Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells.

The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.We thank the EPSRC (EP/H040218 and EP/I019278) for financial support

A Novel Alkylated Indacenodithieno[3,2-b]thiophene-based Polymer for Highperformance

<p>A novel rigid donor monomer, indacenodithieno[3,2-b]thiophene (IDTT), containing linear<br>alkyl chains is reported. Co-polymers of IDTT with the acceptor benzothiadiazole (BT) is<br>shown to be excellent p-type semiconductors in organic field effect transistors (OFET).<br>Devices based upon conventional top gate architectures with pentafluorobenzenethiol<br>modified Au electrodes exhibited a hole mobility up to 6.6 cm2V-1s-1 after thermal annealing.<br>We also demonstrate for the first time that treatment of the electrodes with solution deposited<br>copper(I) thiocyanate (CuSCN) interfacial layer has a beneficial hole injection/electron<br>blocking effect, further enhancing mobility to 8.7 cm2V-1s-1.</p

An Alternating 5,5-Dimethylcyclopentadiene and Diketopyrrolopyrrole Copolymer prepared at Room Temperature for High Performance Organic Thin-Film Transistors

We report that the inclusion of non-aromatic 5,5-dimethylcyclopentadiene monomer into a conjugated backbone is an attractive strategy to high performance semiconducting polymers. The use of this monomer enables a room temperature Suzuki copolymerization with a diketopyrrolopyrrole comonomer to afford a highly soluble, high molecular weight material. The resulting low band gap polymer exhibits excellent photo and thermal stability, and despite a large π-π stacking distance of 4.26 Å, it demonstrates excellent performance in thin-film transistor devices

Alkylated selenophene-based ladder-type monomers via a facile route for high performance thin-film transistor applications

We report the synthesis of two new selenophene containing ladder-type monomers, cyclopentadiselenophene and (CDS) and indacenodiselenophene (IDSe), via a facile route. Co-polymers with benzothiadiazole (BT) were prepared in high yield by Suzuki polymerization to afford co-polymers which exhibited excellent solubility in a range of non-chlorinated solvents.Thin-film transistors were fabricated using environmentally benign, non-chlorinated solvents with the CDS and IDSe co-polymers exhibiting hole mobility up to 0.15 and 6.4 cm²/Vs, respectively

Alkylated indacenodithieno[3,2-b]thiophene-based all donor ladder-type conjugated polymers for organic thin film transistors

We report the synthesis of a series of indacenodithieno[3,2-b]thiophene (IDTT) based conjugated polymers by copolymerization with three different electron rich co-monomers [thiophene (T), thieno[3,2-b]thiophene (TT) and dithieno[3,2-b:2,3-d]thiophene (DTT)] under Stille coupling conditions. The resulting all donor polymeys show very good solubility in common solvents and exhibit similar optical, thermal and electronic properties. However, the performance of these semiconductors in thin film transistor devices varied and was highly dependent on the nature of the co-mnomer. All polymers exhibited unipolar p-type charge transport behaviour, with the mobility values following the trend of IDTT-TT>IDTT-DTT>IDTT-T. The peak saturation mobility value of IDTT-TT was extracted to be 1.1 cm2V-1s-1, amongst the highest mobilty for all-donor conjugated poymers reported to data<br

Predicting the photocurrent–composition dependence in organic solar cells

Dataset complementario en Digital.CSIC: https://digital.csic.es/handle/10261/223231 (10.20350/digitalCSIC/12719)The continuous development of improved non-fullerene acceptors and deeper knowledge of the fundamental mechanisms governing performance underpin the vertiginous increase in efficiency witnessed by organic photovoltaics. While the influence of parameters like film thickness and morphology are generally understood, what determines the strong dependence of the photocurrent on the donor and acceptor fractions remains elusive. Here we approach this problem by training artificial intelligence algorithms with self-consistent datasets consisting of thousands of data points obtained by high-throughput evaluation methods. Two ensemble learning methods are implemented, namely a Bayesian machine scientist and a random decision forest. While the former demonstrates large descriptive power to complement the experimental high-throughput screening, the latter is found to predict with excellent accuracy the photocurrent–composition phase space for material systems outside the training set. Interestingly, we identify highly predictive models that only employ the materials band gaps, thus largely simplifying the rationale of the photocurrent–composition space.This work was supported by the Spanish Ministerio de Ciencia e Innovación under Grants PGC2018-095411-B-I00, FIS2016-78904-C3-1-P, and SEV-2015-0496 in the framework of the Spanish Severo Ochoa Centre of Excellence. We acknowledge financial support from the European Research Council through project ERC CoG 648901 and the H2020 Marie Curie actions through the SEPOMO project (grant number 722651). X. R.-M., E. P.-S.-J. and M. C.-Q. thank Dr Bernhard Dörling for designing the doctor blade controller and Mr Martí Gibert-Roca for designing the multiplexer/switcher. X. R.-M. acknowledges the departments of Physics, Chemistry and Geology of the Autonomous University of Barcelona (UAB) as coordinators of the PhD program in Materials Science. M. H. acknowledges the Royal Society and the Wolfson Foundation. The authors thank Dr Mathieu Linares and Dr Jasper Michels for inspiring discussions at the early stages of this work. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe