Mahui

Sodium dodecyl benzene sulfonate (SDBS) is used as a multifunctional chemical additive for efficient and stable planar fully air‐processed perovskite solar cells (PSCs). The introduction of SDBS can promote the preferential growth of crystal orientation, reduce defects, inhibit the migration of iodide ions, enhance the built‐in potential, and improve the water resistance of perovskite films.

The device performance of organic–inorganic hybrid halide perovskite solar cells (PSCs) is highly dependent on the quality of perovskite layer. Herein, a multifunctional chemical additive strategy is reported to simultaneously improve the efficiency and stability of fully air‐processed PSCs. The planner methylammonium lead trihalide (MAPbI₃)‐based PSCs incorporating sodium dodecyl benzene sulfonate (SDBS) exhibit a champion power conversion efficiency (PCE) of 19.20% and negligible hysteresis, which is one of the top efficiencies of MAPbI₃‐based PSCs made in air. The increased efficiency is due to the reduction of defects and inhibition of ion migration in the perovskite films. Furthermore, the enhancement of device performance and stability can also be ascribed to highly preferred and efficient perovskite crystals protecting the perovskite films from humidity. The corresponding unencapsulated device retains 92.34% of its initial efficiency after 90 days (>2100 h) storage in air and maintains 85.20% of its original PCE after being exposed to 85 °C for 27 h. The results indicate that SDBS is a promising chemical additive to enhance the performance of air‐processed PSCs for future applications.

Pinhole‐free perovskite films with large grains are fabricated in ambient air by a spinning–bathing–spinning method. The effects of moisture on the formation of I‐dominant grain and Cl‐enriched boundaries and surfaces in the perovskite films are revealed, which enable the air‐processed perovskite solar cells with a high efficiency of more than 20%.

Metallic halide perovskite films are usually fabricated in inert environment due to their high sensitivity to moisture and oxygen. However, the fabrication process in the strictly controlled environment is not economical for mass production. Therefore, the fabrication of high‐quality perovskite films in ambient air is more practical for optoelectronic devices. Herein, a spinning–bathing–spinning (SBS) method is demonstrated to deposit pinhole‐free perovskite films with large grains in ambient air for solar cells. The effect of moisture on the rapid crystallization and grain coarsening can be suppressed using this SBS method. Furthermore, the moisture is found to encourage the halogen separation in the perovskite films when using PbI₂–PbCl₂ as the lead halide precursor, resulting in the formation of I‐dominant perovskite grains and Cl‐enriched boundaries and surface in the films. The Cl‐enriched grain boundaries and film surface, which mainly originate from the confined methylammonium chloride (MACl), can passivate defects and prevent further damage from moisture and oxygen. This spontaneous inner‐to‐outside passivation enables the air‐processed perovskite solar cells with the high power conversion efficiencies of more than 20% and improved stability.

Different concentrations of ester‐substituted thiophene are introduced into the conjugated backbone of the polymer acceptor to rationally adjust the aggregation behaviors, absorption properties, and energy levels, and finally improve the photovoltaic performance of the PYEx‐based all‐polymer solar cells. Among them, blends of PYE2 with polymer donor PBDB‐T are achieved with a maximum power conversion efficiency (PCE) of 13.57%.

Finding effective molecular design strategies and fine tuning the molar ratios of donor/acceptor (D/A) random copolymers to optimize the blend microstructure of the photoactive layer is one of the main long‐standing challenges in developing and fabricating highly efficient all‐polymer solar cells (all‐PSCs). Herein, a random ternary copolymerization strategy to develop four random copolymer acceptors PYEx (x = 10, 20, 30, 40) is used by polymerizing a fused‐ring A–D–A‐type acceptor unit modified from Y5 with a thiophene‐connecting unit and a controlled amount of an ester‐substituted thiophene (EST) unit. Compared with PYT (PYE0) of only Y5‐like units and thiophene units, the ternary copolymers PYEx show slightly down‐shifted lowest unoccupied molecular orbital (LUMO) energy levels, reduced absorption coefficients, and decreased electron mobilities. However, it is also demonstrated that this design approach rationally modifies the molecular aggregations of polymer acceptors, effectively fine tuning the blend morphology and physical mechanisms, and enhances the device performance of the PYEx‐based all‐PSCs. Among them, blends of PYE20 with donor polymer PBDB‐T combine 13.6% power conversion efficiency (PCE). Of particular note is that all of the PYEx‐based devices exhibit the best PCEs of over 13%, indicating the high tolerance on molar ratios.

