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Role of Molecular and Interchain Ordering in the Formation of a δ-Hole Transporting Layer in Organic Solar Cells
摘要： Interface engineering, especially the realisation of ohmic contacts at the interface between organic semiconductors and metal contacts, is one of the essential preconditions to achieve high efficiency organic electronic devices. Here, the interface structure of polymer/fullerene blends are correlated with the charge extraction/injection properties of working organic solar cells. The model system – P3HT:PCBM – is fabricated using two different degrees of P3HT regioregularity to alter the blend interchain order and molecular packing, resulting in different device performance. Investigations by electroabsorption (EA) spectroscopy on these devices indicate a significant reduction (≈ 1 V) in the built-in potential with an increase in the P3HT regioregularity. This observation is also supported by a change in the WF of high regioregular polymer blends from photoelectron spectroscopy measurement. These results confirm the presence of a strong dipole layer acting as a δ-hole transporting layer at the polymer/MoO3/Ag electrode interface. Unipolar hole-only devices show an increase in the magnitude of the hole current in high regioregular P3HT devices, suggesting an increase in the hole injection/extraction efficiency inside device with a δ-hole transporting layer. Microscopically, near edge X-ray absorption fine structure (NEXAFS) spectroscopy was conducted to probe the surface microstructure in these blends finding a highly edge-on orientation of P3HT chains in blends made with high regioregular P3HT. This edge-on orientation of P3HT chains at the interface results in a layer of oriented alkyl side chains capping the surface which favors the formation of a dipole layer at the polymer/MoO3 interface. The increase in the charge extraction efficiency due to the formation of a δ-hole transporting layer thus results in higher short circuit currents and fill factor values, eventually increasing the device efficiency in high regioregular P3HT devices despite a slight decrease in cell open circuit voltage. These findings emphasise the significance of work function control as a tool for improved device performance, and pave the way towards interfacial optimisation based on the modulation of fundamental polymer properties, such as polymer regioregularity.
关键词： Organic solar cells,interface engineering,molecular ordering,regioregularity,interface dipole,interchain ordering,P3HT
更新于2025-09-12 10:27:22
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A Comparison Between Functions of Carbon Nanotube and Reduced Graphene Oxide and Respective Ameliorated Derivatives in Perovskite Solar Cells
摘要： The reduced graphene oxide (rGO) and carbon nanotube (CNT) components and their derivatives grafted with the irregioregular poly(3-dodecyl thiophene) (rGO-g-PDDT and CNT-g-PDDT) and regioregular poly(3-hexylthiophene) (CNT-g-P3HT and CNT-g-P3HT) polymers were used to improve the morphological, optical, and photovoltaic features of CH3NH3PbI3 perovskite solar cells. The type of carbonic material (CNT or rGO) and regioregularity of grafts affected the cell performances. According to the photoluminescence lifetimes, although the grafted-CNT/rGO components improved the cell characteristics (15.3-20.5 ns), the corresponding bared nanostructures ruined them (3.0-4.9 ns). In similar conditions, via alteration of rGO to CNT, the average cell performance changed to 14.56 from 14.07% for PDDT-grafted systems and to 16.36 from 15.15% for P3HT-based ones. The self-ordering polymers such as regioregular P3HTs simultaneously induced the crystallinity to the polymeric and non-polymeric constituents. The best photovoltaic data including 22.73 mA/cm2, 75%, 0.96 V and 16.36% with the narrowest distributions were detected in the CH3NH3PbI3 + CNT-g-P3HT solar cells. Perovskite solar cells were perfectly modified with both rGO-g-P3HT and CNT-g-P3HT agents because of the lowest charge-transfer resistance values (93.2 and 90.1 Ω), the most intensified crystalline peaks, and the largest absorbances.
关键词： morphology,regioregularity,CNT,rGO,perovskite
更新于2025-09-11 14:15:04
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Regioregularity and Electron Deficiency Control of Unsymmetric Diketopyrrolopyrrole Copolymers for Organic Photovoltaics
摘要： Manipulating the electron deficiency and controlling the regioregularity of π-conjugated polymers are important for the fine-tuning of their electronic and electrochemical properties to make them suitable for an organic solar cell. Here, we report such a molecular design of unsymmetric diketopyrrolopyrrole (DPP) based copolymers with different aromatic side units of either thiophene (Th), pyridine (Py), or fluorobenzene (FBz). The unsymmetric electron acceptors of Th?DPP?Py and Th?DPP?FBz were polymerized with the electron donor of two-dimensional benzobisthiophene (BDT-Th), affording two regiorandom DPP copolymers. They exhibited contrasting molecular orbital levels and bulk heterojunction morphology in methanofullerene-blended films, leading to power conversion efficiencies of 3.75 and 0.18%, respectively. We further synthesized a regioregular DPP copolymer via sandwiching the centrosymmetric BDT-Th unit by two Th?DPP?Py units in an axisymmetric manner. The extensive characterization through morphology observation, X-ray diffraction, and space-charge-limited current mobilities highlight the case-dependent positive/negative effects of regioregularity and electron deficiency control.
关键词： diketopyrrolopyrrole,organic photovoltaics,electron deficiency,regioregularity,power conversion efficiency
更新于2025-09-11 14:15:04