Chen Weijie

An underlayer with a bilayer structure of 2,2′,7,7′-tetrakis(N,N-dip-methoxyphenylamine)-9,9′-spirobifluorene and copper phthalocyanine 3,4′,4″,4′″-tetrasulfonated acid tetrasodium salt is applied to inverted CsPbI₂Br perovskite solar cells (PeSCs). As a result, the PeSCs with improved photovoltaic performance and stability can be achieved due to the reduced defect density as well as mitigated interfacial tensile strain.

Abstract

Inorganic perovskite CsPbI₂Br has advantages of excellent thermal stability and reasonable bandgap, which make it suitable for top layer of tandem solar cells. Nevertheless, solution-processed all-inorganic perovskites generally suffer from high-density defects as well as significant tensile strain near underlayer/perovskite interface, both leading to compromised device efficiency and stability. In this work, the defect density as well as interfacial tensile strain in inverted CsPbI₂Br perovskite solar cells (PeSCs) is remarkably reduced by using a bilayer underlayer composed of dopant-free 2,2′,7,7′-tetrakis(N,N-dip-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) and copper phthalocyanine 3,4′,4″,4′″-tetrasulfonated acid tetrasodium salt (TS-CuPc) nanoparticles. As compared to control devices with pristine Spiro-OMeTAD, devices based on Spiro-OMeTAD/TS-CuPc exhibit remarkably improved photovoltaic performance and enhanced thermal/humidity stability due to the better perovskite crystallization, improved interfacial passivation, and hole-collection as well as efficient interfacial strain release. As a result, a champion efficiency of 14.85% can be achieved, which is approaching to the best reported for dopant-free and inverted all-inorganic PeSCs. The work thus provides an efficient strategy to simultaneously regulate the defects density and strain issue related to inorganic perovskites.

Publication date: September 2021

Source: Nano Energy, Volume 87

Author(s): Huyen T. Pham, Yanting Yin, Gunther Andersson, Klaus J. Weber, The Duong, Jennifer Wong-Leung

1,10-decanediol is introduced as an additive that can improve the crystalline of polymer and protect PM6 film from less erosion during the sequential deposition (SD) process. The strategy is applied to fabricate pseudo-planar heterojunction (PPHJ) organic solar cells with ideal vertical phase separation through SD processing. The champion PPHJ device demonstrates a high efficiency (16.93%) and fill factor (77.45%).

Abstract

Acquiring precision adjustable morphology of the blend films to improve the efficiency of charge separation and collection is a constant goal of organic solar cells (OSCs). Here, the above problem is improved by synergistically combining the sequential deposition (SD) method and the additive general strategy. By adding one additive 1,10-decanediol (DDO) into PM6 and another 1-chloronaphthalene (CN) into Y6, the molecule orientation of PM6 and the crystallite texture of the Y6 all become order. During the SD processing, a vertical phase separation OSCs device is formed where the donor enrichment at the anode and acceptor enrichment at the cathode. In comparison, the SD OSCs device with only CN additive still displays the bulk-heterojunction morphology similar to PM6:Y6 blend film. The morphology with vertical phase distribution can not only inhibit charge recombination but also facilitate charge collection, finally enhancing the fill factor (FF) and photocurrent in binary additives SD-type OSCs. As a result, the binary additives SD-type OSCs with blend film PM6+DDO/Y6+CN exhibit a high FF of 77.45%, enabling a power conversion efficiency as high as 16.93%. This work reveals a simple but effective approach for boosting high-efficiency OSCs with ideal morphologies and demonstrates that the additive is a promising processing alternative.

In this study, a chlorinated polymer named D18-Cl is designed and synthesized, leading to highly efficient (near 18%) organic solar cells, yet whose performance is insensitive to its molecular weight. These advantages make D18-Cl a more promising donor polymer than previously reported polymer D18 for scale-up and low-cost production.