Organic‐inorganic hybrid perovskite materials have emerged as promising photovoltaic candidates. Herein, a supramolecular complex [(C₈H₁₇)₄N]₄[SiW₁₂O₄₀] is synthesized and introduced into SnO₂ to produce a mutifunctionalized electron transport layer (ETL). Suppressed trap state density and improved band alignment are attained in modified perovskite solar cells. Devices with [(C₈H₁₇)₄N]₄[SiW₁₂O₄₀] show a champion efficiency of 22.84% and stable performance under irradiation.

Recently, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been developed to exceed 25%, and charge transport layer optimization is a promising strategy for further efficiency improvement in PSCs. Herein, a supramolecular complex [(C₈H₁₇)₄N]₄[SiW₁₂O₄₀] (TASiW‐12) is synthesized and its doped form in SnO₂ (hereafter S‐SnO₂) is used as a charge transport layer (electron transport layer, ETL). This study demonstrates that S‐SnO₂ introduction is a practical and effective way to improve the bulk ETL and those of the ETL/perovskite interface. S‐SnO₂ leads to improved band alignment, suppressed trap‐assisted charge recombination, and enhanced electron mobility. In addition, an enhanced open‐circuit voltage (V _oc) of 1.16 V and an efficiency of 22.8% are successfully achieved in n–i–p planar PSCs. Meanwhile, S‐SnO₂ acts as a crucial agent to reduce charge accumulation at the S‐SnO₂/perovskite interface. The device possesses superior stability for 3072 h with only a 5.65% loss of the initial PCE. These results indicate that high‐efficiency PSCs can be easily attained by introducing a TASiW‐12‐doped ETL with integrated functions.

An interfacial layer of triphenylamine–polystyrene blend is used between the perovskite layer and charge‐transporting layer to concurrently suppress energy loss and improve device stability. The energy loss is reduced from 0.49 to 0.35 eV, along with a large open‐circuit voltage of 1.18 V and a high power conversion efficiency of 22.1% in air‐stable perovskite solar cells.

Energy loss induced by nonradiative recombinations plays a critical role in determining power conversion efficiencies in perovskite solar cells, whereas device stability impacts their long‐time reliability in the ambient environment. It is an important challenge to suppress energy loss and improve device stability simultaneously. Herein, an interfacial layer of triphenylamine (TPA):polystyrene (PS) blend coated on the hybrid perovskite layer to concurrently suppress energy loss and improve device stability is reported. The energy loss is suppressed from 0.49 to 0.35 eV by passivating surface defects in hybrid perovskites via Lewis acid–base interactions with the combination of electron‐donating aromatic nucleus in PS and tertiary amine in TPA, leading to perovskite solar cells with a high open‐circuit voltage of 1.18 V, a fill factor of about 80%, and a power conversion efficiency of 22.1%. Meanwhile, the device stability in the ambient environment is improved significantly by the TPA:PS blend due to its superior hydrophobicity which is suggested by its high contact angle of 91.1° as compared to 64.0° for the pristine perovskite film. Herein, an efficient interfacial engineering approach with the TPA:PS blend to suppress energy loss and improve device stability simultaneously towards realistic applications is demonstrated.

Inorganic CsPbI3 perovskite is the most competitive candidate to hybrid perovskites. However, its poor phase stability, hydrophobicity and high‐density defects have limited the development of CsPbI3 perovskite solar cells (PSCs). To overcome these obstacles for achieving high‐performance CsPbI3 PSCs, additive engineering has been widely employed. Herein, the progress of additive engineering in CsPbI3 PSCs is systematically reviewed.

