Panagiotis E. Keivanidis

Cyprus University of Technology · Department of Mechanical and Materials Science and Engineering

Bimolecular processes involving exciton spin-state interactions gain attention for their deployment as wavelength-shifting tools. Particularly triplet-triplet annihilation induced photon energy up-conversion (TTA-UC) holds promise to enhance the performance of solar...

Solution-processable dopants are popular wet-lab mediators to engineer the electronic properties of organic semiconductors and to optimize the level performance of their corresponding devices. Nonetheless, the exact doping mechanism that...

The integration of triplet–triplet annihilation (TTA) components as electrically and optically active elements in vertically-configured photoactive device architectures is a challenging task to achieve. Herein we present a simple methodology for incorporating a photon absorbing layer of the (2,3,7,8,12,13,17,18-octaethyl-porphyrinato)platinum(II) (...

Disentangling temporally-overlapping charge carrier recombination events in organic bulk heterojunctions by optical spectroscopy is challenging. Here, a new methodology for employing delayed luminescence spectroscopy is presented. The proposed method is capable of distinguishing between recombination of spatially-separated charge carriers and trap-...

Gaining deep insight on the operative mechanism of organic photovoltaic (OPV) devices made of perylene-diimide (PDI) electron acceptors is challenging. Herein we perform a comparative study of three different solution-processable...

The use of photon energy up-converted luminescence driven by triplet-exciton annihilation reactions (TTA-UC) is increasingly gaining attention for developing next-generation light-management, and wavelength-shifting technologies. Here we present a spectroscopic study...

The formation of different types of structural polymorphs of poly(3-hexyl-thiophene) (P3HT) affects the performance of organic photovoltaic (OPV) devices that use thermally-annealed P3HT:PCBM[60] blend films as photoactive layer. Here it is demonstrated that, when densely-packed and non-densely packed P3HT polymorphs co-exist in the P3HT:PCBM[60] l...

Elucidating the role of atomic degrees of freedom in organic blends and hybrid perovskites is crucial to understanding the non-adiabatic dynamics within their energy landscape and to their implementation in photovoltaics technologies. Here, we report the direct visualization of the long-range lattice dynamics in rr-P3HT:PC71BM and CH3NH3PbI3 upon f...

Hitherto, great strides have been made in the development of organic systems that exhibit triplet-triplet annihilation induced photon-energy up-conversion (TTA-UC). Yet, the exact role of intermolecular states in solid-state TTA-UC composites remains elusive. Here we perform a comprehensive spectroscopic study in a series of solution processable so...

Herein we present the design of three perylene diimide (PDI) derivatives with different molecular geometry; namely the monomeric PDI1, the bay-linked PDI2 dimer, and the bay-linked PDI4 tetramer with 9,9’-spirobifluorene core that are utilized as electron acceptors in non-fullerene organic solar cells (OSCs). In all cases the PTB7-Th polymer is use...

Optoelectronic properties, supramolecular assemblies, and morphology variation of polymeric semiconductors are governed by six fundamental chemical features. These features are molecular weight, bond length alternation (BLA), planarity, aromatic resonance energy, substituents, and intermolecular interactions. Of these features the specific role of...

The control on the charge transport properties of ternary organic photovoltaic P3HT:PCBM:QBT devices is enabled by modulating the distribution of P3HT polymorphs in the device photoactive layers. Negligible amounts of QBT induce striking modifications in the P3HT lamellar stacking direction, forming both densely packed and non-densely packed P3HT c...

Three kinds of charged star‐shaped conjugated macroelectrolytes, named as PhNBr, TPANBr, and TrNBr, are synthesized as electron‐collecting interlayers for inverted polymer solar cells (i‐PSCs). Based on these well‐defined structured interlayer materials, the light soaking (LS) effect observed in i‐PSCs was studied systematically and accurately. The...

Supplementary

Perylene diimide (PDI)-based organic photovoltaic devices can potentially deliver high power conversion efficiency values provided the photon energy absorbed is utilized efficiently in charge transfer (CT) reactions instead of being consumed in non-radiative energy transfer (ET) steps. Hitherto, it remains unclear whether ET or CT primarily drives...

