Chen Weijie

A facile route is introduced to enhance the contact of NiO_X|perovskite by inserting a tetradecylamine (TeDA) interfacial layer, which modulates the wettability of NiO_X film and the transformation process of wet film to perovskite. Champion efficiency of 12.9% and improved stability are achieved for the larger area (53.64 cm²) perovskite solar modules based on spray-coated NiO_X.

Spray-coated nickel oxide (NiO_X) is a desirable hole-transporting material for perovskite solar cells (PSCs) because they are low cost, stable, and readily scalable. Recent research shows that the inferior interface contact of NiO_X|perovskite is the main factor that limits the efficiency and stability of the device. Herein, a facile route is introduced to enhance this contact by inserting a tetradecylamine (TeDA) interfacial layer. It is found that TeDA not only can modulate the wettability of NiO_X film, thus changing the transformation process of wet film to perovskite, but also can facilitate an efficient charge extraction at this interface. As a result, the efficiency of small-area (0.16 cm²) solar cells is improved from 15.8% to 18.7%. Moreover, a champion efficiency of 12.9% is achieved for the larger area (53.64 cm²) perovskite solar modules based on spray-coated NiO_X. The optimized devices also show improved stability in comparison with the devices without modification. This work provides a comprehensive understanding of the NiOx|perovskite interface and a new strategy for improving the perovskite quality and photovoltaic performance of PSCs.

The devices with 4-aminobutyric acid and 6-aminocaproic acid iodides forming 2D and 1D capping layers on the 3D films achieve high efficiencies of 23.48% and 23.11%, respectively, and show stable stability maintaining 93.73% and 91.58% of their initial efficiencies, respectively, after 2000 h exposure in atmosphere. 2D capping is more suitable for enhancing 3D perovskite performance than the 1D capping.

It has been reported that an overlayer of lower dimensional perovskite can effectively improve the properties of 3D perovskite solar cells. Here, 4-aminobutyric acid (C4I) and 6-aminocaproic acid iodides (C6I) are introduced onto the surface of the perovskite layer, forming a low-dimensional (LD) capping layer on the 3D perovskite films for high-performance devices. It is found that C4I forms a 2D perovskite layer, while C6I forms a 1D perovskite layer on the 3D perovskite surface. By using the LD capping layers, the integrated perovskite films show passivated surface traps, reduced defect density, improved carrier lifetimes, and altered band alignment, leading to improved fill factor and open-circuit voltage and, hence, significantly higher device efficiency. The devices with the C4I and C6I capping layers achieve solar cell efficiencies as high as 23.48% and 23.11%, respectively. In addition, bare devices with the C4I and C6I integration maintain 93.73% and 91.58%, respectively, of their initial efficiencies after exposure to the ambient atmosphere for 2000 h, demonstrating much better stability than the pristine 3D holding only 83.30% of its initial efficiency. It appears that this 2D capping is more suitable for enhancing 3D perovskite performance for general photoelectronic applications than the 1D capping.

Divalent transition metal complexes [Ni(NH₃)₆]F₂ or [Co(NH₃)₆]F₂ optimize the energy-level arrangement of an SnO₂ electron transport layer (ETL), passivate the defects of the ETL/perovskite interface, and improve the crystallinity of the perovskite layer.

For high-performance perovskite solar cells (PSCs), transition metal complexes as modifiers are used to optimize the energy-level alignment of the SnO₂ electron transport layer (ETL), reduce the defects at the ETL/perovskite interface, and improve the crystallinity of the perovskite layer. Herein, it is shown that application of [Ni(NH₃)₆]F₂ or [Co(NH₃)₆]F₂ complexes yields a substantially improved open-circuit voltage and fill factor, and thereby photoelectric conversion efficiency (PCE). The optimum PCEs of the [Ni(NH₃)₆]F₂- or [Co(NH₃)₆]F₂-treated PSCs reach 22.58% and 22.47%, respectively, which are much higher than that of the unmodified PSC (20.21%). This study provides a direction for improving the performance of a planar PSC using a complex-modified ETL.

Coordination of N-(4-acetylphenyl)maleimide with Pb²⁺ at the interface suppresses ion migration, as indicated by the temperature-dependent current response. Hole mobility increases from 10.74 to 19.48 cm² V⁻¹ s⁻¹ benefiting from the reduction in defects. Device with an average fill factor of over 80% and the maximum power conversion efficiency of 23.03% is achieved.