Abstract

In the field of non-fullerene organic solar cells (OSCs), compared to the rapid development of non-fullerene acceptors, the progress of high-performance donor polymers is relatively slow. The property and performance of donor polymers in OSCs are often sensitive to the molecular weight of the polymers. In this study, a chlorinated donor polymer named D18-Cl is reported, which can achieve high performance with a wide range of polymer molecular weight. The devices based on D18-Cl show a higher open-circuit voltage (V _OC) due to the slightly deeper energy levels and an outstanding short-circuit current density (J _SC) owing to the appropriate long periods of blend films and less ([6,6]-phenyl-C71-butyric acid methyl ester) (PC₇₁BM) in mixed domains, leading to the higher efficiency of 17.97% than those of the D18-based devices (17.21%). Meanwhile, D18-Cl can achieve high efficiencies (17.30–17.97%) when its number-averaged molecular weight (M _n) is ranged from 45 to 72 kDa. In contrast, the D18-based devices only exhibit relatively high efficiencies in a narrow M _n range of ≈70 kDa. Such property and performance make D18-Cl a promising donor polymer for scale-up and low-cost production.

Multicarbazolyl-substituted benzonitrile is used as an interface manipulation layer between CsPbI₂Br and hole-transport layer, yielding the enhanced power conversion efficiency of 17.34% and stability of perovskite solar cells.

Abstract

All-inorganic CsPbI₂Br perovskite has attracted great attention as an absorber for perovskite solar cells (PSCs) due to its excellent thermal and light resistance. However, its device performance is restricted by the large energy level offset between CsPbI₂Br and the most commonly used hole-transporting layer (HTL). Herein, multicarbazolyl-substituted benzonitrile (4t-5CzBn) is inserted into the interface between CsPbI₂Br and HTL to form a uniform stepped (0.24 eV) interfacial energy level structure, which reduces the energy loss and boosts the hole extraction of CsPbI₂Br PSCs. The incorporation of 4t-5CzBn induces the increase in open-circuit voltage and fill factor from 1.256 V and 74.5% to 1.335 V and 82.3%, respectively. The optimized device achieves a power conversion efficiency of 17.34%, which is among the highest reported values of CsPbI₂Br PSCs. Besides the energy level tuning effect, the tert-butyl groups in 4t-5CzBn improve the moisture-resistance of CsPbI₂Br PSCs. The unencapsulated device maintains over 75% of its initial efficiency after 700 h storage in air. These results demonstrate that the rational tuned energy level step benefits the performance improvement of CsPbI₂Br PSCs.

Publication date: October 2021

Source: Nano Energy, Volume 88

Author(s): Ping Fu, Yang Liu, Shuwen Yu, Heng Yin, Bowen Yang, Sajjad Ahmad, Xin Guo, Can Li

An in-situ hot oxygen cleansing with superior trap passivation method is developed to prepare mixed-halide CsPbTh₃ films during ambient fabrication of solar cells. The results reveal that organic residues are removed and halide vacancies can be effectively decreased by this straightforward technique. The power conversion efficiency is increased significantly from 17.15% to 19.65% with E _loss reduction from 0.57 to 0.48 eV.

Abstract

All-inorganic perovskite CsPbI₃ has attracted extensive attention recently because of its excellent thermal and chemical stability. However, its photovoltaic performance is hindered by large energy losses (E _loss) due to the presence of point defects. In addition, hydroiodic acid (HI) is currently employed as a hydrolysis-derived precursor of intermediate compounds, which often leads to a small amount of organic residue, thus undermining its chemical stability. Herein, an in-situ hot oxygen cleansing with superior passivation (HOCP) for the triple halide-mixed CsPb(I_2.85Br_0.149Cl_0.001) perovskite solar cells (abbreviated as CsPbTh₃) deposited in an ambient atmosphere to reduce the E _loss to as low as 0.48 eV for the power conversion efficiency (PCE) to reach 19.65% is demonstrated. It is found that the hot oxygen treatment effectively removes the organic residues. Meanwhile, it passivates halide vacancies, hence reduces the trap states and nonradiative recombination losses within the perovskite layer. As a result, the PCE is increased significantly from 17.15% to 19.65% under 1 sun illumination with an open-circuit voltage enlarged to 1.23 from 1.14 V, which corresponds to an E _loss reduction from 0.57 to 0.48 eV. Also, the HOCP-treated devices exhibit better long-term stability. This insight should pave a way for decreasing nonradiative charge recombination losses for high-performance inorganic perovskite photoelectronics.

