awn

A new series of dopant‐free hole‐transporting materials (HTMs) YZT1–YZT4 featuring porphyrin backbone is achieved in which the best power conversion efficiency (PCE) of YZT4 is 14.95% for doped and that of YZT1 is 13.10% for dopant‐free perovskite solar cells (PSCs) based on TiO₂ semiconductors.

A new series of structurally simple and easily accessible hole‐transporting materials (HTMs) YZT1–YZT4 using porphyrin backbone is devised for high‐performance perovskite solar cells (PSCs) with and without the aid of doping. The YZT‐series HTMs have either push–push or push–pull type planar linear molecular geometry with substitution of linear or branched alkylamine. UV–vis absorption, photoluminance (PL) quenching experiments, and theoretical studies all suggest a different pattern of molecular packing induced by molecular geometry and/or substituted chains. Nonetheless, both types of porphyrin HTMs perform well in TiO₂‐based PSCs when doped YZT4 with a power conversion efficiency (PCE) of 14.95% and undoped YZT1 with a PCE of 13.10%. The results clearly reveal the potential for porphyrin‐based HTMs for use in dopant‐free PSCs.

1,3‐dimethyl‐2‐(thiophen‐2‐yl)‐2,3‐dihydro‐1H‐benzo[d]imidazole (DMBI‐2‐Th) and its iodine ionized molecule DMBI‐2‐Th‐I are developed to regulate the electronic states of bulk perovskite for efficient p–i–n pero‐SCs, leading to a significant improvement in electron trap density, electron concentration, ambipolar charge transporting property, and electronic extraction efficiency. Finally, a promising power conversion efficiency of 20.90% with excellent moisture stability is obtained.

Abstract

The power conversion efficiency (PCE) of planar p–i–n perovskite solar cells (pero‐SCs) is commonly lower than that of the n–i–p pero‐SCs, due to the severe nonradiative recombination stemming from the more p‐type perovskite with prevailing electron traps. Here, two n‐type organic molecules, DMBI‐2‐Th and DMBI‐2‐Th‐I, with hydrogen‐transfer properties for the doping of bulk perovskite aimed at regulating its electronic states are synthesized. The generated radicals in these n‐type dopants with high‐lying singly occupied molecular orbitals enable easy transfer of the thermally activated electrons to the MAPbI₃ perovskite for the realization of n‐doped perovskites. The n‐doping degree could be further enhanced by using the iodine ionized dopant DMBI‐2‐Th‐I. The doping effect could reduce the electron trap density, increase the electron concentration of the bulk perovskite, and simultaneously improve the surface electronic contact. When the DMBI‐2‐Th‐I‐doped perovskite is used in planar p–i–n pero‐SCs, the nonradiative recombination is significantly suppressed. As a result, the photovoltaic performance improved significantly, as evidenced by an excellent PCE of 20.90% and a robust ambient stability even under high relative humidity. To the best of the knowledge, this work represents the first example where organic n‐type dopants are used to tune the electronic states of a bulk perovskite film for efficient planar p–i–n pero‐SCs.

The temperature dependence of the local and long‐range structures of the halide perovskite CsPbI₃ is studied. The Cs atom splits between two sites with the second site having a lower effective coordination number, suggesting that Cs rattles within the structure. Rattling, few CsI contacts, and the high degree of octahedral distortion explain the thermodynamic instability of perovskite‐phase CsPbI₃ .

Abstract

Despite the tremendous interest in halide perovskite solar cells, the structural reasons that cause the all‐inorganic perovskite CsPbI₃ to be unstable at room temperature remain mysterious, especially since many tolerance‐factor‐based approaches predict CsPbI₃ should be stable as a perovskite. Here single‐crystal X‐ray diffraction and X‐ray pair distribution function (PDF) measurements characterize bulk perovskite CsPbI₃ from 100 to 295 K to elucidate its thermodynamic instability. While Cs occupies a single site from 100 to 150 K, it splits between two sites from 175 to 295 K with the second site having a lower effective coordination number, which, along with other structural parameters, suggests that Cs rattles in its coordination polyhedron. PDF measurements reveal that on the length scale of the unit cell, the PbI octahedra concurrently become greatly distorted, with one of the IPbI angles approaching 82° compared to the ideal 90°. The rattling of Cs, low number of CsI contacts, and high degree of octahedral distortion cause the instability of perovskite‐phase CsPbI_3. These results reveal the limitations of tolerance factors in predicting perovskite stability and provide detailed structural information that suggests methods to engineer stable CsPbI₃‐based solar cells.

