Materials

Research

Jump to: Review

11 pages, 2675 KiB

Open AccessArticle

Single-Component Organic Solar Cells Based on Intramolecular Charge Transfer Photoabsorption

by Ken-ichi Nakayama, Tatsuya Okura, Yuki Okuda, Jun Matsui, Akito Masuhara, Tsukasa Yoshida, Matthew Schuette White, Cigdem Yumusak, Phillip Stadler, Markus Scharber and Niyazi Serdar Sariciftci

Materials 2021, 14(5), 1200; https://doi.org/10.3390/ma14051200 - 04 Mar 2021

Cited by 12 | Viewed by 2959

Abstract

Conjugated donor–acceptor molecules with intramolecular charge transfer absorption are employed for single-component organic solar cells. Among the five types of donor–acceptor molecules, the strong push–pull structure of DTDCPB resulted in solar cells with high J_SC, an internal quantum efficiency exceeding 20%, [...] Read more.

Conjugated donor–acceptor molecules with intramolecular charge transfer absorption are employed for single-component organic solar cells. Among the five types of donor–acceptor molecules, the strong push–pull structure of DTDCPB resulted in solar cells with high J_SC, an internal quantum efficiency exceeding 20%, and high V_OC exceeding 1 V with little photon energy loss around 0.7 eV. The exciton binding energy (EBE), which is a key factor in enhancing the photocurrent in the single-component device, was determined by quantum chemical calculation. The relationship between the photoexcited state and the device performance suggests that the strong internal charge transfer is effective for reducing the EBE. Furthermore, molecular packing in the film is shown to influence photogeneration in the film bulk. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

12 pages, 1864 KiB

Open AccessArticle

Interface Tuning between Two Connecting Bulk Heterojunctions in Small Molecule Bilayer Ternary Solar Cells

by Qi Jiang and Yingjie Xing

Materials 2020, 13(21), 4833; https://doi.org/10.3390/ma13214833 - 29 Oct 2020

Cited by 1 | Viewed by 1645

Abstract

Bilayer ternary solar cells are a kind of novel organic photovoltaic device with a triple-component active layer but are different from the ternary bulk heterojunction (BHJ) blend. Two binary BHJs with a common acceptor (or donor) are deposited sequentially in this kind of [...] Read more.

Bilayer ternary solar cells are a kind of novel organic photovoltaic device with a triple-component active layer but are different from the ternary bulk heterojunction (BHJ) blend. Two binary BHJs with a common acceptor (or donor) are deposited sequentially in this kind of device. Here, we study the fabrication and optimization of bilayer ternary solar cells using metal phthalocyanine donors and fullerene acceptor. The device power conversion efficiency (PCE) shows a significant dependence on the interface between the two binary BHJs. The interface formed by stacking two BHJs directly demonstrates severe restrictions on the device efficiency. We find that the photovoltaic performance of bilayer ternary cells can be improved by inserting a C60 molecular monolayer between the two binary BHJs. The effect of the C60 interfacial layer on charge transport is analyzed based on their transport characteristics under negative bias. A relationship between the C60 interfacial layer and recombination under illumination is discussed. This work reveals a particular influence due to the interface facing three materials in organic solar cells. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

15 pages, 1980 KiB

Open AccessArticle

Revisiting the Charge-Transfer States at Pentacene/C₆₀ Interfaces with the GW/Bethe–Salpeter Equation Approach

by Takatoshi Fujita, Yoshifumi Noguchi and Takeo Hoshi

Materials 2020, 13(12), 2728; https://doi.org/10.3390/ma13122728 - 16 Jun 2020

Cited by 2 | Viewed by 1978

Abstract

Molecular orientations and interfacial morphologies have critical effects on the electronic states of donor/acceptor interfaces and thus on the performance of organic photovoltaic devices. In this study, we explore the energy levels and charge-transfer states at the organic donor/acceptor interfaces on the basis [...] Read more.