Cyclopentadithiophene and benzothiadiazole based donor-acceptor polymers are fast emerging as the most promising class of materials for organic solar cells. Here we report on a series of cyclopentadithiophene and benzothiadiazole based conjugated polymers, poly(4,7-bis-(4,4-dioctyl-4H-cyclopenta[2,1-b;3,4-b’]dithiophene-2-yl)-benzo[1,2,5]thiadiazol...

Unlabelled: The performance of organic photovoltaic devices (OPV) with nanostructured polymer:perylene diimide (PDI) photoactive layers approaches the levels of the corresponding polymer:fullerene systems. Nevertheless, a coherent understanding of the difficulty for PDI-based OPV devices to deliver high power conversion efficiencies remains elusiv...

The influence of the monomer’s isomeric structures on the optical, electrochemical, charge transporting properties and photovoltaic performance of donor-acceptor (D-A) conjugated polymers is demonstrated for the first time by studying two D-A copolymers consisting of the bis(3-octyloxy)phenyl)quinoxaline as the electron deficient unit and the two i...

A star-shaped monodisperse conjugated macroelectrolyte grafted with cationic side chains, TrNBr, was designed, synthesized, and utilized as efficient electron-collecting cathode interlayers for inverted polymer solar cells. A neutral one composed of identical star-shaped conjugated backbone, TrOH, was also investigated for comparison. The surface p...

We present a depth-resolved X-ray photoemission spectroscopy study of the Poly(9,9’-dioctylfluorene-cobenzothiadiazole): Perylene tetracarboxylic diimide blend (briefly, F8BT:PDI), employed for the realization of the light harvesting layer in organic photovoltaic devices. We address the problem of the vertical distribution of PDI molecules in the...

The aggregate-induced limitation for high power-conversion efficiencies (PCEs) of perylene-diimide (PDI):polymer solar cells can be circumvented when two simple rules are respected; the aggregate size of PDI remains short enough and the omnipresent PDI aggregates are well electronically-interconnected. Following these guidelines, a PCE of 3.7% is d...

Hitherto, the role of the enhanced intermolecular interactions and the effect of lowering the temperature on the process of triplet–triplet annihilation-induced up-converted delayed luminescence in solid-state composites systems have remained controversial. Here we address these issues by performing temperature-dependent time-integrated and time-ga...

Here we present a temperature dependent spectroscopic study of a solution-processed solid state photon up-converting composite. In our work we address the process of low-energy photon up-conversion at low temperatures in the previously studied blend film of the triplet photosensitizer (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) platinum(II)) (PtOE...

Herein we present a methodology for improving the power conversion efficiency of organic solar cells made by photoactive layers of poly(3-hexylthiophene) (P3HT) and phenyl-C61 butyric acid methyl ester (PCBM) of non-optimized microstructure. In our study we achieve a 47% improvement in the power conversion efficiency (PCE) of the device by utilizin...

We describe the use of a modified Stern–Volmer photokinetic model for the determination of the oxygen-permeation coefficient (PO2) of materials that can be used as barriers against oxygen permeation in organic electronic applications. The model is applied on photophysical data collected based on the use of the optical technique of phosphorimetry fo...

Charge transport dynamics in solar cell devices based on as-spun and annealed P3HT:PCBM films are compared using ultrafast time-resolved optical probing of the electric field by means of field-induced second harmonic generation. The results show that charge carriers drift about twice as far during the first 3 ns after photogeneration in a device wh...

The exceptional interest in improving the limitations of data storage, molecular electronics and optoelectronics has promoted the development of an ever increasing number of techniques used to pattern polymers at micro and nanoscale. Most of them rely on atomic force microscopy to thermally or electrostatically induce mass transport, thereby creati...

Herein we present a detailed study of the structure-function relationship in the organic photovoltaic (OPV) blend film composed of N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and the low energy gap copolymer of poly[4,8-bis-substituted-benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b]thiophene-2,...

Herein we demonstrate a method to improve the power conversion efficiency (PCE) parameter of organic photovoltaic (OPV) devices based on the electron acceptor N,N’-bis(1- ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (PDI) blended with the electron donor poly(indenofluorene)-aryloctyl (PIF-Aryl). The device parameters of the short-circuit...

Solar cells based on conjugated polymer and fullerene blends have been developed as a low-cost alternative to silicon. For efficient solar cells, electron-hole pairs must separate into free mobile charges that can be extracted in high yield. We still lack good understanding of how, why and when carriers separate against the Coulomb attraction. Here...

