JIALINGBO

Single-crystal-assembled perovskite thin film is achieved in this work. Photovoltaically top-performing (100) and (111) facets are directly proved based on the well-defined facets, leading to a stable perovskite solar cell with a PCE of 24.64%.

Herein, a siloxane derivative diethylphosphatoethylsilicic acid (PSiOH) is developed to modify the interface of TiO₂/FA_0.83Cs_0.17PbI₃. Comprehensive characteristics reveal that PSiOH can reduce surface defects, improve electrical properties and optimize energy band structure of TiO₂, and passivate Pb-related defects on the perovskite bottom surface. Consequently, PSiOH-modified perovskite solar cells (PSCs) yield a remarkable efficiency of 24.20% and improved stability.

Abstract

Suppressing defects at the interface between the TiO₂ electron transport layer (ETL) and perovskite film is critical for high efficiency and stable perovskite solar cells (PSCs). Herein, a siloxane derivative diethylphosphatoethylsilicic acid (PSiOH) is developed to modify the interface of TiO₂ ETL/FA_0.83Cs_0.17PbI₃ perovskite. Comprehensive characteristics reveal that silicon hydroxyl (SiOH) in PSiOH can reduce surface defects, improve the electrical properties and optimize the energy band structure of TiO₂ by forming a SiOTi bond, while the phosphate bond (PO) in PSiOH can passivate Pb-related defects on the perovskite bottom surface. Consequently, PSiOH-modified PSCs yield a remarkable power conversation efficiency of 24.20% and improved air, thermal, or illumination stabilities. This study provides insight into passivation defects at the buried interface for efficient and stable PSCs.

A pre-annealing treatment strategy is developed to reconstruct the sequentially deposited perovskite crystallites and GBs. The pre-annealing treatment suppresses perovskite decomposition from GBs, thereby having much less excess PbI2 on the perovskite top surface instead of at the conventional GBs. The resultant planar n-i-p-structured PSCs exhibit an impressive PCE approaching 25%.

In this review, the physical properties, different applications, advantages and disadvantages of fullerene, and its derivatives in perovskite solar cells (PSCs) are summarized and discussed. More importantly, the use of fullerenes to overcome well-known shortcomings in PSCs is discussed. This review can help in better understanding fullerenes and correlated different vital requirements to fabricate high-performance PSCs.

Abstract

Fullerene is one of the most critical materials that are widely used to improve and examine the inverted perovskite solar cells (PSCs, p-i-n structure). Fullerenes are known to improve the stability, lower the hysteresis, and increase the power conversion efficiency of the PSCs. Fullerene and its derivatives are often used in constructing effective PSCs. Several properties and performance of fullerenes are the key bases for testing and making effective alternatives that can improve the performance of PSCs. This review summarizes some of the most important fullerenes (i.e., fullerene and its derivatives) that are employed in inverted (p-i-n) PSCs and their physical properties that can overcome the well-known shortcomings in perovskite materials. The current density–voltage hysteresis in PSC and the fullerenes role in lowering the hysteresis are discussed. Moreover, fullerenes are also reviewed as electron transport layer, cathode buffer layer, and additives for perovskites. Enhanced stability by using fullerene derivatives is illustrated. Additionally, fullerenes in flexible and tandem PSCs as well as advantages and disadvantages of fullerenes are briefly discussed. Finally, an overview of the fullerene future in PSCs is discussed with alternative nonfullerene materials used in PSC.

A universal strategy is developed to subtly regulate the nucleation energetic barriers for large-scale patterning growth of high-quality perovskite single-crystal microplates with uniform morphology and exceptional electrical properties. Based on the perovskite single crystal arrays, high photoresponsivity and low device-to-device variation are achieved in the integrated photodetection circuits, enabling ultrasensitive, and high-contrast imaging functions.

Abstract

The pursuit of high-performance and integrated perovskite optoelectronic devices drives the development of efficient methods to pattern perovskite single crystals (PSCs). However, due to stochastic and multiple nucleation, PSCs obtained from traditional patterning methods still suffer from heterogeneous morphology and low crystallinity, resulting in unwanted large variation in the device performance. Herein, an effective and universal strategy is reported for the large-scale patterned growth of high-quality perovskite single-crystal microplates with uniform size and thickness. By modulating the wettability of gold nanoparticles, nucleation energetic barriers are subtly regulated and thus intractably random and multiple nucleation are fundamentally suppressed, enabling the formation of homogeneous perovskite microplates with exceptional properties in terms of ultralow surface defect density (6.1 × 10⁷ cm⁻²) and high carrier mobility (176 cm² V⁻¹ s⁻¹). In consequence, the photodetector array based on the patterned perovskite microplates exhibits a large photoresponsivity up to 615 A W⁻¹, along with a low photocurrent variable coefficient <5.2%, which enables the realization of ultrasensitive and high-contrast imaging functions. This patterning technique constitutes a major step toward the deployment of PSCs in integrated optoelectronic devices.

By employing 4,4'-sulfonyldiphenol (DSP) to passivate the perovskite surface, the intrinsic defect density is successfully modified and the oxidation of Sn²⁺ is suppressed. Furthermore, the resulting energy-level alignment significantly promotes the champion power conversion efficiency (PCE) of the hole transport layer-free Sn–Pb mixed narrow bandgap (E _g = 1.26 eV) perovskite solar cells to 21.43% with a V _oc of 0.876 V.

There have been a number of remarkable signs of progress achieved in tin–lead mixed narrow-bandgap perovskite solar cells (PSCs) due to the high theoretical power conversion efficiency (PCE) and their promising application in tandem devices. Indeed, Sn–Pb mixed PSCs without a hole transport layer (HTL) also have been more attractive owing to lower cost and simplification of the device structure. However, the defects in perovskite film introduced by Sn²⁺ oxidation severely restrict device efficiency and stability.Herein, a small organic molecule, 4,4'-sulfonyldiphenol, is employed to passivate perovskite (E _g = 1.26 eV) surface to decrease the interfacial defects and suppress the nonradiative carrier recombination. Furthermore, by regulating energy-level alignment, charge carrier extraction is greatly facilitated. The device performance is significantly enhanced in that the champion PCE is enlarged to 21.43% with an open-circuit voltage (V _oc) of 0.876 V from only 18.02% with a V _oc of 0.770 V. The stability of unencapsulated devices is improved substantially as well while retaining 80% PCE of its initial value after being stored in the glovebox for around 600 h. This facile but highly effective strategy successfully proposes the promising development of HTL-free Sn–Pb mixed PSCs.

The efficiency of the perovskite solar cell (PSC) is developing rapidly while its poor stability is still the fatal defect. Atomic layer deposition (ALD) provides some solutions for it. Herein, some typical cases reported in recent years for preparing PSCs buffer and encapsulation layers using ALD technology to improve device stability are reviewed.

Organic–inorganic mixed perovskite solar cells (PSCs) have been rapidly developed. However, while efficiency is improved, stability is still a problem that hinders further commercial production. Researchers have adopted many solutions and technological means to solve this problem, such as additive engineering, interface engineering, encapsulation engineering, and so on. To achieve the goal, various technical means have been employed. Among them, atomic layer deposition (ALD) is an effective tool to prepare compact pinhole-free thin films at low temperature, and its introduction provides some solutions to improve the stability of devices. Herein, the typical cases reported in recent years of preparing PSCs buffer and encapsulation layers using ALD technology to improve device stability are reported. The specific role of ALD in this process is analyzed, and the prospects and challenges of its further application are also discussed prospectively.

Engineers have achieved a power conversion efficiency of 23.50% in a perovskite-silicon tandem solar cell built with a special textured anti-reflective coating (ARC) polymeric film.

Publication date: 15 December 2022

Source: Nano Energy, Volume 104, Part A

Author(s): Tao Zhang, Qingquan He, Jiewen Yu, An Chen, Zenan Zhang, Jun Pan

The deployment of wide-bandgap perovskite solar cells requires that nonradiative recombination losses, especially at the interfaces between the perovskite and the transport layers (TLs), be reduced. It is shown that band alignment and traps are part of the story: the effective density of states (DOS) in the TL plays a key role in determining recombination and open-circuit voltage.

Wide-bandgap (≳1.7 eV) perovskite solar cells (PSCs) are plagued by relatively low open-circuit voltages. This is problematic as they are key to achieving perovskite silicon tandems, which can boost the potential of silicon solar cells. Performance in PSCs is widely considered to be limited by recombination at the interface between the perovskite and the transport layer (TL). Here, a number of design rules to increase the open-circuit voltage of wide-bandgap PSCs are introduced. A numerical device model that includes a detailed description of the interfacial recombination processes is presented. The combined effects of interface traps, ions, band alignment, and transport properties are introduced to identify the critical parameters for improving the open-circuit voltage. A large number of devices are simulated by picking random combinations of parameters and are looked for trends. It is shown that interface recombination can be suppressed by reducing the minority carrier density close to the interface with the TLs. It is demonstrated that the alignment of energy levels is only part of the story; the effective densities of states are of equal importance. The results pave the way to achieving high open-circuit voltages, despite a significant density of interface defects.

A multifunctional amino acid, L-aspartic acid (LAA) is utilized, to modify the SnO₂ surface and optimize the SnO₂/perovskite interface. Optimized perovskite solar cells (PSCs) are obtained with a high power conversion efficiency (PCE) of 22.63%, which is a 13% improvement over the device without LAA (20.02%). Besides, the stability performance of the PSCs modified by LAA is also remarkably improved.

Abstract

In n–i–p structured perovskite solar cells (PSCs), the electron transport layer (ETL)/perovskite interfaces greatly influence the power conversion efficiency (PCE) and stability of the devices. In recent years, more and more works have successfully prepared PSCs with excellent performance after employing tin dioxide (SnO₂) as ETL. However, oxygen vacancies and hydroxyl groups on the SnO₂ ETLs produced during preparation can easily induce defects at the film surface and injure the above perovskite film. Herein, a multifunctional amino acid, L-aspartic acid (LAA) is utilized, to modify the SnO₂ surface and optimize the SnO₂/perovskite interface. The carboxylic acid group of LAA can neutralize the alkalinity of the hydroxyl group on SnO₂ film, and the amino group of LAA can interact with the perovskite layer through the hydrogen bond, to adjust the crystallization process of perovskite film. Based on the double optimization of the SnO₂/perovskite interface, the defect density at the interface is greatly reduced, and the quality of the perovskite crystal is significantly improved. Finally, optimized PSCs are obtained with a high PCE of 22.63%, which is a 13% improvement over the device without LAA (20.02%). Besides, the stability performance of the PSCs modified by LAA is also remarkably improved.

The halide diffusion from perovskite can chemically dope the electron transport layer and bring forth the nonstoichiometric surface, leading to initial enhancement but long-term loss of the photovoltaic efficiency of p-i-n cells. A predoping strategy is developed to reach the diffusion equilibrium state for the fresh-fabricated device and delivers a power conversion efficiency of 23.13% with stable power output.

Abstract

Understanding the degradation mechanism of perovskite solar cells (PSCs) is of particular importance to solve their instability issue, which is one of the major hindrances toward commercialization. Here, it is shown that a halide diffusion equilibrium exists at the heterointerface of perovskite devices, which strongly impacts the evolution of device performance. The combined experimental and theoretical studies reveal that halide components diffuse from perovskite to fullerene layers in a p-i-n PSC device and equilibrate with an iodine density of 10¹⁸–10¹⁹ cm⁻³ within 80 h under dark aging condition. It is found that there is a strong correction between the device efficiency and halide diffusion equilibrium of PSCs, as the diffused halides can chemically dope the transport layer and result in the nonstoichiometric perovskite surface, leading to both initial enhancement and long-term loss of the photovoltaic efficiency of solar cells. In response to this issue, a predoping strategy is developed to attain the halide diffusion equilibrium once the device is fabricated, thereby avoiding the further halide migration and initial efficiency variations. As a result, the as-prepared PSC achieved an efficiency of 23.13% as well as stable power output under continuous one sun illumination.

An organic ammonium ion, ethylammonium (EA), is introduced to passivate defects caused by PbI₂ residue at the bottom of the perovskite film. EA also contributes to increasing crystallization quality and energy-level alignment at the interface. These changes are directly demonstrated by exposing the bottom interface. All photovoltaic parameters of perovskite solar cells are improved by introducing EA.

