy of polymerized small molecules has achieved great success, but most polymers are synthesized from the mixed monomers, which seriously affects batch-to-batch reproducibility. Here, a method to separate γ-Br-IC or δ-Br-IC in gram scale and apply the strategy of monomer configurational control in which two isomeric polymeric acceptors (PBTIC-γ-2F2T and PBTIC-δ-2F2T) are produced is reported. As a comparison, PBTIC-m-2F2T from the mixed monomers is also synthesized. The γ-position based polymer (PBTIC-γ-2F2T) shows good solubility and achieves the best power conversion efficiency of 14.34% with a high open-circuit voltage of 0.95 V when blended with PM6, which is among the highest values recorded to date, while the δ-position based isomer (PBTIC-δ-2F2T) is insoluble and cannot be processed after parallel polymerization. The mixed-isomers based polymer, PBTIC-m-2F2T, shows better processing capability but has a low efficiency of 3.26%. Further investigation shows that precise control of configuration helps to improve the regularity of the polymer chain and reduce the π–π stacking distance. These results demonstrate that the configurational control affords a promising strategy to achieve high-performance polymer acceptors.

In article number 2009246, Jung Hwa Seo, Bright Walker, and co-workers demonstrate that a simple Cu(II) polyelectrolyte is able to create effective p-type junctions in perovskite solar cells by creating an interfacial dipole which effectively alters the energy band structure to extract positively charged holes. This innovation is used to greatly improve the performance of methylammonium lead iodide perovskite solar cells.

Here, the effect of Al-CuS is investigated as the hole-transport layer (HTL) for perovskite solar cells. It is shown that the sulfur in the HTL can interact with the perovskite film and lead to the better interface crystallization of perovskite. Due to this improved interface quality, sulfide-HTL-based devices outperform the oxide-HTL-based devices in terms of stability.

Abstract

Inorganic hole-transport layers (HTLs) are widely investigated in perovskite solar cells (PSCs) due to their superior stability compared to the organic HTLs. However, in p–i–n architecture when these inorganic HTLs are deposited before the perovskite, it forms a suboptimal interface quality for the crystallization of perovskite, which reduces device stability, causes recombination, and limits the power conversion efficiency of the device. The incorporation of an appropriate functional group such as sulfur-terminated surface on the HTL can enhance the interface quality due to its interaction with perovskite during the crystallization process. In this work, a bifunctional Al-doped CuS film is wet-deposited as HTL in p–i–n architecture PSC, which besides acting as an HTL also improves the crystallization of perovskite at the interface. Urbach energy and light intensity versus open-circuit voltage characterization suggest the formation of a better-quality interface in the sulfide HTL–perovskite heterojunction. The degradation behavior of the sulfide-HTL-based perovskite devices is studied, where it can be observed that after 2 weeks of storage in a controlled environment, the devices retain close to 95% of their initial efficiency.

Perovskite solar cells (PSCs) are fabricated using a novel organic cation (TTMAI) treatment on a 3D perovskite, which enables higher power conversion efficiency (PCE) and improves stability. The PCE enhancement is explained by the drift-diffusion modeling. In addition, TTMAI-treated 3D perovskite-based semitransparent PSCs are also realized, and a notable increase in PCE and stability is obtained.

Abstract

Perovskite surface treatment with additives has been reported to improve charge extraction, stability, and/or surface passivation. In this study, treatment of a 3D perovskite ((FAPbI₃)_{1− x} (MAPbBr₃) _x ) layer with a thienothiophene-based organic cation (TTMAI), synthesized in this work, is investigated. Detailed analyses reveal that a 2D (n = 1) or quasi-2D layer does not form on the PbI₂-rich surface 3D perovskite. TTMAI-treated 3D perovskite solar cells (PSCs) fabricated in this study show improved fill factors, providing an increase in their power conversion efficiencies (PCEs) from 17% to over 20%. It is demonstrated that the enhancement is due to better hole extraction by drift-diffusion simulations. Furthermore, thanks to the hydrophobic nature of the TTMAI, PSC maintains 82% of its initial PCE under 15% humidity for over 380 h (the reference retains 38%). Additionally, semitransparent cells are demonstrated reaching 17.9% PCE with treated 3D perovskite, which is one of the highest reported efficiencies for double cationic 3D perovskites. Moreover, the semitransparent 3D PSC (TTMAI-treated) maintains 87% of its initial efficiency for six weeks (>1000 h) when kept in the dark at room temperature. These results clearly show that this study fills a critical void in perovskite research where highly efficient and stable semitransparent perovskite solar cells are scarce.

A universal morphology optimization method is developed by applying anthracene as a solid additive to improve the photovoltaic performance of polymer solar cells. Anthracene can restrict the over-aggregation of nonfullerene acceptors during the film-forming process, and then facilitate bicontinuous phase separation during the kinetic process of its removal in the blend under thermal annealing.

Abstract

Currently, morphology optimization methods for the fused-ring nonfullerene acceptor-based polymer solar cells (PSCs) empirically follow the treatments originally developed in fullerene-based systems, being unable to meet the diverse molecular structures and strong crystallinity of the nonfullerene acceptors. Herein, a new and universal morphology controlling method is developed by applying volatilizable anthracene as solid additive. The strong crystallinity of anthracene offers the possibility to restrict the over aggregation of fused-ring nonfullerene acceptor in the process of film formation. During the kinetic process of anthracene removal in the blend under thermal annealing, donor can imbed into the remaining space of anthracene in the acceptor matrix to form well-developed nanoscale phase separation with bi-continuous interpenetrating networks. Consequently, the treatment of anthracene additive enables the power conversion efficiency (PCE) of PM6:Y6-based devices to 17.02%, which is a significant improvement with regard to the PCE of 15.60% for the reference device using conventional treatments. Moreover, this morphology controlling method exhibits general application in various active layer systems to achieve better photovoltaic performance. Particularly, a remarkable PCE of 17.51% is achieved in the ternary PTQ10:Y6:PC₇₁BM-based PSCs processed by anthracene additive. The morphology optimization strategy established in this work can offer unprecedented opportunities to build state-of-the-art PSCs.

Single-walled carbon nanotubes (SWCNTs) have been deployed in perovskite solar cells (PSCs) via a simple transfer route, achieving power conversion efficiencies of 19% and 18% on rigid and flexible substrates, respectively. Moreover, unique features of the SWCNT network, including the high environmental and chemical stability, outstanding mechanical robustness, have greatly extended the lifetime and durability of SWCNT-based PSCs.

Abstract

The unprecedented advancement in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has rendered them a promising game-changer in photovoltaics. However, unsatisfactory environmental stability and high manufacturing cost of window electrodes are bottlenecks impeding their commercialization. Here, a strategy is introduced to address these bottlenecks by replacing the costly indium tin oxide (ITO) window electrodes via a simple transfer technique with single-walled carbon nanotubes (SWCNTs) films, which are made of earth-abundant elements with superior chemical and environmental stability. The resultant devices exhibit PCEs of ≈19% on rigid substrates, which is the highest value reported to date for ITO-free PSCs. The facile approach for SWCNTs also enables application in flexible PSCs (f-PSCs), delivering a PCE of ≈18% with superior mechanical robustness over their ITO-based counterparts due to the excellent mechanical properties of SWCNTs. The SWCNT-based PSCs also deliver satisfactory performances on large-area (1 cm² active area in this work). Furthermore, these SWCNT-based PSCs can retain over 80% of original PCEs after exposure to air over 700 h while ITO-based devices only sustain ≈60% of initial PCEs. This work paves a promising way to accelerate the commercialization of ITO-free PSCs with reduced material cost and prolonged lifetimes.

Polyaromatic passivator 4-hydroxybiphenyl substituted naphthalene-1,8-dicarboximide provides chemical passivation (protonic/Lewis-base groups system) and energetic passivation (creating benign midgap states) effects. The Lewis-base/polyaromatic conjugation/protonic system reduces defects efficiently and avoids superoxide anions in perovskite solar cells.

Abstract

As game-changers in the photovoltaic community, perovskite solar cells are making unprecedented progress while still facing grand challenges such as improving lifetime without impairing efficiency. Herein, two structurally alike polyaromatic molecules based on naphthalene-1,8-dicarboximide (NMI) and perylene-3,4-dicarboximide (PMI) with different molecular dipoles are applied to tackle this issue. Contrasting the electronically pull–pull cyanide-substituted PMI (9CN-PMI) with only Lewis-base groups, the push–pull 4-hydroxybiphenyl-substituted NMI (4OH-NMI) with both protonic and Lewis-base groups can provide better chemical passivation for both shallow- and deep-level defects. Moreover, combined theoretical and experimental studies show that the 4OH-NMI can bind more firmly with perovskite and the polyaromatic backbones create benign midgap states in the excited perovskite to suppress the damage by superoxide anions (energetic passivation). The polar and protonic nature of 4OH-NMI facilitates band alignment and regulates the viscosity of the precursor solution for thicker perovskite films with better morphology. Consequently, the 4OH-NMI-passivated perovskite films exhibit reduced grain boundaries and nearly three-times lower defect density, boosting the device efficiency to 23.7%. A more effective design of the passivator for perovskites with multi-passivation mechanisms is provided in this study.

Two narrow-bandgap block copolymers PBDB-T-b-PIDIC2T and PBDB-T-b-PTY6 are designed and synthesized for single-component polymer solar cells, and a record-high efficiency of 8.64% is obtained. Moreover, these block copolymers exhibit relatively small energy loss and improved storage stability under both ambient condition and continued 80 °C thermal stresses for over 1000 h.

Abstract

Two narrow-bandgap block conjugated polymers with a (D1–A1)–(D2–A2) backbone architecture, namely PBDB-T-b-PIDIC2T and PBDB-T-b-PTY6, are designed and synthesized for single-component organic solar cells (SCOSCs). Both polymers contain same donor polymer, PBDB-T, but different polymerized nonfullerene molecule acceptors. Compared to all previously reported materials for SCOSCs, PBDB-T-b-PIDIC2T and PBDB-T-b-PTY6 exhibit narrower bandgap for better light harvesting. When incorporated into SCOSCs, the short-circuit current density (J _sc) is significantly improved to over 15 mA cm⁻², together with a record-high power conversion efficiency (PCE) of 8.64%. Moreover, these block copolymers exhibit low energy loss due to high charge transfer (CT) states (E _ct) plus small non-radiative loss (0.26 eV), and improved stability under both ambient condition and continuous 80 °C thermal stresses for over 1000 h. Determination of the charge carrier dynamics and film morphology in these SCOSCs reveals increased carrier recombination, relative to binary bulk-heterojunction devices, which is mainly due to reduced ordering of both donor and acceptor fragments. The close structural relationship between block polymers and their binary counterparts also provides an excellent framework to explore further molecular features that impact the photovoltaic performance and boost the state-of-the-art efficiency of SCOSCs.