Impact of inkjet printed ZnO electron transport layer on the characteristics of polymer solar cells

Significant Stability Improvement of Fullerene Organic Photovoltaics via ZnO Film Modification through the Intermittent Spray Pyrolysis Technique

Morphological control of the layers within the bulk heterojunction organic photovoltaics (BHJ-OPVs) is a key feature that governs their performance. In the present work, we demonstrate that zinc oxide-ZnO-interlayers sprayed via the intermittent spray pyrolysis technique, employing a low-concentration precursor solution, can yield inverted BHJ-OPVs as efficient as the standard reported ones using the conventional laboratory-scale spin-coating technique. However, we record a pioneer stability behavior of the fabricated inverted fullerene organic photovoltaics (iF-OPVs) with various sprayed ZnO conditions. Thus, after optimizing the sprayed ZnO interfacial layer morphology for the inverted PTB7-Th:PC₇₀BM devices, by carefully inspecting the interdependence between the sprayed ZnO thin film morphology and the figures of merit of the optimized iF-OPVs, we conducted a distinct analysis on the optical and electronic properties of the fresh and degraded devices using external quantum efficiency measurements and impedance spectroscopy. Hence, we showed that the most proper ZnO microstructural morphology was obtained by spraying 25 running cycles (25R). Remarkably, we observed that 25R-ZnO-based iF-OPV devices showed a stunning stability behavior and maintained 85% of their initial power conversion efficiency even after 16.7 months without encapsulation in a dry nitrogen glovebox, demonstrating an excellent shelf stability. Accordingly, this approach might facilitate the scalability of inverted OPVs for industrial production visibility.

Fluorinated Zinc and Copper Phthalocyanines as Efficient Third Components in Ternary Bulk Heterojunction Solar Cells

Fluorinated zinc and copper metallophthalocyanines MPcF₄₈ are synthesized and incorporated as third component small molecules in ternary organic solar cells (TOSCs). To enable the high performance of TOSCs, maximizing short-circuit current density (J _SC) is crucial. Ternary bulk heterojunction blends, consisting of a polymer donor PTB7-Th, fullerene acceptors PC₇₀BM, and a third component MPcF₄₈, are formulated to fabricate TOSCs with a device architecture of ITO/PFN/active layer/V₂O₅/Ag. Employing copper as metal atom substitution in the third component of TOSCs enhances J _SC as a result of complementary absorption spectra in the near-infrared region. In combination with J _SC enhancement, suppressed charge recombination, improved exciton dissociation and charge carrier collection efficiency, and better morphology lead to a slightly improved fill factor (FF), resulting in a 7% enhancement of PCE than those of binary OSCs. In addition to the increased PCE, the photostability of TOSCs has also been improved by the appropriate addition of CuPcF₄₈. Detailed studies imply that metal atom substitution in phthalocyanines is an effective way to improve J _SC, FF, and thus the performance and photostability of TOSCs.

Effect of the Agglomerate Geometry on the Effective Electrical Conductivity of a Porous Electrode

The study of the microstructure of random heterogeneous materials, related to an electrochemical device, is relevant because their effective macroscopic properties, e.g., electrical or proton conductivity, are a function of their effective transport coefficients (ETC). The magnitude of ETC depends on the distribution and properties of the material phase. In this work, an algorithm is developed to generate stochastic two-phase (binary) image configurations with multiple geometries and polydispersed particle sizes. The recognizable geometry in the images is represented by the white phase dispersed and characterized by statistical descriptors (two-point and line-path correlation functions). Percolation is obtained for the geometries by identifying an infinite cluster to guarantee the connection between the edges of the microstructures. Finally, the finite volume method is used to determine the ETC. Agglomerate phase results show that the geometry with the highest local current distribution is the triangular geometry. In the matrix phase, the most significant results are obtained by circular geometry, while the lowest is obtained by the 3-sided polygon. The proposed methodology allows to establish criteria based on percolation and surface fraction to assure effective electrical conduction according to their geometric distribution; results provide an insight for the microstructure development with high projection to be used to improve the electrode of a Membrane Electrode Assembly (MEA).

Subphthalocyanine-Diketopyrrolopyrrole Conjugates: 3D Star-Shaped Systems as Non-Fullerene Acceptors in Polymer Solar Cells with High Open-Circuit Voltage

Four star-shaped electron acceptors (C1 -OPh, C3 -OPh, C1 -Cl and C3 -Cl) based on a subphthalocyanine core bearing three diketopyrrolopyrrole wings linked by an acetylene bridge have been synthesized. These derivatives feature two different axial substituents (i. e., 4-tert-butylphenoxy (OPh) or chlorine (Cl)) and for each of them, both the C1 and the C3 regioisomers have been investigated. The four compounds exhibit a broad absorption band in the 450-700 nm region, with bandgap values near to 2 eV. These materials were applied in the active layer of inverted bulk-heterojunction polymer solar cells in combination with the donor polymer PBDB-T. Derivatives bearing the OPh axial group showed the best performances, with C1 -OPh being the most promising with a PCE of 3.27 % and a Voc as high as 1.17 V. Despite presenting the widest absorption range, the photovoltaic results obtained with C1 -Cl turned out to be the lowest (PCE=1.01 %).

Printing ZnO Inks: From Principles to Devices

Solution-based printing approaches permit digital designs to be converted into physical objects by depositing materials in a layer-by-layer additive fashion from microscale to nanoscale resolution. The extraordinary adaptability of this technology to different inks and substrates has received substantial interest in the recent literature. In such a context, this review specifically focuses on the realization of inks for the deposition of ZnO, a well-known wide bandgap semiconductor inorganic material showing an impressive number of applications in electronic, optoelectronic, and piezoelectric devices. Herein, we present an updated review of the latest advancements on the ink formulations and printing techniques for ZnO-based nanocrystalline inks, as well as of the major applications which have been demonstrated. The most relevant ink-processing conditions so far explored will be correlated with the resulting film morphologies, showing the possibility to tune the ZnO ink composition to achieve facile, versatile, and scalable fabrication of devices of different natures.

On-Substrate Joule Effect Heating by Printed Micro-Heater for the Preparation of ZnO Semiconductor Thin Film

Fabrication of printed electronic devices along with other parts such as supporting structures is a major problem in modern additive fabrication. Solution-based inkjet printing of metal oxide semiconductor usually requires a heat treatment step to facilitate the formation of target material. The employment of external furnace introduces additional complexity in the fabrication scheme, which is supposed to be simplified by the additive manufacturing process. This work presents the fabrication and utilization of micro-heater on the same thermal resistive substrate with the printed precursor pattern to facilitate the formation of zinc oxide (ZnO) semiconductor. The ultraviolet (UV) photodetector fabricated by the proposed scheme was successfully demonstrated. The performance characterization of the printed devices shows that increasing input heating power can effectively improve the electrical properties owing to a better formation of ZnO. The proposed approach using the on-substrate heating element could be useful for the additive manufacturing of functional material by eliminating the necessity of external heating equipment, and it allows in-situ annealing for the printed semiconductor. Hence, the integration of the printed electronic device with printing processes of other materials could be made possible.