Nanopyramid arrays of 1D highly oriented anatase TiO₂ present an oriented electric field distribution, which is favorable for charge separation and transport. An impressive power conversion efficiency of approximately 22.5 % was achieved, which is the highest efficiency reported for perovskite solar cells consisting of 1D electron transport materials to date.

Abstract

One‐dimensional (1D) nanostructured oxides are proposed as excellent electron transport materials (ETMs) for perovskite solar cells (PSCs); however, experimental evidence is lacking. A facile hydrothermal approach was employed to grow highly oriented anatase TiO₂ nanopyramid arrays and demonstrate their application in PSCs. The oriented TiO₂ nanopyramid arrays afford sufficient contact area for electron extraction and increase light transmission. Moreover, the nanopyramid array/perovskite system exhibits an oriented electric field that can increase charge separation and accelerate charge transport, thereby suppressing charge recombination. The anatase TiO₂ nanopyramid array‐based PSCs deliver a champion power conversion efficiency of approximately 22.5 %, which is the highest power conversion efficiency reported to date for PSCs consisting of 1D ETMs. This work demonstrates that the rational design of 1D ETMs can achieve PSCs that perform as well as typical mesoscopic and planar PSCs.

The nonionic polymer with multiple amino groups is introduced to passivate both metal‐ and halide‐induced defects of all‐inorganic CsPbI₂Br perovskite by coordination and hydrogen bonds, simultaneously. Consequently, a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film are achieved, which boosts the efficiency of perovskite solar cells up to 15.48% with excellent humidity stability.

The all‐inorganic CsPbI₂Br perovskite with superior thermal durability faces challenges of low‐phase stability and high moisture sensitivity. Herein, a nonionic additive of polyethyleneimine (PEI) with multiple amino groups is introduced to form hydrogen bond with I⁻/Br⁻ ions and coordinate with Pb²⁺/Cs⁺ ions simultaneously. The strong interplay between PEI and CsPbI₂Br achieves a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film, which boosts the power conversion efficiency (PCE) of perovskite solar cells to 15.48%. The hydrophobic long alkyl chain of PEI greatly improves the humidity resistance, retaining 81.9% of initial PCE of zjr unsealed device under 20 ± 5% relative humidity (RH) for 500 h. Remarkably, a PCE of 13.37% is achieved by the device based on CsPbI₂Br–PEI film processed under ambient condition (≈22% RH, ≈25 °C).

A synthetic polyhalide ligand (2‐picolyl)amine triiodide as a molecular glue is used to passivate halide vacancies at grain boundaries directionally and throughout grain bulk of perovskites. The inverted perovskite solar cells after passivation are allowed to be more efficient, and are profoundly stabilized in both ambient air and light‐soaking circumstances.

The fundamental instability of hybrid perovskite solar cells originates from the considerable halide vacancies. Furthermore, the local roles of halide vacancies between grain boundaries and grain bulk generally conflict, thus inhibiting complete passivation. To overcome this obstacle, a rational polyhalide ligand, di‐(2‐picolyl)amine triiodide, is designed as a molecular “glue” to achieve comprehensive passivation. Unlike a monohalide ligand, this ligand has multiple iodide ions and a quasiplanar tridentate chelation capability, contributing to directional passivation along the grain boundaries and overall passivation throughout the grain bulk. Using this molecular glue passivation, the best inverted solar cell yields an efficiency of 20.02%. Moreover, the relative stability of this cell in ambient air (≈40% humidity, 800 h aging) and under light‐soaking conditions (500 h aging) is profoundly enhanced by 33.33% and 22.26%, respectively. Herein, important insights into the design of passivating molecules to achieve low‐defect perovskites toward the development of multifunctional devices are provided.

A formamidinium (FA)‐based quasi‐2D Ruddlesden–Popper (RP) perovskite, namely, (ThMA)₂(FA) _{n −1}Pb _n I_{3 n +1} (nominal n = 5), is successfully demonstrated with high photovoltaic performance by using an organic‐salt‐assisted crystal growth method. The optimized device exhibits a champion efficiency of 19.06%, which is a record for quasi‐2D RP perovskite solar cells with nominal n‐value lower than 6.