All‐inorganic perovskite solar cells (PSCs) have attracted a lot of attention in the past few years because of their preeminent thermal stability compared with organic–inorganic hybrid PSCs. Among all kinds of all‐inorganic perovskites, CsPbI₃ perovskite with a proper bandgap of ≈1.7 eV becomes the most competitive candidate. However, its poor phase stability, hydrophobicity, and high‐density defects have limited the development of CsPbI₃ PSCs. To overcome these obstacles for achieving high‐performance CsPbI₃ PSCs, additive engineering has been widely used, which has rapidly promoted the power conversion efficiency (PCE) to over 19%. Herein, the progress of additive engineering in CsPbI₃ PSCs is systematically reviewed. First, the roles of additives in CsPbI₃ PSCs are introduced, including improving phase stability, increasing moisture resistance, and passivating defects. Then, the additive engineering is categorized (additive engineering in perovskites and at perovskite/hole transport layer interfaces) and reviewed in detail. Finally, future research directions on additive engineering are suggested for further enhancing stability and improving PCE.

The commercially available pyridinedicarboxylic acid (PDA) molecule with one pyridine and two carboxylic acid groups is used as a passivating agent to cure the defects at both the surfaces and grain boundaries of MAPbI₃ perovskites. A champion power conversion efficiency (PCE) approaching 19% with optimized long‐term stability and thermal stability is achieved in PDA‐passivated perovskite solar cells (PSCs).

Electronic defects and grain boundaries of perovskite films will significantly deteriorate both the efficiency and the stability of perovskite solar cells (PSCs), and various methods aimed to reduce these defects are proposed. Herein, an organic solid molecule of pyridinedicarboxylic acid (PDA) with one pyridine and two carboxylic acid groups is used as a passivating agent to cure the defects by regulating the perovskite microstructures in a multiple manner. The defects located at both the surfaces and grain boundaries of polycrystalline MAPbI₃ perovskites are simultaneously passivated through the multiple coordination effects between the used functional groups and uncoordinated Pb²⁺, regardless of the substitution sites of the carboxylic acid and pyridine. Impressively, the PDA‐passivated inverted PSCs achieve remarkably enhanced power conversion efficiencies (PCEs) from 16.43% to nearly 19% and maintain over 90% of its original PCE after 1300 h under an inert environment. These findings indicate that the commercially available PDA molecule emerges as an efficient passivating agent of perovskite defects capable of stimulating the combined effects of the multiple functional groups, which is highly promising for the practical applications of PSCs with both high efficiency and good stability.

A mixed lead precursor of halide lead source and nonhalide lead source is used to enable a low‐temperature, two‐step sequential deposition method for FAPbI₃ perovskite in triple‐mesoscopic solar cells. A power conversion efficiency of 16.21% is achieved.

The evolution from the original methylammonium (MA)‐ to formamidinium (FA)‐dominated perovskite makes a crucial contribution to improve the photoelectric performance of perovskite solar cells (PSCs) in a decade. However, to obtain α‐FAPbI₃, annealing temperature above 100 °C is essential. In addition, it is still challenging to deposit a uniform and high‐quality FA‐based perovskite absorber in printable triple‐mesoscopic PSC due to the complicated mesoscopic structure. Herein, a low‐temperature, two‐step sequential deposition method is used for pure FAPbI₃ perovskite in printable triple‐mesoscopic PSC. By using different lead sources, the crystallization and morphology of lead iodide (PbI₂) are finely controlled, which modulates the crystallization and pore filling of perovskite in mesoscopic structure. The improved interface contact promotes the transfer of charge carrier from perovskite to TiO₂. With the further introduction of cesium bromide (CsBr) into lead precursor, a power conversion efficiency of 16.24% is achieved. This study provides a deeper understanding of the pore filling and crystallization for both PbI₂ and perovskite, and helps explore and optimize the deposition process of perovskite in mesoscopic structure.

Metal halide perovskite (MHP)‐based tandem solar cells, including MHP/silicon, MHP/CuInGa, MHP/organic photovoltaic, MHP/quantum dot, and all‐perovskite tandem cells, which are boosting the development of cost‐effective and high‐performance, next‐generation solar cells than can compete with fossil fuels, are reviewed.

Abstract

Metal halide perovskite (MHP)‐based tandem solar cells are a promising candidate for use in cost‐effective and high‐performance solar cells that can compete with fossil fuels. To understand the research trends for MHP‐based tandem solar cells, a general introduction to single‐junction and multiple‐junction MHP solar cells and the configuration of tandem devices is provided, along with an overview of the recent progress regarding various MHP‐based tandem cells, including MHP/crystalline silicon, MHP/CuInGaS, MHP/organic photovoltaic, MHP/quantum dot, and all‐perovskite tandem cell. Future research directions for MHP‐based tandem solar cells are also discussed.

The whole crystallization pathways and mechanism of two‐step fabricated perovskites are unveiled by in situ grazing‐incidence wide‐angle X‐ray scattering measurements and density functional theory calculations. Sequential A‐site doping of Cs⁺ and GA⁺ is found to alter the crystallization kinetics and improves the perovskite film morphology, giving rise to device efficiency as high as 23.5%.

Abstract

Two‐step‐fabricated FAPbI₃‐based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI₃‐based perovskite film with sequential A‐site doping of Cs⁺ and GA⁺ is revealed by in situ X‐ray scattering and first‐principles calculations. Incorporating Cs⁺ in the first step induces an alternative pathway from δ‐CsPbI₃ to perovskite α‐phase, which is energetically more favorable than the conventional pathways from PbI₂. However, pinholes are formed due to the nonuniform nucleation with sparse δ‐CsPbI₃ crystals. Fortunately, incorporating GA⁺ in the second step can not only promote the phase transition from δ‐CsPbI₃ to the perovskite α‐phase, but also eliminate pinholes via Ostwald ripening and enhanced grain boundary migration, thus boosting efficiencies of perovskite solar cells over 23%. This work demonstrates the unprecedented advantage of the two‐step process over the one‐step process, allowing a precise control of the perovskite crystallization kinetics by decoupling the crystal nucleation and growth process.

Antisolvent engineering is employed to tune the crystal nucleation and grain growth of perovskite for achieving efficient perovskite solar cells. The engineering of perovskites treated with the green antisolvent MABr‐Eth, suppressing defects‐induced nonradiative recombination in perovskite solar cells, is developed. As expected, the device delivers over 21% power conversion efficiency and a better storage and light‐soaking stability.

Abstract

Organic–inorganic hybrid perovskites have attracted considerable attention due to their superior optoelectronic properties. Traditional one‐step solution‐processed perovskites often suffer from defects‐induced nonradiative recombination, which significantly hinders the improvement of device performance. Herein, treatment with green antisolvents for achieving high‐quality perovskite films is reported. Compared to defects‐filled ones, perovskite films by antisolvent treatment using methylamine bromide (MABr) in ethanol (MABr‐Eth) not only enhances the resultant perovskite crystallinity with large grain size, but also passivates the surface defects. In this case, the engineering of MABr‐Eth‐treated perovskites suppressing defects‐induced nonradiative recombination in perovskite solar cells (PSCs) is demonstrated. As a result, the fabricated inverted planar heterojunction device of ITO/PTAA/Cs_0.15FA_0.85PbI₃/PC₆₁BM/Phen‐NADPO/Ag exhibits the best power conversion efficiency of 21.53%. Furthermore, the corresponding PSCs possess a better storage and light‐soaking stability.

Research on flexible mobile energy‐supply devices will promote the development of the Internet of Things. An embedded metal nickel (Ni)‐mesh transparent conductive electrode is used as a flexible substrate for perovskite solar cells (PSCs). These Ni‐mesh‐based PSCs exhibit excellent electric properties and remarkable environmental and mechanical stability.

Abstract

The rapid development of Internet of Things mobile terminals has accelerated the market's demand for portable mobile power supplies and flexible wearable devices. Here, an embedded metal‐mesh transparent conductive electrode (TCE) is prepared on poly(ethylene terephthalate) (PET) using a novel selective electrodeposition process combined with inverted film‐processing methods. This embedded nickel (Ni)‐mesh flexible TCE shows excellent photoelectric performance (sheet resistance of ≈0.2–0.5 Ω sq⁻¹ at high transmittance of ≈85–87%) and mechanical durability. The PET/Ni‐mesh/polymer poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS PH1000) hybrid electrode is used as a transparent electrode for perovskite solar cells (PSCs), which exhibit excellent electric properties and remarkable environmental and mechanical stability. A power conversion efficiency of 17.3% is obtained, which is the highest efficiency for a PSC based on flexible transparent metal electrodes to date. For perovskite crystals that require harsh growth conditions, their mechanical stability and environmental stability on flexible transparent embedded metal substrates are studied and improved. The resulting flexible device retains 76% of the original efficiency after 2000 bending cycles. The results of this work provide a step improvement in flexible PSCs.

A biological polymer is employed to regulate the arrangement of SnO₂ nanocrystals on a substrate and induce vertical crystal growth of a perovskite layer on top. The enhanced interface contact between the electron transport layer and the perovskite layer significantly contributes to the improvement of efficiency and stability of derived planar perovskite solar cells.

Abstract

Perovskite solar cells (PSCs) have rapidly developed and achieved power conversion efficiencies of over 20% with diverse technical routes. Particularly, planar‐structured PSCs can be fabricated with low‐temperature (≤150 °C) solution‐based processes, which is energy efficient and compatible with flexible substrates. Here, the efficiency and stability of planar PSCs are enhanced by improving the interface contact between the SnO₂ electron‐transport layer (ETL) and the perovskite layer. A biological polymer (heparin potassium, HP) is introduced to regulate the arrangement of SnO₂ nanocrystals, and induce vertically aligned crystal growth of perovskites on top. Correspondingly, SnO₂–HP‐based devices can demonstrate an average efficiency of 23.03% on rigid substrates with enhanced open‐circuit voltage (V _OC) of 1.162 V and high reproducibility. Attributed to the strengthened interface binding, the devices obtain high operational stability, retaining 97% of their initial performance (power conversion efficiency, PCE > 22%) after 1000 h operation at their maximum power point under 1 sun illumination. Besides, the HP‐modified SnO₂ ETL exhibits promising potential for application in flexible and large‐area devices.

A narrow‐bandgap polymer acceptor L14 with an acceptor–acceptor (A–A) backbone is synthesized, showing lower‐lying frontier molecular orbitals, higher electron mobility, and larger absorption coefficient without sacrificing photovoltage compared to its donor–acceptor (D–A) analog polymer, L11. When applied in all‐polymer solar cells, L14 yields an outstanding efficiency of 14.3%.

Abstract

Narrow‐bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow‐bandgap polymer acceptor L14, featuring an acceptor–acceptor (A–A) type backbone, is synthesized by copolymerizing a dibrominated fused‐ring electron acceptor (FREA) with distannylated bithiophene imide. Combining the advantages of both the FREA and the A–A polymer, L14 not only shows a narrow bandgap and high absorption coefficient, but also low‐lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved electron transfer character, but unexpectedly, without sacrificing open‐circuit voltage (V _oc), which is attributed to a small nonradiative recombination loss (E _loss,nr) of 0.22 eV. Benefiting from the improved photocurrent along with the high fill factor and V _oc, an excellent efficiency of 14.3% is achieved, which is among the highest values for all‐polymer solar cells (all‐PSCs). The results demonstrate the superiority of narrow‐bandgap A–A type polymers for improving all‐PSC performance and pave a way toward developing high‐performance polymer acceptors for all‐PSCs.

The recent progress of CsPbI₃ perovskite for highly efficient and stable photovoltaics are summarized. Furthermore, those important phase stabilization strategies for the black phase CsPbI₃ are also discussed. With the advancing of fundamental study on CsPbI₃ perovskite material properties, the CsPbI₃ perovskite and other inorganic perovskite will become more and more promising for high‐efficiency and stable perovskites solar cells.

Abstract

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high‐efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI₃ with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single‐junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI₃ exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI₃ induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI₃ perovskite are presented. The development of various solution chemistry approaches for depositing high‐quality phase‐pure CsPbI₃ perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI₃ are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI₃ have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI₃ materials will further advance inorganic perovskite for highly stable and efficient photovoltaics.

In tandem organic photovoltaics, most ultraviolet–visible photons are absorbed by the front sub‐cell, so in the rear sub‐cell, excitons generated on large‐bandgap donors will be reduced significantly. This reduces the conductivity and limits the hole‐transporting property of the rear sub‐cell. An infrared‐absorbing polymer donor is introduced, which provides a second hole‐generation/transporting mechanism to minimize the aforementioned detrimental effects.

Abstract

In tandem organic photovoltaics, the front subcell is based on large‐bandgap materials, whereas the case of the rear subcell is more complicated. The rear subcell is generally composed of a narrow‐bandgap acceptor for infrared absorption but a large‐bandgap donor to realize a high open‐circuit voltage. Unfortunately, most of the ultraviolet–visible part of the photons are absorbed by the front subcell; as a result, in the rear subcell, the number of excitons generated on large‐bandgap donors will be reduced significantly. This reduces the (photo) conductivity and finally limits the hole‐transporting property of the rear subcell. In this work, a simple and effective way is proposed to resolve this critical issue. To ensure sufficient photogenerated holes in the rear subcell, a small amount of an infrared‐absorbing polymer donor as a third component is introduced, which provides a second hole‐generation and transporting mechanism to minimize the aforementioned detrimental effects. Finally, the short‐circuit current density of the two‐terminal tandem organic photovoltaic is significantly enhanced from 10.3 to 11.7 mA cm⁻² (while retaining the open‐circuit voltage and fill factor) to result in an enhanced power conversion efficiency of 15.1%.

Research on flexible mobile energy‐supply devices will promote the development of the Internet of Things. An embedded metal nickel (Ni)‐mesh transparent conductive electrode is used as a flexible substrate for perovskite solar cells (PSCs). These Ni‐mesh‐based PSCs exhibit excellent electric properties and remarkable environmental and mechanical stability.

Abstract

The rapid development of Internet of Things mobile terminals has accelerated the market's demand for portable mobile power supplies and flexible wearable devices. Here, an embedded metal‐mesh transparent conductive electrode (TCE) is prepared on poly(ethylene terephthalate) (PET) using a novel selective electrodeposition process combined with inverted film‐processing methods. This embedded nickel (Ni)‐mesh flexible TCE shows excellent photoelectric performance (sheet resistance of ≈0.2–0.5 Ω sq⁻¹ at high transmittance of ≈85–87%) and mechanical durability. The PET/Ni‐mesh/polymer poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS PH1000) hybrid electrode is used as a transparent electrode for perovskite solar cells (PSCs), which exhibit excellent electric properties and remarkable environmental and mechanical stability. A power conversion efficiency of 17.3% is obtained, which is the highest efficiency for a PSC based on flexible transparent metal electrodes to date. For perovskite crystals that require harsh growth conditions, their mechanical stability and environmental stability on flexible transparent embedded metal substrates are studied and improved. The resulting flexible device retains 76% of the original efficiency after 2000 bending cycles. The results of this work provide a step improvement in flexible PSCs.

A biological polymer is employed to regulate the arrangement of SnO₂ nanocrystals on a substrate and induce vertical crystal growth of a perovskite layer on top. The enhanced interface contact between the electron transport layer and the perovskite layer significantly contributes to the improvement of efficiency and stability of derived planar perovskite solar cells.

