arXiv subjects

Jaime Martín

Publications and source records attributed to Jaime Martín.

7 recordsLinked to original sources

arXiv2026

Exploring the Potential of Ternary Blending for Two and Three-Junction RAINBOW Solar Cells

The efficiency of organic photovoltaics (OPV) has been steadily increasing over the past decade until reaching the 20\% milestone. Multijunction architectures provide a promising approach to further enhance performance. Here we explore the potential of a spectral splitting geometry, referred to as RAINBOW, in which subcells are placed side-by-side and externally connected, thus minimizing the fabrication and current matching challenges found in vertically stacked configurations. First, we tested 7 different binaries with bandgaps spanning from 1.98 to 1.16 eV. The systems with the widest and narrowest gaps suffered greater losses and so we evaluate if ternary mixing could help to overcome these limitations by evaluating 5 different ternaries. Generally speaking, ternary mixing tunes the Voc, and when morphology and energy levels are well aligned, the overall PCE can be boosted in the spectral region where the subcell should absorb, as is the case for PTB7-Th:COTIC-4F:BTP-eC9 when operating as red subcell. Device simulations help to identify the 2-junction and 3-junction configurations with highest PCEs, all of which include ternaries. We fabricate proof-of-concept RAINBOW devices using scalable methods in which the subcells are deposited by meniscus-guided blade coating. The efficiency improves from 12.9\% in single-junction devices to 15.9\% in 2-junction devices (16.4\% in simulations) and 17.3\% in 3-junction devices (17.7\% in simulations), confirming the viability of the RAINBOW architecture for scalable, high-efficiency OPVs. Finally, detailed balance analysis indicates that the potential of this geometry can be very high provided that high efficiency wide bandgap (2-2.5 eV) materials become available.

cond-mat.mtrl-sci↗

arXiv2017

Manipulating Semicrystalline Polymers in Confinement

Because final properties of nanoscale polymeric structures are largely determined by the solid-state microstructure of the confined polymer, it is imperative not only to understand how the microstructure of polymers develops under nanoscale confinement but also to establish means to manipulate it. Here we present a series of processing strategies, adapted from methods used in bulk polymer processing, that allow to control the solidification of polymer nanostructures. Firstly, we show that supramolecular nucleating agents can be readily used to modify the crystallization kinetics of confined poly(vinylidene fluoride) (PVDF). In addition, we demonstrate that microstructural features that are not traditionally affected by nucleating agents, such as the orientation of crystals, can be tuned with the crystallization temperature applied. Interestingly, we also show that high crystallization temperatures and long annealing periods induce the formation of the modification of PVDF, hence enabling the simple production of ferro/piezoelectric nanostructures. We anticipate that the approaches presented here can open up a plethora of new possibilities for the processing of polymer-based nanostructures with tailored properties and functionalities.

cond-mat.mtrl-sci↗

arXiv2017

Solid-state-processing of d_PVDF

Poly(vinylidene fluoride) (PVDF) has long been regarded as an ideal piezoelectric plastic because it exhibits a large piezoelectric response and a high thermal stability. However, the realization of piezoelectric PVDF elements has proven to be problematic, amongst others, due to the lack of industrially-scalable methods to process PVDF into the appropriate polar crystalline forms. Here, we show that fully piezoelectric PVDF films can be produced via a single-step process that exploits the fact that PVDF can be molded at temperatures below its melting temperature, i.e. via solid-state-processing. We demonstrate that we thereby produce d_PVDF, the piezoelectric charge coefficient of which is comparable to that of biaxially stretched d_PVDF. We expect that the simplicity and scalability of solid-state processing combined with the excellent piezoelectric properties of our PVDF structures will provide new opportunities for this commodity polymer and will open a range of possibilities for future, large-scale, industrial production of plastic piezoelectric films

cond-mat.mtrl-sci↗

arXiv2017

Synthesis and properties of a novel narrow band gap oligomeric diketopyrrolopyrrole-based organic semiconductor

An oligomeric semiconductor containing three bisthiophenediketopyrrolopyrole units (Tri-BTDPP) was synthesized and characterized. Tri-BTDPP has a HOMO level of -5.34 eV, a broad absorption close to the near infrared region and a low band gap of 1.33 eV. Additionally, a promising hole mobility of 1 x 10-3 cm V-1 s-1 was achieved after thermal annealing at 150 C in organic field effect transistors (OFET). Organic photovoltaic (OPV) cells containing Tri-BTDPP and PC71BM as the donor/acceptor couple exhibited a power conversion efficiency (PCE) of 0.72%. Through an intensive study of the active layer using AFM, XRD, and DSC, it was found that Tri-BTDPP and PC71BM were unable to intermix effectively, resulting in oversized Tri-BTDPP crystalline phases and thus poor charge separation. Strategies to improve the OPV performance were thus proposed.

cond-mat.mtrl-sci↗

arXiv2017

New 3,3'-(ethane-1, 2-diylidene)bis(indolin-2-one) (EBI)-based small molecule semiconductors for organic solar cells

A series of donor-acceptor-donor (D-A-D) structured small-molecule compounds, with 3,3'-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI) as a novel electron acceptor building block coupled with various electron donor end-capping moieties (thiophene, bithiophene and benzofuran), were synthesized and characterized. When the fused-ring benzofuran is combined to EBI (EBI-BF), the molecules displayed a perfectly planar conformation and afforded the best charge tranport properties among these EBI compounds with a hole mobility of up to 0.021 cm2 V-1 s-1. All EBI-based small molecules were used as donor material along with a PC61BM acceptor for the fabrication of solution-processed bulk-heterojunction (BHJ) solar cells. The best performing photovoltaic devices are based on the EBI derivative using the bithiophene end-capping moiety (EBI-2T) with a maximum power conversion efficiency (PCE) of 1.92%, owing to the broad absorption spectra of EBI-2T and the appropriate morphology of the BHJ. With the aim of establishing a correlation between the molecular structure and the thin film morphology, differential scanning calorimetry, atomic force microscopy and X-ray diffraction analysis were performed on neat and blend films of each material.

cond-mat.mtrl-sci↗

arXiv2017

Confinement Effects on the Crystalline Features of Poly(9,9-dioctylfluorene)

Typical device architectures in polymer-based optoelectronic devices, such as field effect transistors organic light emitting diodes and photovoltaic cells include sub-100 nm semiconducting polymer thin-film active layers, whose microstructure is likely to be subject to finite-size effects. The aim of this study was to investigate effect of the two-dimensional spatial confinement on the internal structure of the semiconducting polymer poly(9,9-dioctylfluorene) (PFO). PFO melts were confined inside the cylindrical nanopores of anodic aluminium oxide (AAO) templates and crystallized via two crystallization strategies, namely, in the presence or in the absence of a surface bulk reservoir located at the template surface. We show that highly textured semiconducting nanowires with tuneable crystal orientation can be thus produced. Moreover, our results indicate that employing the appropriate crystallization conditions extended-chain crystals can be formed in confinement. The results presented here demonstrate the simple fabrication and crystal engineering of ordered arrays of PFO nanowires; a system with potential applications in devices where anisotropic optical properties are required, such as polarized electroluminescence, waveguiding, optical switching, lasing, etc.

cond-mat.mtrl-sci↗

arXiv2016

Optically lightweight tracking of objects around a corner

The observation of objects located in inaccessible regions is a recurring challenge in a wide variety of important applications. Recent work has shown that indirect diffuse light reflections can be used to reconstruct objects and two-dimensional (2D) patterns around a corner. However, these prior methods always require some specialized setup involving either ultrafast detectors or narrowband light sources. Here we show that occluded objects can be tracked in real time using a standard 2D camera and a laser pointer. Unlike previous methods based on the backprojection approach, we formulate the problem in an analysis-by-synthesis sense. By repeatedly simulating light transport through the scene, we determine the set of object parameters that most closely fits the measured intensity distribution. We experimentally demonstrate that this approach is capable of following the translation of unknown objects, and translation and orientation of a known object, in real time.

cs.CV↗