Abstract

Quasi‐2D Ruddlesden–Popper (RP) perovskite solar cells (PSCs) have drawn significant attention due to their appealing environmental stability compared to their 3D counterparts. However, the relatively low power conversion efficiency (PCE) greatly limits their applications. Here, high photovoltaic performance is demonstrated for quasi‐2D RP PSCs using 2‐thiophenemethylammonium as spacer with nominal n‐value of 5, which is based on the stoichiometry of the precursors. The incorporation of formamidinium (FA) in quasi‐2D RP perovskites reduces the bandgap and improves the light absorption ability, resulting in enlarged photocurrent and an increased PCE of 16.18%, which is higher than that of reported analogous methylammonium (MA)‐based quasi‐2D PSC (≈15%). A record high PCE of 19.06% is further demonstrated by using an organic salt, namely, 4‐(trifluoromethyl)benzylammonium iodide, assisted crystal growth (OACG) technique, which can induce the crystal growth and orientation, tune the surface energy levels, and suppress the charge recombination losses. More importantly, the devices based on OACG‐processed quasi‐2D RP perovskites show remarkable environmental stability and thermal stability, for example, the PCE retaining ≈96% of its initial value after storage at 80 °C for 576 h, while only ≈37% of the original efficiency left for FAPbI₃‐based

3D PSCs.

Publication date: 15 July 2020

Source: Joule, Volume 4, Issue 7

Author(s): Qin Hu, Wei Chen, Wenqiang Yang, Yu Li, Yecheng Zhou, Bryon W. Larson, Justin C. Johnson, Yi-Hsien Lu, Wenkai Zhong, Jinqiu Xu, Liana Klivansky, Cheng Wang, Miquel Salmeron, Aleksandra B. Djurišić, Feng Liu, Zhubing He, Rui Zhu, Thomas P. Russell

Publication date: 15 July 2020

Source: Joule, Volume 4, Issue 7

Author(s): Xu Chen, Ziyan Jia, Zeng Chen, Tingming Jiang, Lizhong Bai, Feng Tao, Jianwu Chen, Xinya Chen, Tianyu Liu, Xuehui Xu, Chenying Yang, Weidong Shen, Wei E.I. Sha, Haiming Zhu, Yang (Michael) Yang

This work reports a compatible strategy to enhance the efficiency of planar n–i–p Sb₂Se₃ solar cells through Sb₂Se₃ surface modification and an architecture with oriented 1D van der Waals material, trigonal selenium (t‐Se). The p‐type t‐Se layer functionally works as a surface passivation and hole transport material. The all‐inorganic device structure enables high efficiency and superb stability.

Abstract

Environmentally benign and potentially cost‐effective Sb₂Se₃ solar cells have drawn much attention by continuously achieving new efficiency records. This article reports a compatible strategy to enhance the efficiency of planar n–i–p Sb₂Se₃ solar cells through Sb₂Se₃ surface modification and an architecture with oriented 1D van der Waals material, trigonal selenium (t‐Se). A seed layer assisted successive close spaced sublimation (CSS) is developed to fabricate highly crystalline Sb₂Se₃ absorbers. It is found that the Sb₂Se₃ absorber exhibits a Se‐deficient surface and negative surface band bending. Reactive Se is innovatively introduced to compensate the surface Se deficiency and form an (101) oriented 1D t‐Se interlayer. The p‐type t‐Se layer promotes a favored band alignment and band bending at the Sb₂Se₃/t‐Se interface, and functionally works as a surface passivation and hole transport material, which significantly suppresses interface recombination and enhances carrier extraction efficiency. An efficiency of 7.45% is obtained in a planar Sb₂Se₃ solar cell in superstrate n–i–p configuration, which is the highest efficiency for planar Sb₂Se₃ solar cells prepared by CSS. The all‐inorganic Sb₂Se₃ solar cell with t‐Se shows superb stability, retaining ≈98% of the initial efficiency after 40 days storage in open air without encapsulation.

A composite consisting of 1D cation‐doped TiO₂ brookite nanorod embedded by 0D fullerene is investigated as a top modification buffer for inverted perovskite photovoltaic (IP‐PV) cells. The resultant IP‐PV displays an efficiency exceeding 22% with a favorable stability. This work opens up more opportunities in expanding the material inventory for charge transfer layer in perovskite solar cells development and application.

