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The highly adaptable optoelectronic and morphological properties of non-fullerene acceptors (NFAs) have made them a prominent research topic in the organic solar cell (OSC) field. This work describes the design of new molecules and investigates the potential optoelectronic aspects of remodified Y-series NFAs endowing with five new semi-circular shaped derivatives (BTPB1-BTPB5) based on the DFT-based quantum simulations. The designed molecules possess higher-lying LUMO energy levels with narrowed bandgaps and excellent coherence between the acceptor and core via inserted bridges. The molecules demonstrate a significant red shift and a wide-ranging absorption spectrum extending from 400 nm to 1500 nm, with the most extensive absorption occurring in the near-infrared (NIR) region. Effective π-π stacking and drastically lower binding energy certify facile charge dissociation and transmission rate. Thiophene-based bridge modification decreased reorganization energy by 47 % which results in facile charge transmission and high current density. Theoretically, simulated PCE is achieved as high as 31.49 % owing to the higher-lying LUMOs. The results demonstrate the value of designing systems and exploring new possibilities for developing effective Y-series NFAs-based high-performance organic solar cells.
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Two quinoxaline dyes utilized in copper-electrolyte-based dye-sensitized solar cells (Cu-DSSCs) are theoretically investigated to analyze the impact of alkyl chains on dye performance. The investigation shows that ZS4, known for its record efficiency of up to 13.2 %, exhibits higher electron coupling and fewer binding sites for dye-[Cu(tmby)2]2+ interaction compared to ZS5. Contrary to common belief, alkyl chains are found to not only provide shielding but also hinder the interaction between dye and [Cu(tmby)2]2+ by influencing the optimal conformation of dyes, thereby impeding the charge recombination process. It is crucial to consider the influence of alkyl chains on dye conformation when discussing the relationship between dye structure and performance, rather than oversimplifying it as often done traditionally. Building on these findings, eight dyes are strategically designed by adjusting the position of the alkyl chain to further decrease charge recombination compared to ZS4. Theoretical evaluation of these dyes reveals that changing the alkyl chain on the nitrogen atom from 2-ethylhexyl (ZS4) to 1-hexylheptyl (D3-2) not only reduces the charge recombination rate but also enhances light harvesting ability. Therefore, D3-2 shows potential as a candidate for experimental synthesis of high-performance Cu-DSSCs with improved efficiency.
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Silicon heterojunction (SHJ) solar cells have set world-record efficiencies among single-junction silicon solar cells, accelerating their commercial deployment. Despite these clear efficiency advantages, the high costs associated with low-temperature silver pastes (LTSP) for metallization have driven the search for more economical alternatives in mass production. 2D transition metal carbides (MXenes) have attracted significant attention due to their tunable optoelectronic properties and metal-like conductivity, the highest among all solution-processed 2D materials. MXenes have emerged as a cost-effective alternative for rear-side electrodes in SHJ solar cells. However, the use of MXene electrodes has so far been limited to lab-scale SHJ solar cells. The efficiency of these devices has been constrained by a fill factor (FF) of under 73%, primarily due to suboptimal charge transport at the contact layer/MXene interface. Herein, a silver nanowire (AgNW)-assisted Ti3C2Tx MXene electrode contact is introduced and explores the potential of this hybrid electrode in industry-scale solar cells. By incorporating this hybrid electrode into SHJ solar cells, 9.0 cm2 cells are achieved with an efficiency of 24.04% (FF of 81.64%) and 252 cm2 cells with an efficiency of 22.17% (FF of 76.86%), among the top-performing SHJ devices with non-metallic electrodes to date. Additionally, the stability and cost-effectiveness of these solar cells are discussed.
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Dimeric acceptors are expected to satisfy both excellent power conversion efficiency (PCE) and operational stability of organic solar cells (OSCs). However, comparing to highly planar and symmetrical monomer-like acceptors, the quite different steric/spatial configurations of dimeric acceptors affect device outcomes greatly. Herein, on basis of the same dimeric molecular platform that constructed by bridging central units of two monomer-like acceptor, diverse substituents (âOCH3 for D1, âCH3 for D2, and âCF3 for D3) are grafted on central units to regulate the three dimensions (3D) geometries of dimeric acceptors delicately. A systematic investigation reveals the substituent-dependent variation of energy level, absorption, and molecular packing behavior. Consequently, D2 acceptor, characteristic of more favorable configuration, affords a superior film morphology and charge transfer/transport dynamics in resulting OSCs, thus yielding an excellent PCE of 17.50% along with a good long-term stability. This work manifests the crucially important role of central substituents in constructing high-performance dimeric acceptors.