Abstract

Perovskite solar cells (PSCs) have rapidly developed and achieved power conversion efficiencies of over 20% with diverse technical routes. Particularly, planar‐structured PSCs can be fabricated with low‐temperature (≤150 °C) solution‐based processes, which is energy efficient and compatible with flexible substrates. Here, the efficiency and stability of planar PSCs are enhanced by improving the interface contact between the SnO₂ electron‐transport layer (ETL) and the perovskite layer. A biological polymer (heparin potassium, HP) is introduced to regulate the arrangement of SnO₂ nanocrystals, and induce vertically aligned crystal growth of perovskites on top. Correspondingly, SnO₂–HP‐based devices can demonstrate an average efficiency of 23.03% on rigid substrates with enhanced open‐circuit voltage (V _OC) of 1.162 V and high reproducibility. Attributed to the strengthened interface binding, the devices obtain high operational stability, retaining 97% of their initial performance (power conversion efficiency, PCE > 22%) after 1000 h operation at their maximum power point under 1 sun illumination. Besides, the HP‐modified SnO₂ ETL exhibits promising potential for application in flexible and large‐area devices.

A narrow‐bandgap polymer acceptor L14 with an acceptor–acceptor (A–A) backbone is synthesized, showing lower‐lying frontier molecular orbitals, higher electron mobility, and larger absorption coefficient without sacrificing photovoltage compared to its donor–acceptor (D–A) analog polymer, L11. When applied in all‐polymer solar cells, L14 yields an outstanding efficiency of 14.3%.

Abstract

Narrow‐bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow‐bandgap polymer acceptor L14, featuring an acceptor–acceptor (A–A) type backbone, is synthesized by copolymerizing a dibrominated fused‐ring electron acceptor (FREA) with distannylated bithiophene imide. Combining the advantages of both the FREA and the A–A polymer, L14 not only shows a narrow bandgap and high absorption coefficient, but also low‐lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved electron transfer character, but unexpectedly, without sacrificing open‐circuit voltage (V _oc), which is attributed to a small nonradiative recombination loss (E _loss,nr) of 0.22 eV. Benefiting from the improved photocurrent along with the high fill factor and V _oc, an excellent efficiency of 14.3% is achieved, which is among the highest values for all‐polymer solar cells (all‐PSCs). The results demonstrate the superiority of narrow‐bandgap A–A type polymers for improving all‐PSC performance and pave a way toward developing high‐performance polymer acceptors for all‐PSCs.

The recent progress of CsPbI₃ perovskite for highly efficient and stable photovoltaics is summarized. Furthermore, those important phase stabilization strategies for black‐phase CsPbI₃ are also discussed. With the advancing of fundamental studies on CsPbI₃ perovskite material properties, the CsPbI₃ perovskite and other inorganic perovskites will become more and more promising for high‐efficiency and stable perovskite solar cells.

Abstract

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high‐efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI₃ with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single‐junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI₃ exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI₃ induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI₃ perovskite are presented. The development of various solution chemistry approaches for depositing high‐quality phase‐pure CsPbI₃ perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI₃ are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI₃ have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI₃ materials will further advance inorganic perovskite for highly stable and efficient photovoltaics.

Metal halide perovskite nanorods show strong polarized emission, high optical gain, and improved charge transport, and thus hold promising applications in solar cells, light‐emitting diodes (LEDs), photodetectors, photodetectors/phototransistors, and lasers. Recent advances in the synthetic strategies, growth mechanism, and optical and electronic properties of these materials are discussed, and the emerging applications are highlighted.

Abstract

Quasi‐1D metal halide perovskite nanorods (NRs) are emerging as a type of materials with remarkable optical and electronic properties. Research into this field is rapidly expanding and growing in the past several years, with significant advances in both mechanistic studies of their growth and widespread possible applications. Here, the recent advances in 1D metal halide perovskite nanocrystals (NCs) are reviewed, with a particular emphasis on NRs. At first, the crystal structures of perovskites are elaborated, which is followed by a review of the major synthetic approaches toward perovskite NRs, such as wet‐chemical synthesis, substrate‐assisted growth, and anion exchange reactions, and discussion of the growth mechanisms associated with each synthetic method. Then, thermal and aqueous stability and the linear polarized luminescence of perovskite NRs are considered, followed by highlighting their applications in solar cells, light‐emitting diodes, photodetectors/phototransistors, and lasers. Finally, challenges and future opportunities in this rapidly developing research area are summarized.