Abstract

Perovskite solar cells (PSCs) have made significant progress in power conversion efficiency (PCE) by optimizing deposition method, composition, interface, etc. Although the two-step method demonstrates the advantage of being easy to operate, too much residual PbI₂ not only forms defect centers, but affects the perovskite crystallization by arising more grain boundaries (GBs) due to the easy-to-crystallize nature of PbI₂. And GBs in polycrystalline perovskite usually provide main channel for ion migration, leading to accumulation of charges at the interface to form a barrier, thus reducing carrier mobility and resulting in degradation of perovskite devices. Here, an organic molecule N-(4-acetylphenyl)maleimide (N-APMI) is used to modify interface between perovskite and hole transport layer. X-ray photoelectron spectroscopy, scanning electron microscope, and nuclear magnetic resonance results show that ketone group (CO) in N-APMI forms a strong coordination with Pb²⁺, which effectively reduces the residual amount of PbI₂ nanoparticles on the perovskite surface, giving rise to improved crystallization of perovskite. Temperature-dependent current response demonstrates that ion migration is effectively suppressed, and hole mobility validly increases from 10.74 to 19.48 cm² V^–1 s^–1, leading to a champion fill factor (FF) of 82.5% (PCE 21.96%), and the maximum PCE of the device improves from 20.09% to 23.03%.

This work proposes a model to simulate the evolution of the perovskite precursor concentration, solvent vapor evaporation rate, and pressure in the annealing chambers. The results provide essential information for designing annealing chambers and tuning the crystallization process of perovskite solar cells.

Abstract

Triple-mesoscopic perovskite solar cells (PSCs) have attracted intensive attention due to the high stability, simple fabrication process, and low material cost. In this structure, the perovskite layer is hosted by a triple-mesoscopic scaffold of TiO₂/ZrO₂/carbon, and thus the crystal quality is sensitive to the thermal annealing process. Typically, the annealing process is conducted in a petri dish, for which the solvent evaporation of the perovskite precursor is slowed down, but not controllable and designable. To control the solvent evaporation, annealing chambers are first designed with different shape and vapor releasing channels. Then, physical simulations are performed by a finite element method, and it is found out that the chamber with a crowned top and releasing channels on the bottom sides can realize homogeneous distribution of the solvent vapor. To verify the simulation results, chambers are fabricated by 3D printing technique, for which the printing deviation can be as low as 100 µm. By balancing the solvent evaporation and release, the optimal solvent evaporation is achieved of the perovskite precursor in the triple-mesoscopic scaffold. This work offers a method to obtain homogeneous distribution of solvent vapor, and provides a new insight into understanding the influence of solvent evaporation during the thermal annealing process for PSCs.

A small molecule 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride (ABF) can promote the formation of pre-nucleated clusters, which act as nucleation templates at the gas-liquid interface, and induce top-down crystallization accompanied by uniform halide distribution. Ion vacancies and photo-induced halide phase separation are suppressed, exhibiting reduced V _oc deficit (from 0.55 V to 0.45 V) and enhanced long-term device stability.

Abstract

Mixed-halide perovskite has an irreplaceable role as wide-bandgap absorber in multi-junction tandem solar cells. However, large open-circuit voltage (V _oc) loss due to non-uniform halide distribution and compromised device stability due to photo-induced halide segregation has significantly limited the applications. Here, it is introduced 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride (ABF) with multifunctional groups (sulfonyl, ammonium, and fluoride) to the mixed-halide precursor to demonstrate a downward homogenized crystallization strategy for suppressing the initial vertical halide phase separation during perovskite crystallization and reducing V _oc loss. Furthermore, fluoride with strong electronegativity effectively fixes anions and cations, while sulfonyl and ammonium are used to passivate positive charged (halide vacancies) and negative charged (FA/MA vacancies) defects, respectively, thereby reducing the generation of ion vacancies that lead to subsequent photo-induced halide segregation. As a result, the 1.63 and 1.68 eV wide-bandgap perovskite solar cells with inverted structures exhibit the champion power conversion efficiency (PCE) of 21.76% and 20.11% with V _oc of 1.18 and 1.21 V, respectively. Most importantly, the optimized devices without encapsulation preserve 86% of initial efficiency after 240 h of continuous illumination under AM 1.5G, showing excellent light stability. Thus, the homogenized crystallization strategy provides highly efficient performance and stability for future tandem solar cell applications.