Abstract

Simultaneously achieving high efficiency and high durability in perovskite solar cells is a critical step toward the commercialization of this technology. Inverted perovskite photovoltaic (IP‐PV) cells incorporating robust and low levelized‐cost‐of‐energy (LCOE) buffer layers are supposed to be a promising solution to this target. However, insufficient inventory of materials for back‐electrode buffers substantially limits the development of IP‐PV. Herein, a composite consisting of 1D cation‐doped TiO₂ brookite nanorod (NR) embedded by 0D fullerene is investigated as a top modification buffer for IP‐PV. The cathode buffer is constructed by introducing fullerene to fill the interstitial space of the TiO₂ NR matrix. Meanwhile, cations of transition metal Co or Fe are doped into the TiO₂ NR to further tune the electronic property. Such a top buffer exhibits multifold advantages, including improved film uniformity, enhanced electron extraction and transfer ability, better energy level matching with perovskite, and stronger moisture resistance. Correspondingly, the resultant IP‐PV displays an efficiency exceeding 22% with a 22‐fold prolonged working lifetime. The strategy not only provides an essential addition to the material inventory for top electron buffers by introducing the 0D:1D composite concept, but also opens a new avenue to optimize perovskite PVs with desirable properties.

Trial separation : 2D layered Pb‐ and Sn‐halide perovskites show surprising optical properties, such as dual excitonic emissions. Such unusual properties are shown to arise through to the interaction between the 2D inorganic layers. Separating the inorganic layers either by molecular intercalation or by increasing the length organic spacer ion reversibly switches the optical properties.

Abstract

In layered hybrid perovskites, such as (BA)₂PbI₄ (BA=C₄H₉NH₃), electrons and holes are considered to be confined in atomically thin two dimensional (2D) Pb–I inorganic layers. These inorganic layers are electronically isolated from each other in the third dimension by the insulating organic layers. Herein we report our experimental findings that suggest the presence of electronic interaction between the inorganic layers in some parts of the single crystals. The extent of this interaction is reversibly tuned by intercalation of organic and inorganic molecules in the layered perovskite single crystals. Consequently, optical absorption and emission properties switch reversibly with intercalation. Furthermore, increasing the distance between inorganic layers by increasing the length of the organic spacer cations systematically decreases these electronic interactions. This finding that the parts of the layered hybrid perovskites are not strictly electronically 2D is critical for understanding the electronic, optical, and optoelectronic properties of these technologically important materials.

SnO₂ and perovskite have been bridged with multifunctional graphdiyne. Such delicate interface modification boosted the performance of solar cells in energy band alignment, electron mobility improvement, controllable perovskite growth inducement, and interface defect passivation.

Abstract

The matching of charge transport layer and photoactive layer is critical in solar energy conversion devices, especially for planar perovskite solar cells based on the SnO₂ electron‐transfer layer (ETL) owing to its unmatched photogenerated electron and hole extraction rates. Graphdiyne (GDY) with multi‐roles has been incorporated to maximize the matching between SnO₂ and perovskite regarding electron extraction rate optimization and interface engineering towards both perovskite crystallization process and subsequent photovoltaic service duration. The GDY doped SnO₂ layer has fourfold improved electron mobility due to freshly formed C−O σ bond and more facilitated band alignment. The enhanced hydrophobicity inhibits heterogeneous perovskite nucleation, contributing to a high‐quality film with diminished grain boundaries and lower defect density. Also, the interfacial passivation of Pb−I anti‐site defects has been demonstrated via GDY introduction.

The article studies SnO₂'s role in the stability of air‐processed planar perovskite solar cells. UV treatment of sub‐cells (500 h N₂ environment) speeds up the depletion of perovskite films, leading to excess PbI₂ formation at the perovskite surfaces. This inadvertently leads to full device stabilization through passivation as seen in maximum power point (MPP) measurements of perovskite solar cells incorporating UV‐treated sub‐cells.

