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Interface engineering by using TiO2 nanocubic modifier in planar heterojunction perovskite solar cells
摘要： In this work we adopt a nanoscale TiO2 nanocubic particle as interfacial modifier between compact TiO2 layer and CH3NH3PbI3 layer. The TiO2 nanocubic modifier can passivate the defect states and suppress charge recombination at the TiO2/MAPbI3 interface. As a result, the photovoltaic performances of planar heterojunction perovskite solar cells were effectively boosted. Under standard air-mass 1.5 global illumination, the open-circuit voltage of solar cells with TiO2 nanocubic modifier was increased from 0.93 V to 1.02 V, and achieved a maximum power conversion efficiency of 14.70% with average value of 13.36%, which is 1.3 times higher than the solar cells based on without modified TiO2 layer (10.44%).
关键词： perovskite,suppress charge recombination,solar cells,interfacial modifier,TiO2 nanocubic
更新于2025-09-16 10:30:52
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Charge photogeneration and recombination in single-material organic solar cells and photodetectors based on conjugated star-shaped donor-acceptor oligomers
摘要： Single-material organic solar cells (SMOSC) are attracted by their simple structure and ease of fabrication so that they are virtually free from a number of drawbacks of heterojunction organic solar cells. However, the performance of SMOSC is still low, first of all because of poor understanding of losses on the way of energy conversion from light to electricity. In this work, we present solution-processed SMOSC based on star-shaped π-conjugated donor-acceptor oligomers with triphenylamine donor (N-Ph3) and alkyl- or phenyl dicyanovinyl acceptor (DCV-R) of general formulae N(Ph-nT-DCV-R)3, where nT stands for n-oligothiophene, and study charge photogeneration and recombination in them. SMOSC demonstrate small energy losses resulting in high open-circuit voltage of 1.08 – 1.19 V and the power conversion efficiency up to 1.22% under illumination intensity of 0.45 sun (1.13% under one sun) with the maximum external quantum efficiency up to 24% for N(Ph-2T-DCV-Ethyl)3, which are among the highest for SMOSC based on conjugated donor-acceptor small molecules or oligomers. It was found that monomolecular recombination dominates at the short-circuit condition and the maximum power point, but at the open-circuit condition the photoinduced charges recombine nearly bimolecularly. The bottleneck in the SMOSC performance was shown to be the field-assisted charge generation perfectly described by the Onsager model in the limit of weak electric fields. The results obtained suggest that intermolecular charge delocalization in conjugated donor-acceptor molecules would be beneficial for further progress in SMOSC.
关键词： conjugated molecule,charge recombination,donor-acceptor molecule,Onsager model,organic solar cell,charge generation
更新于2025-09-12 10:27:22
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Alkyl Group Wrapped Unsymmetrical Squaraine Dyes for Dye-sensitized Solar Cells: Branched Alkyl Chains Modulate the Aggregation of Dyes and Charge Recombination Processes
摘要： Electron transfer processes at the interfaces dictate the factors to improve the photovoltaic parameters such as open-circuit voltage (Voc) and short-circuit current (Jsc) of a dye-sensitized solar cell (DSSC) device besides selecting a set of suitable anode, dye, electrolyte and cathode materials. Inefficient charge injection process at dye-TiO2 interface and charge recombination at the TiO2-dye/electrolyte interface have detrimental effects in improving both Jsc and Voc. Hence tailoring the factors that governs to improve the Jsc and Voc will be an ideal approach to get the desired sensitizers with good device efficiencies. Squaraines are far-red active zwitterionic dyes, has high molar extinction coefficient along with unique aggregation properties due to the larger dipole moment associated with it. Here we report a series of unsymmetrical squaraine dyes, SQS1 to SQS6, with systematic variation of alkyl groups at sp3-C and N-atoms of indoline unit that was away from the anchoring group to control the dye-dye interactions on the TiO2 surface. The branched alkyl groups help to modulate the self-assembly of sensitizers on the TiO2 surface besides passivating the surface that helps to avoid the charge recombination processes. Light harvesting efficiency (LHE) and cyclic voltammetry studies of dye-sensitized TiO2 electrode indicated that the aggregation and charge hopping process between the dye molecules can be modulated, respectively by systematically increasing the number of carbon atoms in the alkyl groups. Such variation in the branched alkyl group helps to enhance the Voc from 672 (SQS1) to 718 mV (SQS6), Jsc from 7.95 (SQS1) to 12.22 mA/cm2 (SQS6), with the device efficiency ranging from 3.82% to 6.23% without any coadsorbent. Dye SQS4 has achieved highest efficiency of 7.1% (Voc = 715 mV, Jsc = 13.05 mA/cm2) with coadsorbent chenodeoxycholic acid (CDCA) using iodine (I-/I3 -) electrolyte compared to its analogs. Analysis of IPCE profile indicates that the major contribution of photocurrent generation is from the aggregated squaraine dyes on TiO2.
