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Understanding the effect of solvent additive in polymeric thin film: turning a bilayer in a bulk heterojunction like photovoltaic device
摘要： Here we report the effect of an additive solvent, the 1,8-diiodooctane (DIO) on the performance of a bilayer organic photovoltaic (OPV) device which active layer comprises the poly[2,7-(9,9-bis(2 ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material and C60 as the electron acceptor material. We observed that when the donor layer was treated with 1% of DIO the power conversion efficiency (PCE) of the device increase 138.4% in relation to the device with a non-treated donor layer and 21.3% in relation to the device containing a donor layer submitted to a thermal annealed. The main effects that lead to this increase in PCE are the large interfacial area between donor and acceptor materials and the improved conductivity at low voltages. The increase in polymer surface roughness leads to a more effective PSiF-DBT/C60 interface for exciton dissociation. This effect, as well as the increase in the conductivity, raised the short circuit current density (JSC) to 13.89 mA/cm2 and PCE to 4.84%. Our conclusions are supported by morphological analysis, chemical cross-sectional evaluations with advanced microscopy techniques, charge mobility measurements as well as by theoretical simulations of the devices in which the changes on the donor/acceptor interfacial area were considered. The outcomes suggest that, solvent additives could be an alternative treatment to replace the thermal annealing which imposes further difficulties to perform the lab-to-manufacturing upscaling.
关键词： solvent additive,PSiF-DBT,exciton dissociation,1,8-diiodooctane,C60,organic photovoltaic,power conversion efficiency
更新于2025-09-23 15:21:01
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The Phase Behavior in the Active Layer of Small Molecule Organic Photovoltaics: The State Diagram of p-DTS(FBTTh <sub/>2</sub> ) <sub/>2</sub> :PC <sub/>71</sub> BM
摘要： A comprehensive study was undertaken to obtain a more fundamental understanding of the phase behavior of the p-DTS(FBTTh2)2:PC71BM system, used in small molecule organic solar cells, with a strong focus on the amorphous phase and its influence on crystallinity. Three dedicated thermal protocols were used in combination with advanced thermal analysis, solid-state NMR, and wide angle X-ray diffraction. Rapid cooling, to avoid structure formation and gain insight in the amorphous phase, and slow cooling, to promote structure formation, were used as limiting cases to explain the intermediate behavior after device processing from solution. A complete state diagram was developed and the glass transition (Tg) - composition relationship was determined. In the case of slow cooling and the procedure used for device processing, the rapid crystallization of p-DTS(FBTTh2)2 leads to an enrichment of the amorphous phase in PC71BM, increasing its Tg and causing vitrification of the mixed amorphous phase before crystallization when the total amount of PC71BM exceeds 70 wt%. The common processing additive 1,8-diiodooctane (DIO) was found to lead to a lower p-DTS(FBTTh2)2 crystallinity and smaller average crystal size. More importantly, it acts as a strong plasticizer, lowering Tg significantly and thus reducing the morphological stability of the p-DTS(FBTTh2)2:PC71BM mixtures.
关键词： p-DTS(FBTTh2)2:PC71BM,glass transition temperature,wide angle X-ray diffraction,phase behavior,crystallinity,amorphous phase,small molecule organic photovoltaics,thermal analysis,solid-state NMR,1,8-diiodooctane (DIO)
更新于2025-09-23 15:19:57
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Exploring chemical interaction between Diiodooctane and PEDOT-PSS electrode for metal electrode-free non-fullerene organic solar cells
摘要： Metal electrode-free organic solar cells with printable top electrode are attractive to realize the low cost of photovoltaics. Interaction between the printable electrode and active layer is critical to the device performance. In this work, we report on chemical interaction between printable polymer electrode poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and typically used additive of 1,8-Dioodooctane (DIO) in active layer. DIO can be converted to HI under the acidic condition of PEDOT:PSS, and the HI chemically reduces the PEDOT:PSS with the appearance of absorbance band at 800-1100 nm. The generation of I2 is verified by the color change of starch. The reaction results in decrease of its work function that hinders the efficient hole collection. A strategy is proposed to circumvent the detrimental interaction by inserting an ultrathin (15 nm) active layer without DIO between the initial active layer and PEDOT:PSS electrode. A power conversion efficiency (PCE) of 10.1% is achieved for the metal electrode-free non-fullerene organic solar cells.
关键词： PEDOT:PSS,1,8-Diiodooctane,chemical interaction,water transfer printing,organic solar cell,non-fullerene
更新于2025-09-12 10:27:22
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Revealing Hidden UV Instabilities in Organic Solar Cells by Correlating Device and Material Stability
摘要： With state-of-the-art organic solar cells (OSCs) surpassing 16% efficiency, stability becomes critical for commercialization. In this work, the power of using photoluminescence (PL) measurements on plain films is demonstrated, as well as high-performance liquid chromatography analysis to reveal the origin of UV instabilities in OSCs based on the most commonly used acceptors PC70BM ([6,6]-phenyl-C71-butyric acid methyl ester), ITIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene), and o-IDTBR (indacenodithiophene-based non-fullerene acceptor). The UV dependent stability tests reveal instabilities in solar cells based on PC70BM and ITIC while devices based on o-IDTBR are highly stable even under UV illumination. The analysis of solar cell devices based on charge extraction and sub-bandgap external quantum efficiency only shows the UV-dependent emergence of traps, while PL spectra of plain films on glass allows the disentanglement and identification of individual instabilities in multi-component bulk-heterojunction devices. In particular, the PL analysis demonstrates UV instabilities of PC70BM and ITIC toward the processing additive 1,8 diiodooctane (DIO). The chemical analysis reveals the in-depth mechanism, by providing direct proof of photochemical reactions of PC70BM and ITIC with UV-induced radicals of DIO. Based on this scientific understanding, it is shown how to stabilize PBQ-QF:PC70BM devices.
关键词： degradation,stability,organic solar cells,diiodooctane,UV
更新于2025-09-11 14:15:04