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The dimerization of small molecule acceptors (SMAs) holds significant potential by combining the advantages of both SMAs and polymer acceptors in realizing high power conversion efficiency (PCE) and operational stability in organic solar cells (OSCs). However, advancements in the selection and innovation of dimeric linkers are still challenging in enhancing their performance. In this study, three new dimeric acceptors, namely DY-Ar-4, DY-Ar-5, and DY-Ar-6 are synthesized, by linking two Y-series SMA subunits via an "end-to-end" strategy using flexible spacers (octyl, decyl, and dodecyl, respectively). The influence of spacer lengths on device performance is systematically investigated. The results indicate that DY-Ar-5 exhibits more compact and ordered packing, leading to an optimal morphology. OSCs based on PM6: DY-Ar-5 achieves a maximum PCE of 15.76%, attributes to enhance and balance carrier mobility, and reduce carrier recombination. This dimerization strategy using suitable non-conjugated linking units provides a rational principle for designing high-performance non-fullerene acceptors.
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The photocatalytic activity and inherent brittleness of ZnO, which is commonly used as an electron transport layer (ETL) in inverted organic solar cells (OSCs), have impeded advancements in device stability and the development of fully stretchable OSCs. In this study, we have developed an intrinsically stretchable ETL for inverted OSCs through a side-chain cross-linking strategy. Specifically, cross-linking between bromine atoms on the side chains of a quinoidal compound and the amino groups in polyethylenimine resulted in a film, designated QBr-PEI-50, with high electrical conductivity (0.049 S/m) and excellent stretchability (crack-onset strain >45%). When used as the ETL in inverted OSCs, QBr-PEI-50 was markedly superior to ZnO in terms of device performance and stability, yielding a power conversion efficiency (PCE) of 18.27% and a T80 lifetime exceeding 10000 h. Moreover, incorporation of QBr-PEI-50 in fully stretchable inverted OSCs yielded a PCE of 14.01%, and 80% of the initial PCE was maintained after 21% strain, showcasing its potential for wearable electronics.
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Single dyes typically exhibit limited light absorption in dye-sensitized solar cells (DSSCs). Thus, cosensitization using two or more dyes to enhance light-harvesting efficiency has been explored; however, the aggregation of dyes can adversely affect electron injection capabilities. This study focused on the design and synthesis of three dyes with a common carbazole donor for DSSCs: DZ102, TZ101, and JM102. JM102 broadens the absorption spectrum by replacing the benzoic acid electron acceptor of TZ101 with acetylenic benzoic acid. A cosensitized DSSC device based on CO-1 [DZ102:TZ101 = 1:1 (50 µM:50 µM)] achieved a short-circuit current density of 19.4 mA/cm2 and a power conversion efficiency of 10.9%. For the first time, the molecular interactions between the dyes in the photoanode were demonstrated using cyclic voltammetry, which revealed the presence of intermolecular forces. Adsorption kinetics further indicated that these forces promoted the self-assembly of dyes during adsorption, which resulted in a cosensitization adsorption amount greater than the sum of the individual dye adsorptions. This study provides novel insights into the selection of cosensitizing dyes for DSSCs.
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Electron-withdrawing molecules (EWMs) have exhibited remarkable efficacy in boosting the performance of perovskite solar cells (PSCs). However, the underneath mechanisms governing their positive attributes remain inadequately understood. Herein, we conducted a comprehensive study on EWMs by comparing 2,2'-(2,5-cyclohexadiene-1,4-diylidene) bismalononitrile (TCNQ) and (2,3,5,6-tetrafluoro-2,5-cyclohexadiene-1,4-diylidene) dimalononitrile (F4TCNQ) employed at the perovskite/hole transport layer (HTL) interfaces. Our findings reveal that EWMs simultaneously enhance chemical passivation, interface dipole effect, and chemically binding of the perovskite to the HTL. Notably, F4TCNQ, with its superior electron-withdrawing properties, demonstrates a more pronounced impact. Consequently, PCSs modified with F4TCNQ achieved an impressive power conversion efficiency (PCE) of 25.21%, while demonstrating excellent long-term stability. Moreover, the PCE of a larger-area perovskite module (14.0 cm2) based on F4TCNQ reached 21.41%. This work illuminates the multifaceted mechanisms of EWMs at the interfaces in PSCs, delivering pivotal insights that pave the way for the sophisticated design and strategic application of EWMs, thereby propelling the advancement of perovskite photovoltaic technology.
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Simultaneously controlling defects and film morphology at the buried interface is a promising approach to improve the power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs). Here, two new donorâacceptor type semiconductive covalent organic frameworks (COFs) are developed, COFTPA and COFICZ. The carefully designed COFs structure not only effectively regulates the morphology and defects of the buried interface film, but also realizes the alignment with the energy level of the perovskite film and enhances the extraction and transmission of the interface charge. Among them, COFICZ-treated inverted PSCs achieved a maxmum PCE of 25.68% (certified 25.14%), the inverted PCE reached a minimum PCE of 22.92% for 1 cm2 device. The efficiency of inverted PSCs with a 1.68 eV wide bandgap reached 22.92%, which is the highest datum of the reported 1.68 eV wide bandgap PSC. This lays the groundwork for the commercialization of perovskite/silicon tandem solar cells. Additionally, the unencapsulated devices demonstrated a high degree of stability during operational use and when subjected to conditions of high humidity and temperature.
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The electron transporting layer (ETL) used in high performance inverted perovskite solar cells (PSCs) is typically composed of C60, which requires time-consuming and costly thermal evaporation deposition, posing a significant challenge for large-scale production. To address this challenge, herein, we present a novel design of solution-processible electron transporting material (ETM) by grafting a non-fullerene acceptor fragment onto C60. The synthesized BTPC60 exhibits an exceptional solution processability and well-organized molecular stacking pattern, enabling the formation of uniform and structurally ordered film with high electron mobility. When applied as ETL in inverted PSCs, BTPC60 not only exhibits excellent interfacial contact with the perovskite layer, resulting in enhanced electron extraction and transfer efficiency, but also effectively passivates the interfacial defects to suppress non-radiative recombination. Resultant BTPC60-based inverted PSCs deliver an impressive power conversion efficiency (PCE) of 25.3% and retain almost 90% of the initial values after aging at 85°C for 1500 hours in N2. More encouragingly, the solution-processed BTPC60 ETL demonstrates remarkable film thickness tolerance, and enables a high PCE up to 24.8% with the ETL thickness of 200 nm. Our results highlight BTPC60 as a promising solution-processed fullerene-based ETM, opening an avenue for improving the scalability of efficient and stable inverted PSCs.
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The latest development in perovskite solar cell (PSC) technology has been significantly influenced by advanced techniques aimed at passivating surface defects. This work presents a new approach called thermal imprinting-assisted ion exchange passivation (TIAIEP), which delivers a different approach to conventional solution-based methods. TIAIEP focuses on addressing surface imperfections in solid-state films by using a passivator that promotes ion exchange specifically at the defect sites within the perovskite layer. By adjusting the time and temperature of the TIAIEP process, we achieve substantial enhancement in the creation of a compositional gradient within the films. This optimization slows the cooling rate of hot carriers, leading to minimizing charge recombination and improving the device performance. Remarkably, devices treated with TIAIEP achieve a 22.29% power conversion efficiency and show outstanding stability, with unencapsulated PSCs maintaining 91% of their original efficiency after over 2000 h of storage and 90% efficiency after 1200 h of constant illumination. These results highlight TIAIEP's effectiveness in mitigating surface defects, improving both the photoelectric and stability performance of PSCs, and indicating significant potential for large-scale application in perovskite film passivation, promoting the widespread adoption of this technology.
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Significant challenges in ensuring long-term stability, addressing environmental safety issues, and improving efficiency have hindered the commercialization of inverted Pb-based halide perovskite solar cells (PeSCs). One reasonable approach to addressing these issues is to place an effective buffer layer between the perovskite active layer and the electrode. In this study, we demonstrate the use of crown ether, di-tert-butyl dibenzo-18-crown-6, as a single buffer layer to improve the efficiency, long-term stability, and environmental safety of PeSCs for the first time. The crown ether buffer layer suppressed Ag diffusion from the Ag metal electrodes, thereby improving the performance and lifetime of the device. In addition, it effectively captures Pb ions that may leak into the environment during the whole lifetime of devices, thereby enhancing the environmental safety of PeSCs. Furthermore, PeSCs incorporating crown ethers as buffer layers demonstrated enhanced stability in a nitrogen atmosphere and achieved a high power conversion efficiency of 22.8%. Consequently, this crown ether buffer layer offers an effective and straightforward strategy capable of achieving efficient, stable, and environmentally safe PeSCs.
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Oligomerized small molecular acceptors (OSMAs) have rapidly become a research hotspot in the field of organic solar cells due to their advantages of effective combination with definite structure of small molecules and high viscosity and glass transition temperature of polymers. From this perspective, we classify and summarize the representative OSMAs from the three binding sites of end, core, and wing, and we summarize the exploration of new synthesis methods to improve the plights, such as low synthesis yield and difficult purification. Finally, the existing challenges and future research directions are concluded and prospected.
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The exploration of novel two-dimensional (2D) materials with a direct band gap and high mobility has attracted huge attention due to their potential application in electronic and optoelectronic devices. Here, we propose a feasible way to construct multiatomic monolayer Ca2A2Z5 (A = Al and Ga and Z = S, Se, and Te) by first-principles calculations. Our results indicated that the energies of α1-phase Ca2A2Z5 are slightly lower than those of experimentally synthesized α3-phase-like Ca2A2Z5 monolayers with excellent structural stability. Moreover, the α1- and α3-phase Ca2A2Z5 monolayers possess not only direct band gaps but also high electron mobilities (up to â¼103 cm2 V-1 s-1), demonstrating an intriguing range of visible light absorption. Importantly, α1- and α3-phase Ca2Ga2Se5 monolayers are good donor materials, and the corresponding Ca2Ga2Se5/ZrSe2 type-II heterostructures exhibit desirable power conversion efficiencies of 22.4% and 22.9%, respectively. Our findings provide a feasible way to explore new 2D materials and offer several Ca2A2Z5 candidate monolayers for the application of high-performance solar cells.
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Poly (3-hexylthiophene) (P3HT) is one of the most efficient hole transport layers (HTLs) in perovskite solar cells (PSCs). However, surface and boundary defects in CsPbI3, and energy level mismatch between CsPbI3 and P3HT lead to a low power conversion efficiency (PCE) in P3HT-based CsPbI3 PSCs. Here, a synergistic strategy with anti-solvent (sec-pentyl alcohol, 2-PA) and passivators (LiX, X = F, Cl, Br, I) is developed to promote the photovoltaic performance of P3HT-based CsPbI3 PSCs. It is proved that the 2-PA washes away the residual DMF and DMAPbI3, and assists the secondary growth of CsPbI3 crystal. LiX not only can passivate iodine (I) vacancies, but also can reduce energy offset at CsPbI3/P3HT interface, accelerating hole extraction process. Finally, an impressive efficiency of 19.26% is obtained due to the synergistic effect of defects passivation and energy alignment, which is 34.4% higher than the 14.32% achieved in Control cell. These findings prove that synergistic strategy of defects passivation and energy alignment is an effective way for realizing high-efficiency in P3HT-based CsPbI3 PSCs.
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The difluorobenzothiadizole (ffBT) unit is one of the most classic electron-accepting building blocks used to construct D-A copolymers for applications in organic solar cells (OSCs). Historically, ffBT-based polymers have achieved record power conversion efficiencies (PCEs) in fullerene-based OSCs owing to their strong temperature-dependent aggregation (TDA) characteristics. However, their excessive miscibility and rapid aggregation kinetics during film formation have hindered their performance with state-of-the-art non-fullerene acceptors (NFAs). Herein, we synthesized two ffBT-based copolymers, PffBT-2T and PffBT-4T, incorporating different π-bridges to modulate intermolecular interactions and aggregation tendencies. Experimental and theoretical studies revealed that PffBT-4T exhibits reduced electrostatic potential differences and miscibility with L8-BO compared to PffBT-2T. This facilitates improved phase separation in the active layer, leading to enhanced molecular packing and optimized morphology. Moreover, PffBT-4T demonstrated a prolonged nucleation and crystal growth process, leading to enhanced molecular packing and optimized morphology. Consequently, PffBT-4T-based devices achieved a remarkable PCE of 17.5%, setting a new record for ffBT-based photovoltaic polymers. Our findings underscore the importance of conjugate backbone modulation in controlling aggregation behavior and film formation kinetics, providing valuable insights for the design of high-performance polymer donors in organic photovoltaics.
