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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.

A cation deficiency-induced phase separation strategy is proposed to design perovskite-based composites with the ability to achieve accurate control over the composition, structure, and content of the component phases, which strongly interact with one another, leading to significantly promoted water oxidation kinetics due likely to enhanced lattice-oxygen participation at the dual-phase interface.

Abstract

Single-phase perovskite oxides that contain nonprecious metals have long been pursued as candidates for catalyzing the oxygen evolution reaction, but their catalytic activity cannot meet the requirements for practical electrochemical energy conversion technologies. Here a cation deficiency-promoted phase separation strategy to design perovskite-based composites with significantly enhanced water oxidation kinetics compared to single-phase counterparts is reported. These composites, self-assembled from perovskite precursors, comprise strongly interacting perovskite and related phases, whose structure, composition, and concentration can be accurately controlled by tailoring the stoichiometry of the precursors. The composite catalyst with optimized phase composition and concentration outperforms known perovskite oxide systems and state-of-the-art catalysts by 1–3 orders of magnitude. It is further demonstrated that the strong interfacial interaction of the composite catalysts plays a key role in promoting oxygen ionic transport to boost the lattice-oxygen participated water oxidation. These results suggest a simple and viable approach to developing high-performance, perovskite-based composite catalysts for electrochemical energy conversion.

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.

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.

A synergistic passivation mechanism of a mixed-salt treatment through surface reconstruction engineering is unraveled. This strategy reduces defects and suppresses ion migration of the perovskite interface, leading to enhanced photovoltaic performance meanwhile presenting outstanding operational stability. More generally, the proposed mixed-salt system provides a wider way of designing functional passivation materials, which gets benefits from its synergistic effect.

Abstract

Surface passivation treatment is a widely used strategy to resolve trap-mediated nonradiative recombination toward high-efficiency metal-halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in-depth understanding of its passivation mechanism. Here, a systematic study on a mixed-salt passivation strategy of formamidinium bromide (FABr) coupled with different F-substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F-substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed-salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI₂. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high-quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed-salt treatment. In addition, the introduction of the moisture resisted F-substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long-term stability under a high humid atmosphere as well as operational conditions.

Lycopene, a botanic antioxidant, is introduced to modify the perovskite film for adjusting crystallization through carbon-halogen bonds, and preventing moisture and oxygen erosion. Therefore, the optimized device yields efficiencies of 21.04% under 100 mW cm⁻² and 40.24% at 1000 lux. It also retains almost 90% of the original efficiency value after exposure to wet oxygen ambience for 1000 h.

Abstract

Perovskite (PVSK) photovoltaics have been a promising field in the exploitation of renewable energy due to the fascinating performances of PVSK materials and devices. Although the efficiency is gradually approaching that of traditional solar cells, the stability is still a challenge. Hence, tomato lycopene, a botanic antioxidant, is introduced as a modification layer on the PVSK absorber layer to prevent moisture and oxygen erosion, for enhanced both intrinsic and environmental stabilities. This inserted protection layer can also interact with the PVSK material through carbon-halogen bonds and influence its crystallinity. Therefore, PVSK films are obtained with less defects and better intrinsic stability. The device achieved a champion outdoor efficiency at AM 1.5G more than 21% and its indoor efficiency at 1000 lux can reach 40.24%. In addition, the efficiency can keep almost 90% of the original value after exposure to wet oxygen ambience for 1000 h. The antioxidant gives a unique perspective towards enhancing the stability of solar cells

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.

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.

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

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

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

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.

A self-assemble passivation of PbS colloidal quantum dots (CQDs) is reported to improve the photovoltaic performance of infrared CQD solar cells. Extensive experimental studies and theoretical calculations are performed, which reveal that the high performance is attributed to the strong coupling and improved defect passivation of CQDs, resulting in diminished trap-assisted charge recombination in the CQD solid films.