关键词： Un-symmetrical squaraines,charge recombination,charge injection,aggregation of dye,dye-sensitized solar cells
更新于2025-09-12 10:27:22
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Impact of PbI <sub/>2</sub> Passivation and Grain Size Engineering in CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> Solar Absorbers as Revealed by Carrier‐Resolved Photo‐Hall Technique
摘要： With power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the Shockley-Queisser limit. One approach for processing enhancement and defect reduction involves additive engineering—, e.g., addition of MASCN (MA = methylammonium) and excess PbI2 have been shown to modify film grain structure and improve performance. However, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. In this study, a newly developed carrier-resolved photo-Hall (CRPH) characterization technique is used that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. CRPH measurements on n-type MAPbI3 films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI2 added to the precursor solution, with little change noted in electron and hole mobility values. Grain size variation (120–2100 nm) and MASCN addition induce no significant change in carrier-related parameters considered, highlighting the benign nature of the grain boundaries and that excess PbI2 must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI3 optoelectronic properties as elucidated by the new CRPH approach.
关键词： photo-Hall characterization,defect passivation,charge carrier transport,perovskites,charge recombination
更新于2025-09-12 10:27:22
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Alkali metal ions passivation to decrease interface defects of perovskite solar cells
摘要： Charge carrier recombination occurring in the interface has become a major hindrance impairing the efficiency and stability of perovskite solar cells (PSCs). Passivation of electronic defects at the surface and grain boundaries is one of the most important strategies to suppress charge recombination and improve crystallization in PSCs. Herein, sodium sulfate (Na2SO4) passivation layer was incorporated into the TiO2/perovskite interface to improve charge transfer. Compared to the devices without Na2SO4, the device with the optimized concentration of Na2SO4 solution exhibits an increased short-circuit current density of 22.83 mA/cm2 and an enhanced fill factor of 73.68%, yielding an increased power conversion efficiency from 15.20% to 18.75%. The efficiency improvement is attributed to the decreased defects and traps as well as the enhanced film crystallization quality.
关键词： Perovskite solar cells,Passivation layer,Surface defects,Charge recombination
更新于2025-09-12 10:27:22
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Precise stress control of inorganic perovskite films for carbon-based solar cells with an ultrahigh voltage of 1.622?V
摘要： All-inorganic cesium lead bromide (CsPbBr3) perovskite solar cell is one promising candidate to balance high efficiency and poor stability of organic-inorganic hybrid photovoltaics. The charge carrier transport can be maximized for high-efficiency devices through precise stress control during perovskite grain growth process to obtain high-quality full-bromine CsPbBr3 halide films. We present here the monolayer-aligned and large-grained CsPbBr3 perovskite films through precise control of crystallization temperature of PbBr2 film because the lattice volume is enlarged by 2.18 times during the phase conversion from PbBr2 to CsPbBr3, which helps to minimize residual-stress-induced grain boundaries and defect-induced charge recombination. Upon further interfacial modification by nitrogen doped carbon quantum dots, the hole transporting materials free, all-inorganic CsPbBr3 perovskite solar cell achieves a champion efficiency as high as 10.71% with an ultrahigh open-circuit voltage of 1.622 V. Moreover, the unencapsulated solar cell demonstrates remarkable long-term stability in 85% humidity in air atmosphere.
关键词： Stability,Strain engineering,Crystal growth,Cesium lead bromide,Charge recombination,Inorganic perovskite solar cell
更新于2025-09-12 10:27:22
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Improved light-harvesting and suppressed charge recombination by introduction of a nanograss-like SnO <sub/>2</sub> interlayer for efficient CdS quantum dot sensitized solar cells
摘要： Quantum dot sensitized solar cell (QDSSC) performance is primarily limited by the recombination of charges at the interfaces of TiO2/quantum dot (QD) sensitizer/electrolyte. Hence, blocking or suppressing the charge recombination is an essential requirement to elevate the QDSSC performance to the next level. To retard the charge recombination, herein, we propose the introduction of a SnO2 nanograss (NG) interlayer on the surface of TiO2 using the facile chemical bath deposition method. The SnO2 NG interlayer not only inhibits the interfacial recombination processes in QDSSCs but also enhances the light-harvesting capability in generating more excitons. Hence, the TiO2/SnO2 NG/CdS QDSSCs can achieve the power conversion efficiency of 3.15%, which is superior to that of a TiO2/CdS device (2.16%). Electrochemical impedance spectroscopy, open-circuit voltage decay and dark current analyses confirm that the photoanode/electrolyte interface is suppressed and the life time is improved by introducing the SnO2 NG interlayer between the TiO2 and CdS QD sensitizer.