RESUMEN
Three small donor molecule materials (S1, S2, S3) based on dithiophene [2,3-d:2',3'-d']dithiophene [1,2-b:4,5-b']dithiophene (DTBDT) utilized in this study were synthesized using the Vilsmeier-Haack reaction, traditional Stille coupling, and Knoevenagel condensation. Then, a variety of characterization methods were applied to study the differences in optical properties and photovoltaic devices among the three. By synthesizing S2 using a thiophene π-bridge based on S1, the blue shift in ultraviolet absorption can be enhanced, the band gap and energy level can be reduced, the open circuit voltage (VOC) can be increased to 0.75 V using the S2:Y6 device, and a power conversion efficiency (PCE) of 3% can be achieved. Also, after developing the device using Y6, S3 introduced the alkyl chain of thiophene π-bridge to S2, which improved the solubility of tiny donor molecules, achieved the maximum short-circuit current (JSC = 10.59 mA/cm2), filling factor (FF = 49.72%), and PCE (4.25%). Thus, a viable option for future design and synthesis of small donor molecule materials is to incorporate thiophene π-bridges into these materials, along with alkyl chains, in order to enhance the device's morphology and charge transfer behavior.
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Interfacial engineering is of great concern in photovoltaic devices. Metal halide perovskite solar cells (PSCs) have garnered much attention due to their impressive development in power conversion efficiencies (PCEs). Benefiting from high electron mobility and good energy-level alignment with perovskite, aqueous SnO2 as an electron transport layer has been widely used in n-i-p perovskite solar cells. However, the interfacial engineering of an aqueous SnO2 layer on PSCs is still an obscure and confusing process. Herein, we proposed the preparation of n-i-p perovskite solar cells with different concentrations of SnO2 as electron transport layers and achieved optimized PCE with an efficiency of 20.27%. I Interfacial engineering with regard to the SnO2 layer is investigated by observing the surface morphology, space charge-limited current (SCLC) with the use of an electron-only device, and time-resolved photoluminescence (TRPL) of perovskite films.
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In recent years, the power conversion efficiency of perovskite solar cells has increased rapidly. Perovskites can be prepared using simple and cost-effective solution methods. However, the perovskite films obtained are usually polycrystalline and contain numerous defects. Passivation of these defects is crucial for enhancing the performance of solar cells. Here, we report the use of propylamine hydroiodide (PAI) for defect passivation. We found that PAI can result in higher-efficiency cells by reducing the defects and suppressing non-radiative recombination. Consequently, n-i-p perovskite solar cells with a certificated efficiency of 21% were obtained. In addition, PAI exhibited excellent performance in p-i-n devices by serving as a buried interface layer, leading to an improved efficiency of 23%.
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Precursor solution aging process can cause significant influence on the photovoltaic performance of perovskite solar cells (PVSCs). Notably, we first observe that the aging phenomenon is more severe in the precursor of two-step sequential method compared to that in one-step method due to that the protic solvent isopropanol facilitates amine-cation side reaction and iodide ions oxidation. Herein, we report a novel approach for selectively stabilizing both organic amine salt and lead iodide (PbI2) precursor solutions in two-step method. The introduction of benzene-1,3-dithiol into organic amine salt solution can mitigate amine-cation side reactions due to the formation of an acidic and reducing environment. Simultaneously, decamethylferrocene (FcMe10/FcMe+10) pair can act as a redox shuttle in PbI2 solution to concurrently oxidize Pb0 and reduce I2 in cyclic manner. Consequently, the PVSCs device fabricated from ameliorative precursor solutions demonstrates superior power conversion efficiency of 25.31%, retaining 95% of its efficiency after 21 days of solution aging. Moreover, the unencapsulated devices maintain 85% of primitive efficiency for 1500 h at maximum power point tracking under continuous illumination. This work establishes a fundamental guidance and scientific direction for the stabilization of two-step perovskite precursor solutions.