Publication date: July 2022

Source: Nano Energy, Volume 98

Author(s): Cheng Yang, Songlin Zhan, Qicong Li, Yulin Wu, Xiaohao Jia, Chao Li, Kong Liu, Shengchun Qu, Zhijie Wang, Zhanguo Wang

Here, methods to tune the work function of Ti₃C₂T _x are presented and the Ti vacancies in Ti₃C₂T _x are passivated by treatment with ethanolamine and metal chloride RhCl₃. The polymer solar cells with engineered Ti₃C₂T _x for electron or hole transport layers exhibit a power conversion efficiency of 15.88% or 15.54%. The modified Ti₃C₂T _x has a certain application prospect in photovoltaic devices.

Abstract

Ti₃C₂T _x , as a newly investigated 2D material, has gained great attention owing to its metallic conductivity, tunable work function (W _F), and unique electrical property. However, its W _F can be further adjusted to meet the needs of optoelectronic devices. Here, surface-engineered Ti₃C₂T _x is fabricated with tunable W _F by treating with ethanolamine and rhodium chloride (RhCl₃). Ethanolamine treated Ti₃C₂T _x can induce the chemical adsorption of NH₂ on Ti₃C₂T _x with hydrogen-bonding, which causes the decreased W _F, while chemical doping with RhCl₃ leads to the improvement of W _F, which is achieved by the downshift of Femi level of Ti₃C₂T _x . Moreover, the ethanolamine and RhCl₃ can effectively passivate the vacancies of Ti. As such, the surface-engineered Ti₃C₂T _x is more suitable as buffer layer for polymer solar cells (PSCs) by enhancing the interfacing characteristics of the Ti₃C₂T _x /active layer. The PSCs with engineered Ti₃C₂T _x for electron or hole transport layers can exhibit a power conversion efficiency of 15.88% or 15.54%. These efficiencies can be compared with those of devices with a conventional transport layer. This work provides a facile strategy to realize the work function tunability of Ti₃C₂T _x , and also shows that the tuned Ti₃C₂T _x has a certain application prospect in photovoltaic devices.

A non-fullerene acceptor, FO-EH-2Cl with branched alkyl side chains on the molecular backbone is designed to subtly manipulate the active layer morphology for all-small-molecule organic solar cells. A BSFTR:FO-EH-2Cl-based device achieves a power conversion efficiency (PCE) of 15.78% with an outstanding fill factor (FF) of 80.44%.

Abstract

Molecule engineering has been demonstrated as a valid strategy to adjust the active layer morphology in all-small-molecule organic solar cells (ASM-OSCs). In this work, two non-fullerene acceptors (NFAs), FO-2Cl and FO-EH-2Cl, with different alkyl side chains are reported and applied in ASC-OSCs. Compared with FO-2Cl, FO-EH-2Cl is designed by replacing the octyl alkyl chains with branched iso-octyl alkyl chains, leading to an enhanced molecular packing, crystallinity, and redshifted absorption. With a small molecule BSFTR as donor, the device of BSFTR:FO-EH-2Cl obtains a better morphology and achieves a higher power conversion efficiency (PCE) of 15.78% with a notable fill factor (FF) of 80.44% than that of the FO-2Cl-based device with a PCE of 15.27% and FF of 78.41%. To the authors’ knowledge, the FF of 80.44% is the highest value in ASM-OSCs. These results demonstrate a good example of fine-tuning the molecular structure to achieve suitable active layer morphology with promising performance for ASM-OSCs, which can provide valuable insight into material design for high-efficiency ASM-OSCs.

Three dopant-free polymeric hole transporting materials (HTMs) are developed based on different curvatures of the main backbone structure. The backbone curvatures of the polymeric HTMs affect the morphology and hole mobility of the HTMs and further change the crystallinity of perovskite films. Finally, the HTM with moderate molecular curvature exhibits the best performance in inverted perovskite solar cells.

Abstract

For achieving high-performance p-i-n perovskite solar cells (PSCs), hole transporting materials (HTMs) are critical to device functionality and represent a major bottleneck to further enhancing device stability and efficiency in the inverted devices. Three dopant-free polymeric HTMs are developed based on different linkage sites of triphenylamine and phenylenevinylene repeating units in their main backbone structures. The backbone curvatures of the polymeric HTMs affect the morphology and hole mobility of the polymers and further change the crystallinity of perovskite films. By using PTA-mPV with moderate molecular curvature, p-i-n PSCs with high efficiency of 19.5% and long-term stability can be achieved. The better performance is attributed to the more effective hole extraction ability, higher charge-carrier mobility, and lower interfacial charge recombination. Furthermore, these three polymeric HTMs are synthesized without any noble metal catalyst, and show great advantages in future application owing to the low-cost.

The type-II 2D/3D vertical heterojunction is created in tin-based perovskite films, which is favorable for charge transfer. Moreover, guanidinium thiocyanate additive is introduced to construct conducting channels for hole transfer in the 2D layer and reduce recombination loss in the whole films. The resultant solar cells show a record open circuit voltage of 1.01 V.

Abstract

2D–3D mixed tin halide perovskites are outstanding candidate materials for lead-free perovskite solar cells (PSCs) due to their improved stability and decreased trap density in comparison with their pure 3D counterparts. However, the mixture of multiple phases may lead to poor charge transfer across the films and limit the device efficiency. Here, a stacked quasi-2D (down)–3D (top) double-layered structure in perovskite films prepared via vacuum treatment is demonstrated, which can result in a planar bilayer heterojunction. In addition, it is found that the introduction of guanidinium thiocyanate (GuaSCN) additive can improve the crystallinity and carrier mobility in the 2D perovskite layer and passivate defects in the whole film, leading to a long carrier lifetime (>140 ns) in photoluminescence measurements. As a result, the PSCs show a high open circuit voltage (V_OC) up to 1.01 V with a voltage loss of only 0.39 V, which represents the record values ever reported for tin-based PSCs. The champion device exhibits a power conversion efficiency (PCE) of 13.79% with decent stability, retaining 90% of the initial PCE for 1200 h storage in N₂-filled glovebox.

Here, recent progress in the development of perovskite solar cells’ rear electrodes based on metals, carbon-based materials, transparent conductive oxides, and conductive polymers is summarized, especially focusing on their different impacts on the device's long-term stability and embedded degradation mechanisms. For practical applications, the impacts of rear electrodes on the device's overall efficiency and cost-effectiveness are also discussed.

Abstract

Perovskite solar cells (PSCs) represent a promising next-generation photovoltaic technology considering their high efficiency and low cost. At the current stage, resolving the stability bottleneck is extremely urgent to realize PSCs’ commercialization since the efficiencies of these cells are improved to a level comparable to that of crystalline silicon solar cells. Similar to other functional layers, a proper choice of the rear electrode atop the perovskite layer is equally important for achieving the device's long-term stability. This topic has not been comprehensively reviewed before. Here, recent progress in the development of rear electrodes based on metals, carbon-based materials, transparent conductive oxides, and conductive polymers is summarized, especially focusing on their different impacts on the device's long-term stability and associated degradation mechanisms. In the context of practical applications, the impacts of rear electrode materials on the device's overall efficiency and cost-effectiveness are also discussed.

Morphological modification is demonstrated to overcome the efficiency and lifetime limitations in organic photovoltaics (OPVs) for low-light applications. Ternary OPVs employing two well-miscible non-fullerene acceptors benefit from morphological optimization, which leads to suppressed charge recombination, and show exceptionally high efficiencies under low-intensity indoor light irradiation, offering guidance for indoor OPVs to surpass the currently dominant photovoltaic technologies.

Abstract

To meet the requirements for indoor organic photovoltaic (OPV) applications, it is imperative to minimize charge recombination loss and enhance photovoltaic performance toward commercially compelling levels. Here, morphological modification in non-fullerene blends is demonstrated to boost the efficiency and stability of indoor OPVs. For morphological modification, a ternary blend is devised by utilizing two well-miscible non-fullerene acceptors, which improve morphological features in the photoactive layer and suppress charge recombination loss. Morphological modification enhances OPV performance, particularly under low-intensity indoor irradiation conditions, at which trap-assisted recombination mainly governs the photovoltaic performance. The optimum ternary OPV shows a new record power conversion efficiency of 30.11% at a 500 lux light-emitting diode, accompanied by excellent morphological durability under thermal stress, despite the use of “existing” photovoltaic materials designed for AM 1.5 G operation. This study elucidates the effects of morphology on OPV performance under low-light conditions and suggests an ideal morphology for non-fullerene OPVs with enhanced performance for indoor applications.

Natural organic dye Indigo is for the first time demonstrated as a low-cost and highly efficient molecular passivator for high performance perovskite solar cells and the Indigo passivation boosts power conversion efficiency of device up to 23.22% as well as enhances device stability both in terms of humidity and thermal stress.