关键词： Charge recombination,SnO2 nanograss,Light-harvesting,Chemical bath deposition,Quantum dot sensitized solar cells
更新于2025-09-12 10:27:22
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Significant Influence of a Single Atom Change in Auxiliary Acceptor on Photovoltaic Properties of Porphyrin-Based Dye-Sensitized Solar Cells
摘要： The rational design of porphyrin sensitizers is always crucial for dye-sensitized solar cells (DSSCs), since the change of only a single atom can have a signi?cant in?uence on the photovoltaic performance. We incorporated the pyridothiadiazole group, as a stronger electron-withdrawing group, into the commonly well-established skeleton of D-porphyrin-triple bond-acceptor sensitizers by a single atom change for a well-known strong electron-withdrawing benzothiadiazole (BTD) unit as an auxiliary acceptor. The impact of the pyridothiadiazole group on the optical; electrochemical; and photovoltaic properties of D–π–A porphyrin sensitizers was investigated with comparison for a benzothiadiazole-substituted SGT-020 porphyrin. The pyridothiadiazole-substituted SGT-024 porphyrin dye was red-shifted so that the absorption range might be expected to achieve higher light harvest ef?ciency (LHE) than the SGT-020 porphyrin. However, all the devices were fabricated by utilizing SGT-020 and SGT-024, evaluated and found to achieve a cell ef?ciency of 10.3% for SGT-020-based DSSC but 4.2% for SGT-024-based DSSC under standard global AM 1.5G solar light conditions. The main reason is the lower charge collection ef?ciency of SGT-024-based DSSC than SGT-020-based DSSC, which can be attributed to the tilted dye adsorption mode on the TiO2 photoanode. This may allow for faster charge recombination, which eventually leads to lower Jsc, Voc and power conversion ef?ciency (PCE).
关键词： charge collection ef?ciency,dye-sensitized solar cells,D–π–A structural porphyrin,acceptor units,charge recombination
更新于2025-09-11 14:15:04
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1D Pyrrolidinium Lead Iodide for Efficient and Stable Perovskite Solar Cells
摘要： Due to the superior environmental stability, the utilization of low-dimensional perovskites in organometal halide solar cells (OMHSCs) has been on the sharp increase. Herein, we report a method to in situ form one-dimensional pyrrolidinium lead iodide (1D PyPbI3) atop the photoactive three-dimensional methylammonium lead iodide (3D MAPbI3) using pyrrolidine post-treatment. As compared to the 3D MAPbI3, the 1D PyPbI3 has a wider bandgap and is more environmentally stable, which serves as a tunnelling contact to mitigate charge carrier recombination and robust barrier against environmental degradation when incorporated into OMHSCs. Accordingly, power conversion efficiencies of the resulting MAPbI3 devices were enhanced from an average of 14.86 ± 0.65% to 15.9 ± 0.58% while shelf-life stability was significantly prolonged.
关键词： perovskite solar cell,one-dimensional perovskite,environmental stability,pyrrolidine,photovoltaic performance,pyrrolidinium lead iodide,charge recombination
更新于2025-09-11 14:15:04
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Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells
摘要： In organic solar cells, maximizing the open-circuit voltage (VOC) via minimization of the ionization energy or electron a?nity o?sets of the blended donor and acceptor often comes at the expense of achieving a considerable amount of short-circuit current (JSC). To explore a hypothesis for the design of materials that may circumvent this tradeo?, eight structurally similar polymers were synthesized consisting of a ?uorinated/non-?uorinated benzothiadiazole (BTDF/BTD) strong acceptor moiety, a thiophene ester (TE) weak acceptor, and various donor units composed of bithiophene (T2), biEDOT, and benzodithiophene (BDT) to form six acceptor gradient and two nongradient polymers. The acceptor gradient motif was designed and theorized to induce more facile exciton dissociation in low driving force solar cells by creating a further separated intramolecular charge-transfer state between the strong BTD acceptor and various donor units through a bridging TE component. Solar cells were fabricated using the eight polymers blended with phenyl-C71-butyric-acid methyl ester (PC71BM) to reveal two top performing isomeric polymers, T2-BTDF-(TE2) and TE2-BTDF-(T2), which were further tested with several non-fullerene acceptors (NFAs): EH-IDTBR, ITIC, and ITIC-4F. In order to fabricate optimally performing solar cells, a 0.2 eV ionization energy o?set was found to be essential or the short-circuit current of the NFA cells diminished dramatically. Ultimately, optimized NFA solar cells were fabricated using ITIC-4F paired with each of the top performing polymers to produce an average PCE of 7.3% for TE2-BTDF-(T2) (nongradient) and 3.6% for T2-BTDF-(TE2) (gradient). The acceptor gradient e?ect was not shown to reduce the amount of charge recombination in NFA solar cells mainly due to the inability to fabricate solar cells, with minimal ionization energy or electron a?nity o?sets along with morphological complications. This work stresses the importance of acquiring accurate ionization energies and electron a?nities when characterizing solar cell energetics, as di?erences as small as 0.1 eV in the o?sets can make a signi?cant impact on overall charge collection.
关键词： acceptor gradient polymers,open-circuit voltage,electron affinity offset,charge recombination,organic solar cells,non-fullerene acceptors,ionization energy offset,short-circuit current
更新于2025-09-11 14:15:04