Two new small-molecule acceptors with different bandgaps are designed and synthesized for application in front and rear cells in tandem organic solar cells (OSCs) processed by non-halogenated solvents. When cooperating with appropriate polymer donors, the tandem OSCs processed by non-halogenated solvents demonstrate a power conversion efficiency of 16.67%.

Abstract

Organic solar cells (OSCs) have recently reached a remarkably high efficiency and become a promising technology for commercial application. However, OSCs with top efficiency are mostly processed by halogenated solvents and with additives that are not environmentally friendly, which hinders large-scale manufacture. In this study, high-performance tandem OSCs, based on polymer donors and two small-molecule acceptors with different bandgaps, are fabricated by solution processing with non-halogenated solvents without additive. Importantly, the two active layers developed from non-halogenated solvents show better phase segregation and charge transport properties, leading to superior performance than halogenated ones. As a result, a tandem OSC with high efficiency of up to 16.67% is obtained, showing unique advantages in future massive production.

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

Abstract

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

Regarding the bottlenecks of defect density and ion migration at grain boundary within mixed halide perovskites, the profound superiorities brought by pyridinic nitrogen-doped graphdiyne (N-GDY) are systematically highlighted. It is proposed that the spatial confinement coupling with the electrostatic repulsion effect, induced by the intrinsic 2D structure of N-GDY, contributes to the conclusive capability of impeding the halide ion migration.

Abstract

The solution processing in hybrid perovskite films inevitably results in the formation of detrimental defects at grain boundaries (GBs) that deteriorate the optoelectronic properties and bring about severe hysteresis as well as operational instability. Here, an effective scenario to alleviate the imperfection issue at perovskite GBs via incorporating pyridinic nitrogen-doped graphdiyne (N-GDY) is proposed. Taking full advantage of periodic acetylenic linkages and introduced pyridinic N atoms, the deep-level trap states like Pb–I antisite defects and under-coordinated Pb atoms are considerably passivated, thus diminishing the undesired non-radiative recombination. Additionally, the spatial confinement coupling with electrostatic repulsion effect originated from the intrinsic 2D structure of N-GDY, has been identified to deal with the halide ion migration behavior. Such contributions are further theoretically evidenced with the charge density delocalization as well as the ion migration energy barrier elevation. The authors unprecedentedly verified the superiorities based on the flexible chemical-tailorability of atomic crystal GDY materials toward polycrystalline perovskite related energy conversion devices.

Selenophene end-capped asymmetric heteroheptacene core is used to construct an efficient nonfullerene acceptor (MQ6) which shows increased carrier transport due to the enhanced O⋅⋅⋅Se intramolecular noncovalent interaction as well as the increased dipole moment. MQ6 exhibits an outstanding efficiency of 16.39 % when blended with a wide band gap copolymer.

Abstract

Nonfullerene acceptors (MQ3, MQ5, MQ6) are synthesized using asymmetric and symmetric ladder-type heteroheptacene cores with selenophene heterocycles. Although MQ3 and MQ5 are constructed with the same number of selenophene heterocycles, the heteroheptacene core of MQ5 is end-capped with selenophene rings while that of MQ3 is flanked with thiophene rings. With the enhanced noncovalent interaction of O⋅⋅⋅Se compared to that of O⋅⋅⋅S, MQ5 shows a bathochromically shifted absorption band and greatly improved carrier transport, leading to a higher power conversion efficiency (PCE) of 15.64 % compared to MQ3, which shows a PCE of 13.51 %. Based on the asymmetric heteroheptacene core, MQ6 shows an improved carrier transport induced by the reduced π–π stacking distance, related with the increased dipole moment in comparison with the nonfullerene acceptors based on symmetric cores. MQ6 exhibits a PCE of 16.39 % with a V _OC of 0.88 V, a FF of 75.66 %, and a J _SC of 24.62 mA cm⁻².