Here we present ultrafast transient absorption spectroscopy and cw-photoinduced absorption spectroscopy as useful tools for monitoring and investigating the photo-generated charges in organic molecule-based photovoltaics.

We investigate the relationship between processing parameters and the device performance of gravure printed organic solar cells. Ink viscosity, surface energy and surface roughness are studied to optimise the printing process. Surfactants, additives and surface modification by plasma cleaning are utilised to achieve homogeneous printing of multilay...

Evidence for a correlation between the dynamics of emissive non-geminate charge recombination within organic photovoltaic (OPV) blend films and the photocurrent generation efficiency of the corresponding blend-based solar cells is presented. Two model OPV systems that consist of binary blends of electron acceptor N′-bis(1-ethylpropyl)-3,4,9,10-pery...

Charge generation and recombination are studied in blend films of poly-3-hexylthiophene (P3HT) and [6,6']phenyl C61 butyric acid methyl ester (PCBM) using ultrafast transient absorption spectroscopy. We find that the charge generation yield depends upon both blend film composition and thermal annealing. The data suggest that recombination occurs ov...

The mechanism of triplet–triplet annihilation (TTA)-induced up-converted (UC) delayed luminescence is studied in two different binary organic systems consisting of platinum(II) octaethyl porphyrin (PtOEP) mixed with either poly(fluorene) (PF26) or ladder-type pentaphenylene (L5Ph). Cyclic voltammetry and differential pulse voltammetry are employed...

Herein, we address the reduction in the external quantum efficiency (EQE) of solution-processed organic photodetectors caused by the room temperature phase demixing of components in the composite material of the photoactive layer. The reduction takes place under ambient conditions and after the completion of device fabrication. As a model system, w...

Inverted organic photovoltaic devices have been fabricated by gravure printing on a flexible substrate. In order to enable printing of multiple layers sequentially, a systematic study of wetting behaviour of each layer in the device is performed. Successful wetting of a hydrophobic P3HT:PCBM surface by a hydrophilic PEDOT:PSS ink is achieved with t...

The effect of replacing [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) by its multiadduct analogs (bis-PCBM and tris-PCBM) in bulk heterojunction organic solar cells with poly(3-hexylthiophene-2,5-diyl) (P3HT) is studied in terms of blend film microstructure, photophysics, electron transport properties, and device performance. Although the power...

Organic photovoltaics: Following the direct photoexcitation of the low-energy optical gap PDI component in the F8BT:PDI photovoltaic blend film (step 1), charge generation takes place (steps 2, 3). Non-geminate charge recombination (step 4) results in the generation of delayed luminescence (DL) in the mu s time scale (step 5). The DL spectrum origi...

Organic photodiodes are presented that utilize solution-processed perylene diimide bulk heterojunctions as the device photoactive layer. The polymer (9,9′-dioctylfluorene-co-benzothiadiazole; F8BT) is used as the electron donor and the N,N′-bis(1-ethylpropyl)-3,4,9,10-perylene tetracarboxylic diimide (PDI) derivative is used as the electron accepto...

Herein we address the factors controlling photocurrent generation in P3HT:PCBM blend films as a function of blend composition and annealing treatment. Absorption, photoluminescence, and transient absorption spectroscopy are used to distinguish the role of exciton dissociation, charge pair separation, and charge collection. Variations in blend film...

We study charge generation and recombination in organic solar cells that utilize perylene tetracarboxydiimide (PDI) as in electron acceptor and a conjugated polymer as all electron donor. PDI is a promising electron acceptor because of its strong red absorption, LUMO well placed to accept electrons from many conjugated polymers, and good electron m...

We present results of steady-state and transient photoluminescence studies of molecularly doped poly(fluorene) films. We study blends with increasing content of the triplet emitter (2,3,7,8,12,13,17,18-octaethyl-porphyrinato)Pt(II) (PtOEP) when dispersed in the polymeric poly(fluorene) matrix of the poly[9,9-di-(2-ethylhexyl)-fluorenyl-2,7-diyl] (P...

We have investigated the effects of thickness variation and thermal treatment of the electrode polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) in photovoltaic and photodetector devices using conjugated polymer blends as the photoactive material. By variation of the PEDOT:PSS layer thickness between 25 and 150 nm, we...