Abstract

The surface passivation of colloidal quantum dots (CQD) is critical for the electronic coupling of CQDs, which significantly affects the photovoltaic performance of CQD solar cells (CQDSCs). Herein, a self-assemble passivation (SAP) strategy of CQDs is introduced to improve CQD coupling. The PbI₂ passivation layer prepared using the SAP method can largely improve surface defect passivation of CQDs, diminishing charge recombination induced by the sub-bandgap traps. Meanwhile, extensive theoretical simulations reveal that the self-assembled PbI₂ passivation layer works as a “charger bridge” for charge transport between the adjacent CQDs, avoiding CQD fusion. The infrared CQDSCs are fabricated and the SAP-based CQDSC yields an efficiency of up to 12.3%, which is significantly improved compared with that of the conventional CQDSCs with iodide passivating CQD surface. The improved photovoltaic performance in the SAP-based CQDSCs is attributed to increased charge extraction, resulting from strong CQD coupling within the CQD solid films. This work provides a simple and facile way to improve the electronic coupling of CQDs for high-performance infrared CQDSCs.

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

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.

The same coordination chemistry of Ag⁺ and Cu⁺ in dimethyl sulfoxide solution results in the successful fabrication of solid solution (Ag _x ,Cu_{1− x} )₂ZnSnS₄ (x = 0≈1). The novel Ag incorporation strategy significantly reduces band tailing, and a champion kesterite solar cell with an efficiency of 12.5% and a record low open circuit voltage (V _oc) loss (V _oc/V _oc ^SQ of 64.2%) is achieved with 5% Ag incorporation.

Abstract

The large open-circuit voltage deficit (V _oc,def) is the key issue that limits kesterite (Cu₂ZnSn(S,Se)₄, [CZTSSe]) solar cell performance. Substitution of Cu⁺ by larger ionic Ag⁺ ((Ag,Cu)₂ZnSn(S,Se)₄, [ACZTSSe]) is one strategy to reduce Cu–Zn disorder and improve kesterite V _oc. However, the so far reported ACZTSSe solar cell has not demonstrated lower V _oc,def than the world record device, indicating that some intrinsic defect properties cannot be mitigated using current approaches. Here, incorporation of Ag into kesterite through a dimethyl sulfoxide (DMSO) solution that can facilitate direct phase transformation grain growth and produce a uniform and less defective kesterite absorber is reported. The same coordination chemistry of Ag⁺ and Cu⁺ in the DMSO solution results in the same reaction path of ACZTSSe to CZTSSe, resulting in significant suppression of Cu_Zn defects, its defect cluster [2Cu_Zn + Sn_Zn], and deep level defect Cu_Sn. A champion device with an efficiency of 12.5% (active area efficiency 13.5% without antireflection coating) and a record low V _oc,def (64.2% Shockley–Queisser limit) is achieved from ACZTSSe with 5% Ag content.

This work presents a facile, low-cost, and upscalable process for depositing a mesoporous NiO _x (mp-NiO _x ) layer based on a polymer templating approach by spin-coating. Herein, this templated mp-NiO _x film is employed as a hole-transport layer in inverted perovskite solar cells with an outstanding efficiency larger than 20%. The beneficial effects of this mp-NiO _x layer, such as negligible hysteresis and reduced recombination losses are demonstrated.

Abstract

Despite the outstanding role of mesoscopic structures on the efficiency and stability of perovskite solar cells (PSCs) in the regular (n–i–p) architecture, mesoscopic PSCs in inverted (p–i–n) architecture have rarely been reported. Herein, an efficient and stable mesoscopic NiO _x (mp-NiO _x ) scaffold formed via a simple and low-cost triblock copolymer template-assisted strategy is employed, and this mp-NiO _x film is utilized as a hole transport layer (HTL) in PSCs, for the first time. Promisingly, this approach allows the fabrication of homogenous, crack-free, and robust 150 nm thick mp-NiO _x HTLs through a facile chemical approach. Such a high-quality templated mp-NiO _x structure promotes the growth of the perovskite film yielding better surface coverage and enlarged grains. These desired structural and morphological features effectively translate into improved charge extraction, accelerated charge transportation, and suppressed trap-assisted recombination. Ultimately, a considerable efficiency of 20.2% is achieved with negligible hysteresis which is among the highest efficiencies for mp-NiO _x based inverted PSCs so far. Moreover, mesoscopic devices indicate higher long-term stability under ambient conditions compared to planar devices. Overall, these results may set new benchmarks in terms of performance for mesoscopic inverted PSCs employing templated mp-NiO _x films as highly efficient, stable, and easy fabricated HTLs.

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.