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

Abstract

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

Publication date: 16 June 2021

Source: Joule, Volume 5, Issue 6

Author(s): Furkan H. Isikgor, Francesco Furlan, Jiang Liu, Esma Ugur, Mathan K. Eswaran, Anand S. Subbiah, Emre Yengel, Michele De Bastiani, George T. Harrison, Shynggys Zhumagali, Calvyn T. Howells, Erkan Aydin, Mingcong Wang, Nicola Gasparini, Thomas G. Allen, Atteq ur Rehman, Emmanuel Van Kerschaver, Derya Baran, Iain McCulloch, Thomas D. Anthopoulos

Additive-induced synergies of defect passivation and energetic modification in perovskite solar cells are investigated, which boost power conversion efficiency and stability of the devices.

Abstract

Defect passivation via additive and energetic modification via interface engineering are two effective strategies for achieving high-performance perovskite solar cells (PSCs). Here, the synergies of pentafluorophenyl acrylate when used as additive, in which it not only passivates surface defect states but also simultaneously modifies the energetics at the perovskite/Spiro-OMeTAD interface to promote charge transport, are shown. The additive-induced synergy effect significantly suppresses both defect-assisted recombination and interface carrier recombination, resulting in a device efficiency of 22.42% and an open-circuit voltage of 1.193 V with excellent device stability. The two photovoltaic parameters are among the highest values for polycrystalline CsFormamidinium/Methylammonium (FAMA)/FAMA based n-i-p structural PSCs using low-cost silver electrodes reported to date. The findings provide a promising approach by choosing the dual functional additive to enhance efficiency and stability of PSCs.

A dopant-free small molecule hole-transporting material (HTM), SFDT-TDM, is designed and synthesized through facile routes and applied in perovskite solar cells (PVSCs). Remarkable efficiencies of 21.7% for Methylammonium (MA)-free PVSCs and 17.1% for all-inorganic PVSCs are realized, and a 1 cm² MA-free device achieves a high efficiency of 20.3%. The intrinsic hydrophobicity and dopant-free design of SFDT-TDM also enables the enhancement of device stability.

Abstract

Developing low-cost, efficient, and stable dopant-free hole-transporting materials (HTMs) in perovskite solar cells (PVSCs) is essential to their commercial deployment. Herein, the synthesis of a novel spirofluorene-dithiolane based small molecular HTM, SFDT-TDM, through facile and low-cost synthetic routes is reported. The CH^…π interactions in adjacent SFDT-TDM are beneficial for high hole mobility and the methylthio groups in SFDT-TDM can serve as Lewis bases to passivate the defects on the surface of perovskite films, leading to suppressed non-radiative recombination and enhanced charge extraction at the perovskite/HTM interface. As a result, Cs _x FA_{1− x} PbI₃ based PVSCs with SFDT-TDM as the HTM realize champion power conversion efficiencies (PCEs) of 21.7% and 20.3% for small-area (0.04 cm²) and large-area (1.0 cm²) devices with negligible photocurrent hysteresis, respectively. Additionally, all-inorganic CsPbI_{3− x} Br _x based PVSCs with SFDT-TDM demonstrate an impressive PCE of 17.1% along with excellent stability. This work highlights the great potential of the spirofluorene core for exploring low-cost and dopant-free HTMs for PVSCs with high efficiency and stability.

Perovskites with formamidinium-dominated components have revolutionized photovoltaics owing to their suitable bandgap and excellent carrier transport properties. By tunning the crystal structure stability, mitigating defect state and protecting the perovskite from complex environments, high-performance and long-term operational stable photovoltaics can be achieved. The efficient and targeted tactics for these goals are summarized and examined, providing great insight for future reaserch.

Abstract

Organic–inorganic hybrid perovskite materials have attracted widespread attention in the photovoltaic field. The best-certified perovskite single-junction photovoltaics have achieved an impressive power conversion efficiency of 25.5%. Particularly, formamidinium lead triiodide (FAPbI₃) perovskite material has been considered to be one of the most promising materials for fabricating highly efficient single-junction solar cells due to its suitable bandgap (1.43 eV). However, the metastable α-FAPbI₃ perovskite phase, which can spontaneously transform into the undesirable δ phase, limits their further applications. Accordingly, stabilizing the α phase and achieving high-quality films are keys for achieving high-efficiency and long-term operational perovskite photovoltaics. In this review, strategies for stabilization of α-FAPbI₃ are discussed in detail, and the corresponding thermodynamic mechanisms are also summarized. Moreover, the methods to eliminate defects and improve carrier transport are thoroughly reviewed, which is important for achieving high-performance photovoltaic devices with outstanding long-term operational stability. Finally, possible the future research directions of FAPbI₃ photovoltaics toward commercialization are discussed.