Abstract

Organic–inorganic hybrid lead halide perovskite solar cells have made unprecedented progress in improving photovoltaic efficiency during the past decade, while still facing critical stability challenges. Herein, the natural organic dye Indigo is explored for the first time to be an efficient molecular passivator that assists in the preparation of high-quality hybrid perovskite film with reduced defects and enhanced stability. The Indigo molecule with both carbonyl and amino groups can provide bifunctional chemical passivation for defects. In-depth theoretical and experimental studies show that the Indigo molecules firmly binds to the perovskite surfaces, enhancing the crystallization of perovskite films with improved morphology. Consequently, the Indigo-passivated perovskite film exhibits increased grain size with better uniformity, reduced grain boundaries, lowered defect density, and retarded ion migration, boosting the device efficiency up to 23.22%, and ≈21% for large-area device (1 cm²). Furthermore, the Indigo passivation can enhance device stability in terms of both humidity and thermal stress. These results provide not only new insights into the multipassivation role of natural organic dyes but also a simple and low-cost strategy to prepare high-quality hybrid perovskite films for optoelectronic applications based on Indigo derivatives.

A universal method of creating a dynamic healing interface (DHI) is launched by reinforcing the defective surface and grain boundaries of perovskite film with nonvolatile 2-bromonaphthalene (BN) with a low melting point of 53–58 °C. Different from static interfaces, the fluid characteristic originating from the easy solid-to-liquid phase conversion of the DHI not only reinforces management of defect passivation and energetics modification, but also enables effective defect real-time self-healing. High efficiencies are thus achieved for popular PSCs up to 12.05% (CsPbIBr₂), 14.14% (CsPbI₂Br), and 23.37% (FA_0.92MA_0.08PbI₃).

Abstract

Healing charge-selective contact interfaces in perovskite solar cells (PSCs) highly determines the power conversion efficiency (PCE) and stability. However, the state-of-the-art strategies are often static by one-off formation of a functional interlayer, which delivers fixed interfacial properties during the subsequent operation. As a result, defects formed in-service will gradually deteriorate the photovoltaic performances. Herein, a dynamic healing interface (DHI) is presented by incorporating a low-melting-point small molecule onto perovskite film surface for highly efficient and stable PSCs. Arising from the reduced non-radiative recombination, the DHI boosts the PCE to 12.05% for an all-inorganic CsPbIBr₂ solar cell and 14.14% for a CsPbI₂Br cell, as well as 23.37% for an FA_0.92MA_0.08PbI₃ (FA = formamidinium, MA = methylammonium) cell. The solid-to-liquid phase conversion of DHI at elevated temperature causes a longitudinal infiltration into the bulk perovskite film to maximize the charge extraction, passivate defects at grain boundaries, and suppress ion migration. Furthermore, the stability is remarkably enhanced under air, heat, and persistent light-irradiation conditions, paving a universal strategy for advanced perovskite-based optoelectronics.

Ammonium salt is utilized in NiO as a relatively neutral stabilizer to improve the stability and hole transport capability of NiO. Inverted MAPbI₃-based perovskite solar cells based on this novel NiO exhibit high power conversion efficiency (PCE) of 19.91% with exceptionally a high V _oc of 1.13 V and excellent stability, maintaining 97% of its initial PCE after 800 h.

Abstract

Nickel oxide (NiO) is one of the promising hole-transporting materials for perovskite solar cells (PSCs). Despite the ongoing efforts to improve PSC performance with sol–gel NiO, there has been limited study on the usage and influences of stabilizers on NiO and the relevant performance of PSCs. Until now, most of the sol–gel NiO methods use chemical stabilizers based on strongly acidic or mild basic catalysts such as hydrochloric acid and monoethanolamine. However, it is evident that the remaining pH-biased stabilizers in the film aggravate device stability. Therefore, it is imperative to develop a more stable and effective NiO, which can boost the performance of PSC. Here, the relatively neutral ammonium salt is utilized in NiO solution, which can improve the hole transport capability and stability of NiO. Under the optimum salt condition, energy level and hole conductivity are modulated favorably for hole transportation. Moreover, constructive interaction between the ammonium salt and perovskite enhances interfacial properties and reduces trap-assisted recombination. Based on this novel NiO, the champion power conversion efficiency of 19.91% with an exceptionally high open-circuit voltage of 1.13 V among the reported MAPbI₃-based PSCs is demonstrated. Furthermore, NiO with salt stabilizer secures long-term device stability, maintaining 97% of initial power conversion efficiency (PCE) even after 800 h.