Layer-by-layer all-transfer-based organic solar cells

Over 14% Efficiency Folding-Flexible ITO-free Organic Solar Cells Enabled by Eco-friendly Acid-Processed Electrodes

Environment-friendly manufacturing and mechanical robustness are imperative for commercialization of flexible OSCs as green-energy source, especially in portable and wearable self-powered flexible electronics. Although, the commonly adopted PEDOT:PSS electrodes that are treated with severely corrosive and harmful acid lack foldability. Herein, efficient folding-flexible OSCs with highly conductive and foldable PEDOT:PSS electrodes processed with eco-friendly cost-effective acid and polyhydroxy compound are demonstrated. The acid treatment endows PEDOT:PSS electrodes with high conductivity. Meanwhile, polyhydroxy compound doping contributes to excellent bending flexibility and foldability due to the better film adhesion between PEDOT:PSS and PET substrate. Accordingly, folding-flexible OSCs with high efficiency of 14.17% were achieved. After 1,000 bending or folding cycles, the device retained over 90% or 80% of its initial efficiency, respectively. These results represent one of the best performances for ITO-free flexible OSC reported so far and demonstrate a novel approach toward commercialized efficient and foldable green-processed OSCs.

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Highly conductive PEDOT:PSS electrodes based on eco-friendly acid were exploited

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14.17% folding-flexible organic solar cells were realized

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The bending performance was significantly improved by interface bonding engineering

Magnetically Powered Shape-Transformable Liquid Metal Micromotors

Shape-transformable liquid metal (LM) micromachines have attracted the attention of the scientific community over the past 5 years, but the inconvenience of transfer routes and the use of corrosive fuels have limited their potential applications. In this work, a shape-transformable LM micromotor that is fabricated by a simple, versatile ice-assisted transfer printing method is demonstrated, in which an ice layer is employed as a "sacrificial" substrate that can enable the direct transfer of LM micromotors to arbitrary target substrates conveniently. The resulting LM microswimmers display efficient propulsion of over 60 µm s^-1 (≈3 bodylength s^-1 ) under elliptically polarized magnetic fields, comparable to that of the common magnetic micro/nanomotors with rigid bodies. Moreover, these LM micromotors can undergo dramatic morphological transformation in an aqueous environment under the irradiation of an alternating magnetic field. The ability to transform the shape and efficiently propel LM microswimmers holds great promise for chemical sensing, controlled cargo transport, materials science, and even artificial intelligence in ways that are not possible with rigid-bodies microrobots.

Fabrication Processes to Generate Concentration Gradients in Polymer Solar Cell Active Layers

Polymer solar cells (PSCs) are considered as one of the most promising low-cost alternatives for renewable energy production with devices now reaching power conversion efficiencies (PCEs) above the milestone value of 10%. These enhanced performances were achieved by developing new electron-donor (ED) and electron-acceptor (EA) materials as well as finding the adequate morphologies in either bulk heterojunction or sequentially deposited active layers. In particular, producing adequate vertical concentration gradients with higher concentrations of ED and EA close to the anode and cathode, respectively, results in an improved charge collection and consequently higher photovoltaic parameters such as the fill factor. In this review, we relate processes to generate active layers with ED–EA vertical concentration gradients. After summarizing the formation of such concentration gradients in single layer active layers through processes such as annealing or additives, we will verify that sequential deposition of multilayered active layers can be an efficient approach to remarkably increase the fill factor and PCE of PSCs. In fact, applying this challenging approach to fabricate inverted architecture PSCs has the potential to generate low-cost, high efficiency and stable devices, which may revolutionize worldwide energy demand and/or help develop next generation devices such as semi-transparent photovoltaic windows.

Highly Efficient Organic Solar Cells Consisting of Double Bulk Heterojunction Layers

An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers. Such devices allow a large gain in photocurrent to be obtained due to enhanced photoharvest, without suffering much from the fill factor drop usually seen in thick-layer-based devices. Overall, double-BHJ OSC with optimal ≈50 nm near-infrared PDPP3T:PC₇₁ BM layer atop of ≈200 nm PTB7-Th:PC₇₁ BM BHJ results in high power conversion efficiencies over 12%.

Transfer-printing of active layers to achieve high quality interfaces in sequentially deposited multilayer inverted polymer solar cells fabricated in air

Polymer solar cells (PSCs) are greatly influenced by both the vertical concentration gradient in the active layer and the quality of the various interfaces. To achieve vertical concentration gradients in inverted PSCs, a sequential deposition approach is necessary. However, a direct approach to sequential deposition by spin-coating results in partial dissolution of the underlying layers which decreases the control over the process and results in not well-defined interfaces. Here, we demonstrate that by using a transfer-printing process based on polydimethylsiloxane (PDMS) stamps we can obtain increased control over the thickness of the various layers while at the same time increasing the quality of the interfaces and the overall concentration gradient within the active layer of PSCs prepared in air. To optimize the process and understand the influence of various interlayers, our approach is based on surface free energy, spreading parameters and work of adhesion calculations. The key parameter presented here is the insertion of high quality hole transporting and electron transporting layers, respectively above and underneath the active layer of the inverted structure PSC which not only facilitates the transfer process but also induces the adequate vertical concentration gradient in the device to facilitate charge extraction. The resulting non-encapsulated devices (active layer prepared in air) demonstrate over 40% increase in power conversion efficiency with respect to the reference spin-coated inverted PSCs.

Morphology fixing agent for [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) in planar-type perovskite solar cells for enhanced stability

Enhanced stability of planar-type perovskite solar cells (PSCs) has been demonstrated by applying titanium oxide (TiO_x) interlayer which acts as a morphological fixing agent for preseving delamication of PC₆₀BM with long-term device operation.

Enhanced performance and stability of polymer BHJ photovoltaic devices from dry transfer of PEDOT:PSS

Polymer solar cells with enhanced initial cell performances and long-term stability were fabricated by performing a simple dry transfer of a hole extraction layer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] onto an indium tin oxide (ITO) substrate. Due to the very flat surface of the polyurethane acrylate/polycarbonate (PUA/PC) film, which was used as a mold and resembled the surface of the original substrate (silicon wafer), the transferred layer had a very smooth surface morphology, resulting in enhancement of the interfacial characteristics. The work function of the PEDOT:PSS layer and the morphology of bulk hetero junction (BHJ) layer were tuned by controlling the position of PSS enrichment in the PEDOT:PSS layer using the dry transfer. The power conversion efficiency of PTB7:PC71 BM BHJ device prepared by the dry transfer was 8.06%, which was significantly higher than that of the spin-cast device (7.32%). By avoiding direct contact between the ITO substrate and the PEDOT:PSS solution in the dry transfer system, etching and diffusion of indium in the ITO substrate were greatly reduced, thereby improving the stability.