Special Issue "Organic Photovoltaics"

A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (31 October 2015).

Special Issue Editors

Dr. Laure Biniek
E-Mail Website
Guest Editor
Institut Charles Sadron, CNRS-Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg, France
Tel. +33 (0)388 41 41 78
Interests: pi-conjugated materials chemistry, opto-electronic properties, structure and morphology of semi-conducting polymers, transmission electron microscopy, organic photovoltaics
Special Issues and Collections in MDPI journals
Dr. Christian B. Nielsen
E-Mail Website
Guest Editor
Materials Research Institute and School of Biological and Chemical Sciences, Queen Mary University of London, United Kingdom
Tel. +44 (0)20 7882 5902
Interests: materials chemistry; Conjugated polymers; Organic electronics; Organic bioelectronics; Organic photovoltaics; Field-effect transistors
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

With this Special Issue on organic photovoltaics, we hope to bring an inspiring view on current trends and research focuses within the exciting and rapidly evolving field of polymer-based organic photovoltaics.

In response to other competing technologies, organic photovoltaics have progressed significantly over recent years, with both small molecule and polymeric electron donors now affording power conversion efficiencies above 10% in single junction devices with fullerene electron acceptors. While fullerene based acceptors are still dominating the research landscape, much research has recently been devoted to the development of alternative non-fullerene acceptors. This area is currently undergoing a prolific development with numerous small molecule and polymeric acceptor materials emerging as promising candidates that provide alternatives to PCBM and which further advance the field of organic photovoltaics.

The efficiency boost promised by multi-junction devices has sparked a renewed interest in efficient wide band gap donor materials and in extremely narrow band gap materials, so as to cover as much of the solar spectrum as possible. Recent years have also seen a stronger focus on solar cell device morphology and stability; it is becoming clear that understanding and controlling blend morphology is crucial for improving photovoltaic device stability.

Although much progress has been made in the field, major challenges still have to be overcome in order to drive this technology forward towards the realization of efficient, cheap, and flexible organic solar cells that are compatible with environmentally friendly, high throughput printing technologies. This Special Issue of Polymers will address some of these remaining challenges, with a focus on polymeric photoactive materials and their structure-property relationships in the context of solar cell performance, blend morphology control, and operational stability.

Dr. Christian B. Nielsen
Dr. Laure Biniek
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Organic photovoltaics
  • Polymeric photoactive materials
  • New synthetic methodologies toward photoactive materials
  • Environmentally friendly synthesis of photoactive materials
  • Non-fullerene acceptors
  • Polymer-polymer solar cells
  • Organic photovoltaic device stability
  • Bulk heterojunction blend morphology
  • Multi-junction organic solar cells
  • Large scale device processing
  • Environmentally friendly device processing

Related Special Issue

Published Papers (7 papers)

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Editorial

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Open AccessEditorial
Organic Photovoltaics: More than Ever, an Interdisciplinary Field
Polymers 2016, 8(3), 70; https://doi.org/10.3390/polym8030070 - 02 Mar 2016
Cited by 1
Abstract
Despite the growing interest and rapid advancement of alternative photovoltaic (PV) technologies such as perovskite based PV devices, we still believe that organic photovoltaic (OPV) devices have a significant potential for stable, low-cost solar power generation. [...] Full article
(This article belongs to the Special Issue Organic Photovoltaics)