SnO₂ is nowadays the widely preferred material as an electron transport layer (ETL) in most n‐i‐p planar perovskite solar cells (PSCs) due to its facility for ambient, low temperature processing, and ultraviolet (UV) stability. Most reports published so far study device stability on full cells. Herein, the role of slot‐die‐coated SnO₂ on air‐processed planar PSCs by analyzing sub‐cells (indium tin oxide [ITO]/SnO₂/perovskite) under UV exposure is investigated. Results from UV–vis spectroscopy, depth profiling using X‐ray diffraction measurement in grazing incidence mode (GIXRD), X‐ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy measurements show that UV treatment of ITO/SnO₂/perovskite leads to a reduced electron transfer to the SnO₂ layer and a gradual increase in the amount of PbI₂ toward the perovskite surfaces. Subsequently, hole transport layer (HTL) and electrodes are applied on SnO₂/perovskite interfaces (UV‐treated and non‐UV‐treated) and complete devices are fabricated. Device performance is compared and analyzed through J–V curves and maximum power point (MPP) tracking. Results show that devices built on a UV‐treated SnO₂/perovskite interface show better stability attributed to the presence of excess PbI₂ resulting in a passivation effect. Challenges in uniform film formation of slot‐die‐coated SnO₂ and potential solutions using a polymeric additive are also highlighted.

An optimal power conversion efficiency (PCE) of 17.4% is achieved in the optimized ternary organic photovoltaics (OPVs) with two well‐compatible acceptors (BTP‐4F‐12 and MeIC) and one wide bandgap donor (PM6), resulting from simultaneously improved J _SC, fill factor (FF), and V _OC. The energy loss of ternary OPVs is minimized compared with the two binary OPVs, which is an important development for PCE improvement of ternary OPVs.

Abstract

A power conversion efficiency (PCE) of 16.2% is achieved in PM6:BTP‐4F‐12 based organic photovoltaics (OPVs). On the basis of efficient binary OPVs, a series of ternary OPVs are constructed by incorporating MeIC as the third component. The open circuit voltages (V _OCs) of ternary OPVs can be gradually increased along with the incorporation of MeIC, suggesting the formation of an alloy state between BTP‐4F‐12 and MeIC with good compatibility. The energy loss (E _loss) of ternary OPVs can be decreased compared with that of two binary OPVs, contributing to the V _OC improvement of ternary OPVs. The short circuit current density (J _SC) and fill factor (FF) of ternary OPVs can also be simultaneously enhanced with MeIC content up to 10 wt% in acceptors, leading to 17.4% PCE of the optimized ternary OPVs. The J _SC and FF improvement of ternary OPVs is thought to result from the optimized ternary active layers with more efficient photon harvesting, exciton dissociation and charge transport. The 17.4% PCE and 79.2% FF is among the top values of ternary OPVs. This work indicates that a ternary strategy is an emerging method to simultaneously minimize E _loss and optimize photon harvesting as well as improve the morphology of active layers for realizing performance improvement for OPVs.

A comprehensive review on the current development and advanced understanding of Sn‐based perovskite solar cell (PSCs) from the viewpoint of A‐site cation engineering is demonstrated. The key challenges and current opportunities in the field of Sn‐based PSCs are discussed. This review highlights the significant promise of Sn‐based metal halide perovskites in the application of PSCs as well as many other potential opotoelectronic devices.

Abstract

Pb‐based metal halide perovskites (MHPs) have emerged as efficient light absorbers in third‐generation photovoltaic devices, and the latest certified power conversion efficiency (PCE) of Pb‐based perovskite solar cells (PSCs) has reached 25.2%. Despite great progress, Pb‐based MHPs are affected by toxicity, which hinders their market entry in a potential future large‐scale commercialization effort. Therefore, the exploration of Pb‐free MHPs has become one of the alternative solutions sought in the community. Among all the Pb‐free MHPs, Sn‐based MHPs show great promise owing to their similar or even superior theoretical optoelectronic characteristics. After several years of development, the PCE of Sn‐based PSCs has recently been approaching 10%, with the breakthroughs mainly coming from A‐site cation engineering of Sn‐based MHPs. In this review, the crucial status of A‐site cation engineering strategies in the research of Sn‐based PSCs is highlighted. First, the way the features of A‐site cation influence the structure and characteristics of MHPs is systematically demonstrated. Then, the state‐of‐the‐art developments, focusing on A‐site cation engineering of Sn‐based MHPs, are comprehensively reviewed. Subsequently, the current challenges and opportunities for further boosting the performance of Sn‐based PSCs are discussed. Finally, conclusions and perspectives on the promising Sn‐based optoelectronic devices are discussed.

An aryl diammonium iodide: PDMAI is demonstrated first to be highly promising to enhance open‐circuit voltage, short‐circuit current, and stability of FAMAPbI₃ based perovskite solar cells through surface passivation. Theoretical calculation suggests a stronger energy binding between PDMAI and perovskite surface. This work provides a new passivation strategy for efficient and stable perovskite solar cells.

Abstract

Surface passivation is increasingly one of the most prominent strategies to promote the efficiency and stability of perovskite solar cells (PSCs). However, most passivation molecules hinder carrier extraction due to poorly conductive aggregation between perovskite surface and carrier transportation layer. Herein, a novel molecule: p‐phenyl dimethylammonium iodide (PDMAI) with ammonium group on both terminals is introduced, and its passivation effect is systematically investigated. It is found that PDMAI can mitigate defects at the surface and promote carrier extraction from perovskite to the hole transporting layer, leading to a lift of open‐circuit voltage of 40 mV. Profiting from superior PDMAI passivation, the average efficiency of PSCs has been elevated from 19.69% to 20.99%. As demonstrated with density functional theory calculations, PDMAI probably tends to anchor onto the perovskite surface with both NH₃I tails, and enhances the adhesion and contact to perovskite layer. The exposed hydrophobic aryl core protects perovskite against detrimental environmental factors. In addition, the alkyl component between aryl and ammonium groups is demonstrated to be essentially vital in triggering passivation function, which offers the guidance for the design of passivation molecules.

When introduced beneath the 3D perovskite layer, the 2D perovskite seeding layer acts as a template for growth in the planar direction, resulting in an increase in perovskite grains with less and narrow grain boundaries. As a result, the hydrophobicity of the film increases resulting in better stability and improved efficiency when the films are processed in air.

Abstract

Despite the record power conversion efficiencies, inverted perovskite solar cells (PSCs) are still looking to overcome the challenge of moisture instability. This is mitigated by introducing 2D perovskite at the base of a 3D perovskite via coating of ethylenediamine bications on top of the hole transport layer of p–i–n planar configured devices. The cations induce thin 2D perovskite growth beneath the 3D perovskite to create a 2D/3D hybrid active layer. This 2D layer in turn acts as a template for the growth of relatively large grains compared to that of pure 3D perovskite films. This stems from the merging of grain boundaries. The hydrophobicity of the 2D/3D perovskite film consequently improves, as evidenced by a large contact angle of 93.1°, compared to 68.9° for the 3D perovskite film. Because there are fewer defects sourced from grain boundaries, the air‐processed 2D/3D perovskite devices yield a high power conversion efficiency of 15.02%, compared to 13.10% from 3D perovskite devices. When stored in moderately humid environment of 55% relative humidity, the 2D/3D devices exhibit longer stabilities, with 75% of their power conversion efficiencies maintained after 150 h, compared to a total loss in efficiency for 3D device in the same time frame.

High‐performance semitransparent organic solar cells are achieved through the combined design efforts on the formulation of near‐infrared ternary blends and optical control over photonic reflectors, which exhibit excellent features of power generation, they being see‐through, and infrared reflection.

Abstract

Clean energy production and saving play vital impacts on the sustainability of the global community. Herein, high‐performance semitransparent organic solar cells (ST‐OSCs) with excellent features of power generation, being see‐through, and infrared reflection of heat dissipation, with promising perspectives for building‐integrated photovoltaics (BIPVs) are reported. To simultaneously improve average visible transmittance (AVT) and power conversion efficiency (PCE), formally in a trade‐off relationship, of ST‐OSCs, new ternary blends with alloy‐like near‐infrared (NIR) acceptors are employed, which are effective to improve device efficiency while maintaining visible absorption unchanged, resulting in PCEs of 16.8% for opaque devices and 13.1% for semitransparent OSCs (AVT of 22.4% and infrared photon radiation rejection (IRR) of 77%). Further, multifunctional ST‐OSCs are realized via introducing simple, yet effective photonic reflectors, together with optical simulation, leading to not only perfect fitting of the visible transmittance peak (555 nm) to the photopic response of the human eye but also an excellent IRR of 90% (780–2500 nm), along with 23% AVT and over 12% PCE. This is thought to be the best‐performing multifunctional ST‐OSC with promising prospects as BIPVs in terms of power generation, heat dissipation, and being see‐through.