Abstract

The interface of perovskite solar cells (PSCs) plays a significant role in influencing their performance, yet there is still scarce research focusing on their difficult-to-expose bottom interfaces. Herein, ethylammonium bromide (EABr) is introduced into the bottom interface and its passivation effects are studied directly. First, EABr can improve substrate wettability, which is beneficial for the perovskite-film deposition. By lifting off the perovskite film spontaneously from the substrate, it is found that EABr can significantly reduce the amount of unreacted PbI₂ at the bottom interface. These PbI₂ crystals have been recently identified as a major defect source and degradation site for perovskite film. Meanwhile, EABr also lifts the valence band maximum at the bottom side of perovskite from -5.38 to -5.09 eV, facilitating better hole transfer. Such a improvement is also verified by the study of charge carrier dynamics. Through introducing EABr, all photovoltaic parameters of the inverted PSCs are improved, and their power conversion efficiency (PCE) increases from 20.41% to 21.06%. The study highlights the importance of direct characterization of the bottom interface for a better passivation effect.

A novel material of acetamidine thiocyanate (AASCN) has been designed and synthesized to functionalize on perovskite films, which synergistically improves crystallization and passivates surface defects, leading to an improved power conversion efficiency from 21.43% to 23.17%.

Further performance enhancement of perovskite solar cells (PSCs) is limited by the defect-assisted recombination losses. The approaches employed to decrease the losses contain defect passivation, perovskite crystallization control, interface engineering, etc. Herein, a new material of acetamidine thiocyanate (AASCN) via a facile method is synthesized, which exhibits dual functions combining a cation with passivation and an anion with crystallization. The iodine vacancies in the perovskite can be effectively passivated through hydrogen bonds formed by the NH bonds of the polar cation AA⁺. Furthermore, the pseudo-halide anion SCN⁻ can coordinate the Pb–I octahedrons, improving the perovskite film crystallization. Through vaporing the AASCN on perovskite films during the secondary crystal growth process, the defects mitigation and crystallization improvement are synergistically achieved. As a consequence, the FA_0.25MA_0.75PbI₃ PSCs with AASCN achieve a power conversion efficiency of 23.17%, which is higher than that (21.43%) of untreated PSCs. In detail, the open-circuit voltage has also a significant advancement from 1.095 to 1.167 V after the AASCN treatment. The design and synthesization of the multifunctional materials are supposed to provide a feasible approach for the performance improvement of PSCs.

A sulfur-containing Lewis base 2-(methylthio)ethylamine hydrochloride (MTEACl) as a perovskite precursor additive for p-MPSCs is adopted. The sulfur donor in MTEACl can interact with uncoordinated Pb²⁺, and thus effectively passivate defects in MAPbI₃ perovskite. Correspondingly, the trap density of the perovskite is reduced, contributing to the improvement of the power conversion efficiency from 15.18% to 17.17% and open circuit voltage to 995 mV.

In the rapid development of perovskite solar cells (PSCs), additive engineering has played a significant role for perovskite crystallization and passivation. The high density of defects at perovskite grain boundaries in the mesoporous scaffold leads to severe nonradiative recombination, which results in severe voltage loss. Herein, a sulfur-containing Lewis base 2-(methylthio)ethylamine hydrochloride (MTEACl) is applied in the perovskite precursor solution for printable mesoscopic PSCs with triple-mesoscopic layer structure. Due to the strong electron donating ability of sulfur, the MTEACl can strongly interact with Pb²⁺, which can effectively passivate the defects of the perovskite. Correspondingly, the trap density of the perovskite is reduced, contributing to the improvement of power conversion efficiency from 15.18% to 17.17% and open circuit voltage to 995 mV.

Three polymer analogues to polyaniline (PANI), PANI–carbazole (P1), PANI–phenoxazine (P2), and PANI–phenothiazine (P3) are designed with different energy levels to modify the interface between poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and the MAPbI₃-based perovskite layer and improve the device performance. The order of contribution for the three effects of the polymer modification is work function adjustment > surface modification > perovskite growth control.