Research

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Open AccessFeature PaperArticle
Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells
Polymers 2016, 8(1), 14; https://doi.org/10.3390/polym8010014 - 13 Jan 2016
Cited by 47
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Organic Photovoltaics)
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Open AccessFeature PaperArticle
Energetic Tuning in Spirocyclic Conjugated Polymers
Polymers 2016, 8(1), 9; https://doi.org/10.3390/polym8010009 - 06 Jan 2016
Cited by 4
Abstract
Precise control of the energy levels in a conjugated polymer is the key to allowing their exploitation in optoelectronic devices. The introduction of spirocycles into conjugated polymers has traditionally been used to enhance their solid state microstructure. Here we present a highly novel [...] Read more.
Precise control of the energy levels in a conjugated polymer is the key to allowing their exploitation in optoelectronic devices. The introduction of spirocycles into conjugated polymers has traditionally been used to enhance their solid state microstructure. Here we present a highly novel method of energetic tuning through the use of electronically active spirocyclic systems. By modifying the size and oxidation state of a heteroatom in an orthogonal spirocycle we demonstrate energetic fine tuning in both the absorption and emission of a conjugated polymer. Furthermore, the synthesis of highly novel triplet-decker spirocyclic conjugated polymers is presented. This new method of energetic manipulation in a conjugated polymer paves the way for future application targeted synthesis of polymers with electronically active spirocycles. Full article
(This article belongs to the Special Issue Organic Photovoltaics)
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Open AccessArticle
Comparative Indoor and Outdoor Degradation of Organic Photovoltaic Cells via Inter-laboratory Collaboration
Polymers 2016, 8(1), 1; https://doi.org/10.3390/polym8010001 - 23 Dec 2015
Cited by 10
Abstract
We report on the degradation of organic photovoltaic (OPV) cells in both indoor and outdoor environments. Eight different research groups contributed state of the art OPV cells to be studied at Pomona College. Power conversion efficiency and fill factor were determined from IV [...] Read more.
We report on the degradation of organic photovoltaic (OPV) cells in both indoor and outdoor environments. Eight different research groups contributed state of the art OPV cells to be studied at Pomona College. Power conversion efficiency and fill factor were determined from IV curves collected at regular intervals over six to eight months. Similarly prepared devices were measured indoors, outdoors, and after dark storage. Device architectures are compared. Cells kept indoors performed better than outdoors due to the lack of temperature and humidity extremes. Encapsulated cells performed better due to the minimal oxidation. Some devices showed steady aging but many failed catastrophically due to corrosion of electrodes not active device layers. Degradation of cells kept in dark storage was minimal over periods up to one year. Full article
(This article belongs to the Special Issue Organic Photovoltaics)
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Open AccessArticle
Quantitative Phase Fraction Detection in Organic Photovoltaic Materials through EELS Imaging
Polymers 2015, 7(11), 2446-2460; https://doi.org/10.3390/polym7111523 - 24 Nov 2015
Cited by 8
Abstract
Organic photovoltaic materials have recently seen intense interest from the research community. Improvements in device performance are occurring at an impressive rate; however, visualization of the active layer phase separation still remains a challenge. This paper outlines the application of two electron energy-loss [...] Read more.
Organic photovoltaic materials have recently seen intense interest from the research community. Improvements in device performance are occurring at an impressive rate; however, visualization of the active layer phase separation still remains a challenge. This paper outlines the application of two electron energy-loss spectroscopic (EELS) imaging techniques that can complement and enhance current phase detection techniques. Specifically, the bulk plasmon peak position, often used to produce contrast between phases in energy filtered transmission electron microscopy (EFTEM), is quantitatively mapped across a sample cross section. A complementary spectrum image capturing the carbon and sulfur core loss edges is compared with the plasmon peak map and found to agree quite well, indicating that carbon and sulfur density differences between the two phases also allows phase discrimination. Additionally, an analytical technique for determining absolute atomic areal density is used to produce an absolute carbon and sulfur areal density map. We show how these maps may be re-interpreted as a phase ratio map, giving quantitative information about the purity of the phases within the junction. Full article
(This article belongs to the Special Issue Organic Photovoltaics)
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Open AccessArticle
Roughening Conjugated Polymer Surface for Enhancing the Charge Collection Efficiency of Sequentially Deposited Polymer/Fullerene Photovoltaics
Polymers 2015, 7(8), 1497-1509; https://doi.org/10.3390/polym7081466 - 13 Aug 2015
Cited by 7
Abstract
A method that enables the formation of a rough nano-scale surface for conjugated polymers is developed through the utilization of a polymer chain ordering agent (OA). 1-Chloronaphthalene (1-CN) is used as the OA for the poly(3-hexylthiophene-2,5-diyl) (P3HT) layer. The addition of 1-CN to [...] Read more.
A method that enables the formation of a rough nano-scale surface for conjugated polymers is developed through the utilization of a polymer chain ordering agent (OA). 1-Chloronaphthalene (1-CN) is used as the OA for the poly(3-hexylthiophene-2,5-diyl) (P3HT) layer. The addition of 1-CN to the P3HT solution improves the chain ordering of the P3HT during the film formation process and increases the surface roughness of the P3HT film compared to the film prepared without 1-CN. The roughened surface of the P3HT film is utilized to construct a P3HT/fullerene bilayer organic photovoltaic (OPV) by sequential solution deposition (SqSD) without thermal annealing process. The power conversion efficiency (PCE) of the SqSD-processed OPV utilizing roughened P3HT layer is 25% higher than that utilizing a plain P3HT layer. It is revealed that the roughened surface of the P3HT increases the heterojunction area at the P3HT/fullerene interface and this resulted in improved internal charge collection efficiency, as well as light absorption efficiency. This method proposes a novel way to improve the PCE of the SqSD-processed OPV, which can be applied for OPV utilizing low band gap polymers. In addition, this method allows for the reassessment of polymers, which have shown insufficient performance in the BSD process. Full article
(This article belongs to the Special Issue Organic Photovoltaics)
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Review

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Open AccessFeature PaperReview
Impact of Backbone Fluorination on π-Conjugated Polymers in Organic Photovoltaic Devices: A Review
Polymers 2016, 8(1), 11; https://doi.org/10.3390/polym8010011 - 12 Jan 2016
Cited by 86
Abstract
Solution-processed bulk heterojunction solar cells have experienced a remarkable acceleration in performances in the last two decades, reaching power conversion efficiencies above 10%. This impressive progress is the outcome of a simultaneous development of more advanced device architectures and of optimized semiconducting polymers. [...] Read more.
Solution-processed bulk heterojunction solar cells have experienced a remarkable acceleration in performances in the last two decades, reaching power conversion efficiencies above 10%. This impressive progress is the outcome of a simultaneous development of more advanced device architectures and of optimized semiconducting polymers. Several chemical approaches have been developed to fine-tune the optoelectronics and structural polymer parameters required to reach high efficiencies. Fluorination of the conjugated polymer backbone has appeared recently to be an especially promising approach for the development of efficient semiconducting polymers. As a matter of fact, most currently best-performing semiconducting polymers are using fluorine atoms in their conjugated backbone. In this review, we attempt to give an up-to-date overview of the latest results achieved on fluorinated polymers for solar cells and to highlight general polymer properties’ evolution trends related to the fluorination of their conjugated backbone. Full article
(This article belongs to the Special Issue Organic Photovoltaics)
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