Novel hole transport material CPDA 1 can be efficiently and inexpensively synthesized from readily available starting materials. The cyclopentadiene acetal core is surrounded by four triarylamine arms in a star-shaped fashion. Excellent optoelectronic, thermal, and transport properties lead to high power conversion efficiencies of 23.1% in perovskite solar cells with respectable long-term stability.

Abstract

Hole transport materials (HTM) are an important component in perovskite solar cells (PSC). Despite a multitude of HTMs developed in recent years, only few of them lead to solar cells with efficiencies over 20%. Therefore, it is still a challenge to develop high-performing HTMs, which have ideal energy levels of the frontier orbitals, are highly efficient in transporting charges, and stabilize the solar cell at the same time. In this work, the development of a structurally novel molecular HTM, CPDA 1, is described which is based on a common cyclopentadiene core and can be efficiently and inexpensively synthesized from readily available starting materials, which is important for future realization of low-cost photovoltaics on larger scale. Due to excellent optoelectronic, thermal, and transport properties, CPDA 1 not only meets the envisioned properties by reaching high efficiencies of 23.1%, which is among the highest reported to date, but also contributes to a respectable long-term stability of the PSCs.

Using an innovative quantum mechanical method for an open quantum system, we observe in real time and space the generation, migration, and dissociation of electron-hole pairs, transport of electrons and holes, and current emergence in an organic photovoltaic cell. Ehrenfest dynamics is used to study photoexcitation of thiophene:fullerene stacks coupled with a time-dependent density functional tight-binding method. Our results display the generation of an electron-hole pair in the donor and its subsequent migration to the donor-acceptor interface. At the interface, electrons transfer from the lowest unoccupied molecular orbitals (LUMOs) of thiophenes to the second LUMOs of fullerene. Further migration of electrons and holes leads to the emergence of current. These findings support previous experimental evidence of coherent couplings between electronic and vibrational degrees of freedom and are expected to stimulate further work toward exploring the interplay between electron-hole pair (exciton) binding and vibronic coupling for charge separation and transport.

Nature Energy, Published online: 14 June 2021; doi:10.1038/s41560-021-00830-9

By using a removable polymer film, transfer of perovskite arrays to planar or nonplanar surfaces is realized. The total thickness of the fabricated perovskite device is thin enough to form conformal contact on various surfaces with 3D geometries. This work provides the integration of perovskites on contact lenses and pressure sensors, achieving multiplexed sensing platforms for future electronics.

Abstract

Despite recent substantial advances in perovskite materials, their 3D integration capability for next-generation electronic devices is limited owing to their inherent vulnerability to heat and moisture with degradation of their remarkable optoelectronic properties during fabrication processing. Herein, a facile method to transfer the patterns of perovskites to planar or nonplanar surfaces using a removable polymer is reported. After fabricating perovskite devices on this removable polymer film, the conformal attachment of this film on target surfaces can place the entire devices on various substrates by removing this sacrificial film. This transfer method enables the formation of a perovskite image sensor array on a soft contact lens, and in vivo tests using rabbits demonstrate its wearability. Furthermore, 3D heterogeneous integration of a perovskite photodetector array with an active-matrix array of pressure-sensitive silicon transistors using this transfer method demonstrates the formation of a multiplexed sensing platform detecting distributions of light and tactile pressure simultaneously.

Recent progress on perovskite surface and interface science of perovskite optoelectronic devices is summarized. The impact of various surface and interface defects on heterojunction energy barriers and carrier dynamics in devices is reviewed and discussed. Practical engineering methods to mitigate these defects at various interfaces in devices are also considered.

Abstract

Surfaces and heterojunction interfaces, where defects and energy levels dictate charge-carrier dynamics in optoelectronic devices, are critical for unlocking the full potential of perovskite semiconductors. In this progress report, chemical structures of perovskite surfaces are discussed and basic physical rules for the band alignment are summarized at various perovskite interfaces. Common perovskite surfaces are typically decorated by various compositional and structural defects such as residual surface reactants, discrete nanoclusters, reactions by products, vacancies, interstitials, antisites, etc. Some of these surface species induce deep-level defect states in the forbidden band forming very harmful charge-carrier traps and affect negatively the interface band alignments for achieving optimal device performance. Herein, an overview of research progresses on surface and interface engineering is provided to minimize deep-level defect states. The reviewed subjects include selection of interface and substrate buffer layers for growing better crystals, materials and processing methods for surface passivation, the surface catalyst for microstructure transformations, organic semiconductors for charge extraction or injection, heterojunctions with wide bandgap perovskites or nanocrystals for mitigating defects, and electrode interlayer for preventing interdiffusion and reactions. These surface and interface engineering strategies are shown to be critical in boosting device performance for both solar cells and light-emitting diodes.

Newly synthesized hexabenzocoronene (HBC)–osmapentalyne complexes that combine fragments of graphene and metalla-aromatics are emerging as cathode interlayer materials. Further extending the d_π –p_π conjugated systems of osmapentalynes, the most successful complex, in this work, HBC-S is found to boost the efficiency of non-fullerene solar cells to over 18%.

Abstract

Interface engineering is a critical method by which to efficiently enhance the photovoltaic performance of nonfullerene solar cells (NFSC). Herein, a series of metal–nanographene-containing large transition metal involving d_π –p_π conjugated systems by way of the addition reactions of osmapentalynes and p-diethynyl-hexabenzocoronenes is reported. Conjugated extensions are engineered to optimize the π-conjugation of these metal–nanographene molecules, which serve as alcohol-soluble cathode interlayer (CIL) materials. Upon extension of the π-conjugation, the power conversion efficiency (PCE) of PM6:BTP-eC9-based NFSCs increases from 16% to over 18%, giving the highest recorded PCE. It is deduced by X-ray crystallographic analysis, interfacial contact methods, morphology characterization, and carrier dynamics that modification of hexabenzocoronenes-styryl can effectively improve the short-circuit current density (J _sc) and fill factor of organic solar cells (OSCs), mainly due to the strong and ordered charge transfer, more matching energy level alignments, better interfacial contacts between the active layer and the electrodes, and regulated morphology. Consequently, the carrier transport is largely facilitated, and the carrier recombination is simultaneously impeded. These new CIL materials are broadly able to enhance the photovoltaic properties of OSCs in other systems, which provides a promising potential to serve as CILs for higher-quality OSCs.

In this work, thermally deposited γ-CsPbI₃ perovskite solar cells that include small amounts of coevaporated phenylethylammonium iodine (PEAI) are demonstrated. The incorporation of PEAI leads to highly oriented γ-CsPbI₃ films with improved microstructure and reduced density of defects. The resulting solar cells reach an efficiency of 15% and exhibit an excellent shelf-storage, thermal and photostability.

Abstract

Thin-film deposition by thermal evaporation offers many advantages, yet in the field of perovskite photovoltaics solution-processed devices significantly outperform those fabricated by thermal evaporation. Here, high-quality γ-CsPbI₃ perovskite layers by coevaporation of PbI₂ and CsI with a small amount of phenylethylammonium iodide (PEAI) are deposited. It is demonstrated that the addition of PEAI into the perovskite layers leads to a preferred crystal orientation and a far improved microstructure, with columnar domains that protrude throughout the film's thickness. This is accompanied by a reduced density of defects as evidenced by the increase in photoluminescence and decrease in Urbach energy as compared to reference CsPbI₃ films. Photovoltaic devices based on the PEAI containing perovskite layers reach up to 15% in power conversion efficiency, thus surpassing not only the performance of reference CsPbI₃ devices, but also that of most solution-processed PEAI containing inorganic CsPbX₃ (X = Cl, Br, I) perovskite solar cells. Importantly, encapsulated thermally evaporated perovskite devices maintain their performance for over 215 days, demonstrating the stabilizing effect of PEAI on thermally evaporated CsPbI₃.