Abstract

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a popular hole transport material in perovskite solar cells (PSCs). However, the devices with PEDOT:PSS exhibit large open-circuit voltage (V _oc) loss and low efficiency, which is attributed to mismatched energy level alignment and the poor interface of PEDOT:PSS and perovskite. Here, three polymer analogues to polyaniline (PANI), PANI–carbazole (P1), PANI–phenoxazine (P2), and PANI–phenothiazine (P3) are designed with different energy levels to modify the interface between PEDOT:PSS and the perovskite layer and improve the device performance. The effects of the polymers on the device performance are demonstrated by evaluating the work function adjustment, perovskite growth control, and interface modification in MAPbI₃-based PSCs. Low bandgap Sn–Pb-based PSCs are also fabricated to confirm the effects of the polymers. Three effects are evaluated through the comparison study of PEDOT:PSS-based organic solar cells and MAPbI₃ PSCs based on the PEDOT:PSS modified by P1, P2, and P3. The order of contribution for the three effects is work function adjustment > surface modification > perovskite growth control. MAPbI₃ PSCs modified with P2 exhibit a high V _oc of 1.13 V and a high-power conversion efficiency of 21.06%. This work provides the fundamental understanding of the interface passivation effects for PEDOT:PSS-based optoelectronic devices.

An amine salts vapor healing strategy is applied to simultaneously passivate the defects across the entire perovskite film and obstruct the interfacial redox reaction between NiO_x and perovskite, enhancing both the device performance and the performance consistency. The vapor healing strategy substantially reduces the trap density and promotes device power conversion efficiency from 17.92% to 20.48% with improved operational device stability.

Abstract

Post-treatment is a widely used strategy to reduce defects in perovskite films, but has been largely limited to the solution phase. Herein, the posttreatment tool kit and develop a universal amine salts (A^IX^I) vapor healing strategy by taking advantage of the penetrating power of vapor and the soft-matter characteristics of halide perovskite is expanded. In a striking demonstration, the post-treatment of pristine perovskite layers allows simultaneous filling of the MA⁺ and I^– vacancies, passivation of both the cation and anion defects, and healing of the films to high order and high crystallinity required for high device performance, from the surface to the bulk and all the way down to the bottom. Experiments and DFT calculations revealed that charge extraction can be enhanced and non-radiative recombination can be reduced by regulating the energy levels and reducing the trap states via the A^IX^I vapor healing. Moreover, the diffusing A^IX^I can reach the NiO_x surface to obstruct the undesirable interfacial reactions and passivate the interface defects, further reducing the open-circuit voltage (V _oc) loss. The vapor healing strategy substantially reduces the trap density from 4.76 × 10¹⁵ to 1.04 × 10¹⁵ cm^–3, and promots power conversion efficiency of the champion device from 17.92% to 20.48% with superior device consistency, V _oc up to 1.114 V and the operational device stability.

High-performance inverted planar perovskite solar cells with a high-quality perovskite layer and excellent interfacial contacts are fabricated via partially replacing of dimethyl sulfoxide with N-methyl-2-pyrrolidinone, and a champion power conversion efficiency of 21.53% is achieved with remarkably enhanced humidity and thermal stabilities even without any encapsulation.

Herein, a very simple but efficient method is developed to concurrently improve the quality of perovskite film and enhance the interfaces of perovskite solar cells (PSCs) concurrently via partially replacing dimethyl sulfoxide (DMSO) with N-methyl-2-pyrrolidinone (NMP) in inverted planar PSCs. With the systematic investigations, it is found that the perovskite films fabricated with this simple method demonstrate higher crystallinity, larger grain size with less grain boundaries, and better perovskite–substrate interface with very rare voids. All of these lead to efficient all-round defects suppression and high performance of the corresponding PSCs. As a result, the tri-mixed solvent (DMF:DMSO:NMP = 4:0.75:0.25) processing renders a power conversion efficiency (PCE) of 21.53%, which is much higher than that of PSCs fabricated with traditional bi-mixed solvent (DMF:DMSO = 4:1) (only 17.05%). Notably, the simple-method-fabricated PSCs demonstrate remarkable humidity and thermal stabilities even without any encapsulation (90.6% and 75.2% of initial PCE are retained after more than 511 h in air with relative humidity (RH) ≈ 50% at room temperature and 216 h in air with RH 70% at continuous heating of 70 °C, respectively). All these results demonstrate that the simple method by partially replacing DMSO with NMP is very efficient to improve the quality of perovskite layer and yield high-performance PSCs.

The Spiro-BD-2OEG with composition-conditioning agent functionality is designed to improve the composition stability in the doped-Spiro-OMeTAD hole transport layer (HTL). By employing this strategy, the HTL shows a pinhole-free and smooth morphology with an enhanced Spiro-OMeTAD ordering. Finally, the resultant perovskite solar cells show an excellent power conversion efficiency of 24.19% and improved thermal, moisture, and operational stabilities.

Abstract

The doped Spiro-OMeTAD hole transport layer (HTL) formed using the lithium bis(trifluoromethane) sulfonimide salt and 4-tert-butylpyridine with phenethylammonium iodide surface treatment on a perovskite film has continuously dominated the record power conversion efficiencies (PCEs) of perovskite solar cells (pero-SCs). However, unstable HTL compositions and iodide salts can cause severe device degradation. In this study, an HTL composition-conditioning agent (CCA), Spiro-BD-2OEG, is designed, which contains a Spiro-OMeTAD-like backbone, functional pyridine units, and oligo (ethylene glycol) chains. This finely designed CCA presents good miscibility with Spiro-OMeTAD and its dopants and acts as a conditioning agent through weak bond interactions. As a result, the CCA-regulated HTL shows a pinhole-free and smooth morphology with enhanced Spiro-OMeTAD ordering and improves dopant stability. In addition, the gradient-distributed CCA in the HTL can narrow the energy level offset with the valence band of the perovskite. The resultant pero-SCs exhibit an excellent PCE of 24.19% without any interface treatment and weak size dependence. A remarkable PCE of 22.63% is obtained even for a 1.004-cm² device. Importantly, the strategy shows good universality and significantly promotes the long-term stability of the pero-SCs based on the classical doped Spiro-OMeTAD.

Two key interfaces on either side of the metal-halide perovskite thin film in flexible perovskite solar cells (f-PSCs) are reinforced simultaneously. This new class of dual-interface-reinforced f-PSCs has an unprecedented combination of high efficiency (21.03%), improved operational stability (1000 h T ₉₀), and enhanced mechanical reliability (10 000 cycles n ₈₈). The scientific underpinnings of these synergistic enhancements are elucidated.

Abstract

Two key interfaces in flexible perovskite solar cells (f-PSCs) are mechanically reinforced simultaneously: one between the electron-transport layer (ETL) and the 3D metal-halide perovskite (MHP) thin film using self-assembled monolayer (SAM), and the other between the 3D-MHP thin film and the hole-transport layer (HTL) using an in situ grown low-dimensional (LD) MHP capping layer. The interfacial mechanical properties are measured and modeled. This rational interface engineering results in the enhancement of not only the mechanical properties of both interfaces but also their optoelectronic properties holistically. As a result, the new class of dual-interface-reinforced f-PSCs has an unprecedented combination of the following three important performance parameters: high power-conversion efficiency (PCE) of 21.03% (with reduced hysteresis), improved operational stability of 1000 h T ₉₀ (duration at 90% initial PCE retained), and enhanced mechanical reliability of 10 000 cycles n ₈₈ (number of bending cycles at 88% initial PCE retained). The scientific underpinnings of these synergistic enhancements are elucidated.

A sustainable dynamic passivation strategy by incorporating a photoisomeric molecule is put forward, which greatly enhances the photostability of perovskite photovoltaics. This dynamic strategy pays attention to and well matches the dynamics of defect generation during operation. The characteristics of the changeable molecular structure enable us to cope with defects updated in operation without introducing excess active sites.

Abstract

The generation of photoinduced defects and freely moving halogen ions is dynamically updated in real time. Accordingly, most reported strategies are static and short-term, which make their improvements in photostability very limited. Therefore, seeking new passivation strategies to match the dynamic characteristics of defect generation is very urgent. Without newly generated defects, a passivation molecule should exist in the configuration that would not become the initiation sites for defect generation. With newly generated defects, the passivation molecule should transfer into the other configuration that possesses the passivation sites. Herein, a classical photoisomeric molecule, spiropyran, is adopted, whose pre- and post-isomeric forms meet the requirements for two different configurations, to realize the state transition once the photoinduced defects appear during subsequent operation and dynamic capture for continuous renewal of defects. Consequently, spiropyrans work as light-triggered and self-healing sustainable passivation sites to realize continuous defect repair. The target devices retain 93% and 99% of their initial power conversion efficiencies after 456 h aging under ultraviolet illumination and 1200 h aging under full-spectrum illumination, respectively. This work provides a novel concept of sustainable passivation strategy to realize continuous defect-passivation and film-healing in perovskite photovoltaics.