We present photodiodes fabricated with several layers of semiconducting polymers, designed to show low dark current under reverse bias operation. Dark current minimization is achieved through the presence of additional polymer layers that reduce charge carrier injection in reverse bias, when in contact with the device electrodes. All polymer layers...

Photovoltaic devices incorporating perylene-substituted polyisocyanide materials have been demonstrated, using blend systems with polythiophene- and polyfluorene-based conjugated polymers. Prototypical structures with nominal (1:1) blend weight ratios of the polyisocyanide with poly(3-hexylthiophene) (P3HT) and poly(9,9′-dioctylfluorene-co-bis(N,N′...

We report time-resolved photoluminescence (PL) spectroscopy study of solutions and thin films of pure penta-fluorenes with varying alkyl side-chain structures. While no low-energy green emissions were observed in solutions, spin-cast and vacuum dried initial films exhibited low-energy emission in time-delayed PL spectra, centered at 490nm, whose in...

In the present work, we correlate the photophysical and photovoltaic properties with the respective film morphologies of three different blends made of the fluorene copolymers poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT), poly[9,9′-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine] (TFB), and poly[9,9′-dioctyfluorene-co-bis-N,N′-(4-butylph...

The x-ray stability of photodiodes made of poly(9,9-di-n-octylfluorene-co-benzothiadiazole):perylene diimide, poly[2,7-(9,9-di-n-octylfluorene)-co-(1,4-phenylene-[(4-sec-butylphenyl)imino]-1,4-phenylene)]:perylene diimide and poly(3-hexylthiophene):([6,6]-phenylC61-butyric acid methyl ester) (P3HT:PCBM) blends has been examined up to lifetime doses...

We investigate the potential for replacing inorganic semiconductors with polymeric semiconductors in medical X-ray imaging applications. Polymeric semiconductors are soft and can be fabricated using techniques such as spin coating and jet printing, leading to reductions in fabrication costs for large-area arrays, easy integration of heterostructure...

Spectroscopic and morphological studies on a series of rod-coil block copolymers containing terfluorene segments as the rigid blocks and polystyrene as the flexible parts demonstrate an increase in the photoluminescence intensity and the exciton lifetime as well as formation of isolated spheres as thin films upon thermal annealing in air (200 degre...

We report on amplification of blue light (469 nm) via amplified spontaneous emission in asymmetric planar waveguides of a fully arylated polyindenofluorene derivative. A very low threshold value of about 3 μJ/cm2 ( ∼ 375 W/cm2) for amplification of light has been demonstrated by pumping the waveguides at 3.0 eV (410 nm) with a stripe shape excitati...

Time-resolved photoluminescence spectroscopy experiments of three poly(2,8-indenofluorene) derivatives bearing different pendant groups are presented. A comparison of the photophysical properties of dilute solutions and thin films provides information on the chemical purity of the materials. The photophysical properties of poly(2,8-indenofluorene)s...

Up-conversion photoluminescence in a blue-emitting polymer doped with porphyrin macrocycles has been investigated and the component distribution of this system has been optimised. Covalent binding of the porphyrins to the polymer was implemented to decrease the separation of the dopant and matrix molecules, as well as dopant aggregation. The result...

We report on the optimization of the upconversion photoluminescence in films of conjugated polymers doped with platinum porphyrin. The upconversion emission was observed to take place at pump intensities as low as 0.5 kW / cm ² . Comparison between the photoluminescence integral intensity of polyfluorene and ladder-type pentaphenylene po...

The up-conversion photoluminescence (PL) in films of polyfluorene (PF) doped with metallated porphyrins is reported for the first time. The dependence of the up-conversion process on the pump laser intensity and wavelength, the central metal moiety of the dopants, and the temperature is presented. Up-conversion emission is observed at pump intensit...

TiO2-based nanostructured Fe3+-doped coatings have been prepared by the sol–gel method on glass substrates. The coatings were characterized by X-ray diffraction and spectroellipsometry methods. The influence of Fe3+ dopant concentration, number of coatings, and calcination temperature on the films structure was established. The antibacterial activi...

Dendronization has previously been suggested as a means of controlling the level of intermolecular interactions in macromolecular and polymeric compounds. We therefore studied the spectral relaxation dynamics of dendronized and non-dendronized polyfluorenes at different temperatures. Dendronization strongly affects inhomogeneous spectral broadening...