A gradient grain‐sized (GGS) CsPbI₃ bilayer is developed to stabilize the α phase via a single‐step film‐deposition process. The perovskite solar cell based on the GGS CsPbI₃ bilayer shows an efficiency of 15.5% and operates stably for 1000 h under ambient conditions.

Abstract

The emerging inorganic CsPbI₃ perovskites are promising wide‐bandgap materials for application in tandem solar cells, but they tend to transit from a black α phase to a yellow δ phase in ambient conditions. Herein, a gradient grain‐sized (GGS) CsPbI₃ bilayer is developed to stabilize the α phase via a single‐step film deposition process. The spontaneously upward migration of (adamantan‐1‐yl)methanammonium (ADMA) based on the hot‐casting technique causes self‐assembly of the hierarchical morphology for the perovskite layers. Due to the strong steric effect of the surficial ADMA cation, a self‐assembly tiny grain‐sized CsPbI₃ layer is in situ formed at the surface site, which exhibits notably enhanced phase stability by its high surface energy. Meanwhile, a large grain‐sized CsPbI₃ layer is obtained at the bottom site with high charge mobility and low trap density of states, which benefits from the regulated growth rates by the interaction between ADMA and perovskites. The perovskite solar cell (PSC) based on the GGS CsPbI₃ bilayer shows an efficiency of 15.5% and operates stably for 1000 h under ambient conditions. This work confirms that redistributing the surface energy of perovskite films is a facile strategy to stabilize metastable PSCs without the cost of efficiency loss.

Di‐n‐propylamine solution in methyl acetate is successfully demonstrated as an efficient solid‐state treatment for CsPbI₃ perovskite quantum dot (PQD) solar cells, and a record power conversion efficiency of ≈15% and high reproducibility are achieved for CsPbI₃ PQD solar cells.

Abstract

Lead‐halide perovskite quantum dots (PQDs) or more broadly, nanocrystals possess advantageous features for solution‐processed photovoltaic devices. The nanocrystal surface ligands play a crucial role in the transport of photogenerated carriers and ultimately affect the overall performance of PQD solar cells. Significantly improved CsPbI₃ PQD synthetic yield and solar‐cell performance through surface ligand management are demonstrated. The treatment of a secondary amine, di‐n‐propylamine (DPA), provides a mild and efficient approach to control the surface ligand density of PQDs, which has an apparently different working mechanism compared to previously reported surface treatments. Using an optimal DPA concentration, the treatment can simultaneously remove both long‐chain insulating surface ligands of oleic acid and oleylamine, even for unpurified PQDs with high ligand density. As a result, the electrical coupling between PQDs is enhanced, leading to improved charge transport, reduced carrier recombination, and a high power conversion efficiency approaching 15% for CsPbI₃‐PQD‐based solar cells. In addition, the production yield of CsPbI₃ PQDs can be increased by a factor of 8. These results highlight the importance of developing new ligand‐management strategies, specifically for emerging PQDs to achieve scalable and high‐performance perovskite‐based optoelectronic devices.

The mechanism of 2D halide perovskite film formation is resolved using in situ grazing‐incidence wide‐angle scattering (GIWAXS). The film begins as a sol–gel precursor before first forming a 3D MAPbI₃‐like phase at the air/liquid interface. This acts as a template for the highly textured 2D phase with the layers perpendicular to the substrate, which grows closer to the substrate.

Abstract

2D hybrid halide perovskites with the formula (A′)₂(A) _{n ‐1}Pb _n I_{3 n +1} have remarkable stability and promising efficiency in photovoltaic and optoelectronic devices, yet fundamental understanding of film formation, key to optimizing these devices, is lacking. Here, in situ grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) is used to monitor film formation during spin‐coating. This elucidates the general film formation mechanism of 2D halide perovskites during one‐step spin‐coating. There are three stages of film formation: sol–gel, oriented 3D, and 2D. Three precursor phases form during the sol–gel stage and transform to perovskite, first giving a highly oriented 3D‐like phase at the air/liquid interface followed by subsequent nucleations forming slightly less oriented 2D perovskite. Furthermore, heating before crystallization leads to fewer nucleations and faster removal of the precursors, improving orientation. This outlines the primary causes of phase distribution and perpendicular orientation in 2D perovskite films and paves the way for rationally designed film fabrication techniques.