Foldable perovskite solar cells (PSCs) are constructed by using ultrathin copper (Cu) electrodes with low reactivity, combined with potassium methacrylate (KMMA) additive. Benefitting from dual function of KMMA additive for controlling perovskite films crystallization and binding halogen ion, ultrathin Cu-based PSCs exhibit improved power conversion efficiency, as well as excellent thermal and operational stability.

Abstract

Perovskite solar cell (PSC) using ultrathin metal transparent electrode is a promising power source for wearable electronics and aerospace applications. However, the environmental stability of device is challenging, due to the undesirable interdiffusion of metal and halogen ions. In this work, PSCs are constructed by using ultrathin copper (Cu) electrodes with low reactivity, combined with potassium methacrylate (KMMA) additive. On one hand, carbonyl groups in KMMA interact with the perovskite and improve quality of perovskite films. As a result, the power conversion efficiency (PCE) of ultrathin Cu-based PSC is increased from 12.49% to 14.72%. On the other hand, benefitting from the binding of K⁺ with halogen ion, the interdiffusion of Cu and I ions is hindered. Thus, PSCs retain 80% and 75% of the initial PCE under heating at 85 °C for 130 h and maximum power point for 300 h, respectively. To the best of the knowledge, it is one of the best thermal and operational stability for the PSCs using metal-based electrodes. At last, the symmetric PSCs exhibit superior folding stability which maintain 85.3% of initial PCE after folding for 500 cycles. Foldable PSCs on ultrathin Cu electrodes with excellent stability are attractive power sources in wearable applications.

The interfacial engineering using hole-selective self-assembled monolayers is vital to enhance power conversion efficiencies and stabilities of next generation photovoltaics.

Abstract

Inverted type perovskite solar cells (PSCs) have recently emerged as a major focus in academic and industrial photovoltaic research. Their multiple advantages over conventional PSCs include easy processing, hysteresis-free behavior, high stability, and compatibility for tandem applications. However, the maximum power conversion efficiency (PCE) of inverted PSCs still lags behind those of conventional PSCs because suitable charge-selective materials for inverted PSCs are limited. In this study, excellent hole-selective materials for inverted PSCs are introduced. A series of tricyclic aromatic rings containing O, S, or Se, respectively, as a core heteroatom, along with a phosphonic acid anchor, form a self-assembled monolayer (SAM) that directly contacts the perovskite absorber. The influence of heteroatoms in the aromatic structure on the molecular energetics and operating characteristics of the corresponding inverted PSCs is investigated using complementary experimental techniques as well as density functional theory (DFT) calculations. It is found that all of the SAMs formed an energetically well-aligned interface with the perovskite absorber. The interaction energy between the Se-containing SAM and perovskite absorber is the strongest among the series and it reduces the interfacial defect density, in turn leading to an extended charge carrier lifetime. As a result, PSCs incorporating the Se-containing SAM achieves a PCE of 22.73% and retains ≈96% of their initial efficiency after a maximum power point tracking test of 500 h without encapsulation under ambient conditions. All of the SAMs are then employed in organic solar cells (OSCs). Again, the Se-containing SAM-based OSCs demonstrates the highest PCE of 17.9% among the three molecular SAM-based OSCs. This study demonstrates the great potential for precisely engineered SAMs for use in high-performance solar cells.

Through machine learning, the influences of five factors, including grain size, defect density, bandgap, fluorescence lifetime, and surface roughness, on the efficiency and stability of perovskite solar cells have been revealed. The surface roughness and grain size are most influential to the long-term stability. A mathematical model is given to predict efficiency based on fluorescence lifetime and bandgap.

Abstract

Understanding the key factor driving the efficiency and stability of semiconductor devices is vital. To date, the key factor influencing the long-term stability of perovskite solar cells (PSCs) remains unknown because of the many influencing factors. In this work, through machine learning, the influences of five factors, including grain size, defect density, bandgap, fluorescence lifetime, and surface roughness, on the efficiency and stability of PSCs have been revealed. It is found that the bandgap has the greatest influence on the efficiency, and the surface roughness and grain size are most influential to the long-term stability. A mathematical model is given to predict efficiency based on fluorescence lifetime and bandgap. Guided by the model, four groups of experiments are conducted to confirm the machine-learning predictions and a PSC with 23.4% efficiency and excellent long-term stability is obtained, as manifested by retention of 97.6% of the initial efficiency after 3288 h aging in the ambient environment, the best stability under these conditions. This work shows that machine learning is an effective means to enrich semiconductor physical models.

The roles of electrode materials and interfaces in perovskite solar cell (PSC) devices are discussed in terms of perovskite stability. The various factors responsible for rapid degradation in PSCs are provided. Then, the roles of carbonaceous materials for carbon-based PSC as a substitute for noble metals are addressed, along with the recent progress.

Abstract

Exceptional power conversion efficiency (PCE) of 25.7% in perovskite solar cells (PSCs) has been achieved, which is comparable with their traditional rivals (Si-based solar cells). However, commercialization-worthy efficiency and long-term stability remain a challenge. In this regard, there are increasing studies focusing on the interface engineering in PSC devices to overcome their poor technical readiness. Herein, the roles of electrode materials and interfaces in PSCs are discussed in terms of their PCEs and perovskite stability. All the current knowledge on the factors responsible for the rapid intrinsic and external degradation of PSCs is presented. Then, the roles of carbonaceous materials as substitutes for noble metals are focused on, along with the recent research progress in carbon-based PSCs. Furthermore, a sub-category of PSCs, that is, flexible PSCs, is considered as a type of exceptional power source due to their high power-to-weight ratios and figures of merit for next-generation wearable electronics. Last, the future perspectives and directions for research in PSCs are discussed, with an emphasis on their commercialization.

Three novel self-doped molecules named t-PyDIN, t-PyDINO and t-PyDINBr are developed as cathode interfacial materials for OSCs. The devices based on t-PyDINBr and t-PyDINO exhibit PCEs of 17.24 % and 17.56 %, respectively. Notably, the device based on t-PyDIN even reached a PCE of 18.25 %, which is improved by 51.3 % compared with that of the device without a cathode interfacial layer. This result is among the best efficiencies reported to date.

Abstract

Efficient cathode interfacial layers (CILs) are becoming essential elements for organic solar cells (OSCs). However, the absorption of commonly used cathode interfacial materials (CIMs) is either too weak or overlaps too much with that of photoactive materials, hindering their contribution to the light absorption. In this work, we demonstrate the construction of highly efficient CIMs based on 2,7-di-tert-butyl-4,5,9,10-pyrene diimide (t-PyDI) framework. By introducing amino, amino N-oxide and quaternary ammonium bromide as functional groups, three novel self-doped CIMs named t-PyDIN, t-PyDINO and t-PyDINBr are synthesized. These CIMs are capable of boosting the device performances by broadening the absorption, forming ohmic contact at the interface of active layer and electrode, as well as facilitating electron collection. Notably, the device based on t-PyDIN achieved a power conversion efficiency of 18.25 %, which is among the top efficiencies reported to date in binary OSCs.

A room-temperature molten salt dimethylamine acetate is developed as the solvent for precursor solutions, which also regulates the phase conversion process of the CsPbI₃ film. Consequently, 1.25 V of the open-circuit voltage and >21% power conversion efficiency are achieved, which is the record highest for CsPbI₃ perovskite solar cells reported so far.

Abstract

All-inorganic CsPbI₃ perovskite has emerged as an important photovoltaic material due to its high thermal stability and suitable bandgap for tandem devices. Currently, the cell performance of CsPbI₃ solar cells is mainly subject to a large open-circuit voltage (V _OC) deficit. Herein, a multifunctional room-temperature molten salt, dimethylamine acetate (DMAAc) is demonstrated, which not only directly acts as a solvent for precursor solutions, but also regulates the phase conversion process of the CsPbI₃ film for high-efficiency photovoltaics. DMAAc can stabilize the DMAPbI₃ structure and eliminate the Cs₄PbI₆ intermediate phase, which is easily spatially segregated. Meanwhile, a new homogeneous intermediate phase DMAPb(I,Ac)₃ is formed, which finally affords high-quality CsPbI₃ films. With this approach, the charge capture activity of defects in the CsPbI₃ film is significantly suppressed. Consequently, a V _OC of 1.25 V and >21% power conversion efficiency are achieved, which is the record highest reported thus far. This intermediate phase-regulation strategy is believed to be applicable to other perovskite material systems.