Molecular orientations and interfacial morphologies have critical effects on the electronic states of donor/acceptor interfaces and thus on the performance of organic photovoltaic devices. In this study, we explore the energy levels and charge-transfer states at the organic donor/acceptor interfaces on the basis of the fragment-based GW and Bethe–Salpeter equation approach. The face-on and edge-on orientations of pentacene/C₆₀ bilayer heterojunctions have employed as model systems. GW+Bethe–Salpeter equation calculations were performed for the local interface structures in the face-on and edge-on bilayer heterojunctions, which contain approximately 2000 atoms. Calculated energy levels and charge-transfer state absorption spectra are in reasonable agreements with those obtained from experimental measurements. We found that the dependence of the energy levels on interfacial morphology is predominantly determined by the electrostatic contribution of polarization energy, while the effects of induction contribution in the edge-on interface are similar to those in the face-on. Moreover, the delocalized charge-transfer states contribute to the main absorption peak in the edge-on interface, while the face-on interface features relatively localized charge-transfer states in the main absorption peak. The impact of the interfacial morphologies on the polarization and charge delocalization effects is analyzed in detail. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Graphical abstract

15 pages, 3107 KiB

Open AccessArticle

Modulated Photocurrent Spectroscopy Study of the Electronic Transport Properties of Working Organic Photovoltaics: Degradation Analysis

by Emi Nakatsuka, Yo Kumoda, Kiyohito Mori, Takashi Kobayashi, Takashi Nagase and Hiroyoshi Naito

Materials 2020, 13(11), 2660; https://doi.org/10.3390/ma13112660 - 11 Jun 2020

Cited by 2 | Viewed by 2539

Abstract

Electronic transport measurement using modulated photocurrent (MPC) spectroscopy is demonstrated herein in working organic photovoltaics (OPVs) before and after AM1.5G irradiation. OPVs with bulk heterojunction (BHJ) using prototypical donor and acceptor materials, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1–2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] = hieno [3–4-b]thiophenediyl]] (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC [...] Read more.

Electronic transport measurement using modulated photocurrent (MPC) spectroscopy is demonstrated herein in working organic photovoltaics (OPVs) before and after AM1.5G irradiation. OPVs with bulk heterojunction (BHJ) using prototypical donor and acceptor materials, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1–2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] = hieno [3–4-b]thiophenediyl]] (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁BM), were fabricated. The OPVs had inverted structures (BHJs are formed on transparent conductive oxide substrates). The photovoltaic performance of PTB7:PC₇₁BM OPVs was characterized and the best power conversion efficiency was obtained at PTB7 content of 40 wt%. Electron and hole mobility were determined with MPC spectroscopy in PTB7:PC₇₁BM OPVs and were well balanced at PTB7 content of 40 wt%. Degradation of the photovoltaic performance of PTB7:PC₇₁BM OPVs with PTB7 content of 40 wt% caused by AM1.5G irradiation was studied. MPC spectroscopy showed that the well-balanced mobility was not affected by AM1.5G irradiation. The degradation of OPVs was not due to changes in the electronic transport properties, but mainly to the reduced short circuit current (J_sc) and fill factor (FF). The origin of this reduction is discussed. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

16 pages, 2881 KiB

Open AccessArticle

A Windmill-Shaped Molecule with Anthryl Blades to Form Smooth Hole-Transport Layers via a Photoprecursor Approach

by Akihiro Maeda, Aki Nakauchi, Yusuke Shimizu, Kengo Terai, Shuhei Sugii, Hironobu Hayashi, Naoki Aratani, Mitsuharu Suzuki and Hiroko Yamada

Materials 2020, 13(10), 2316; https://doi.org/10.3390/ma13102316 - 18 May 2020

Cited by 1 | Viewed by 2504

Abstract

Preparation of high-performance organic semiconductor devices requires precise control over the active-layer structure. To this end, we are working on the controlled deposition of small-molecule semiconductors through a photoprecursor approach wherein a soluble precursor compound is processed into a thin-film form and then [...] Read more.

Preparation of high-performance organic semiconductor devices requires precise control over the active-layer structure. To this end, we are working on the controlled deposition of small-molecule semiconductors through a photoprecursor approach wherein a soluble precursor compound is processed into a thin-film form and then converted to a target semiconductor by light irradiation. This approach can be applied to layer-by-layer solution deposition, enabling the preparation of p–i–n-type photovoltaic active layers by wet processing. However, molecular design principles are yet to be established toward obtaining desirable thin-film morphology via this unconventional method. Herein, we evaluate a new windmill-shaped molecule with anthryl blades, 1,3,5-tris(5-(anthracen-2-yl)thiophen-2-yl)benzene, which is designed to deposit via the photoprecursor approach for use as the p-sublayer in p–i–n-type organic photovoltaic devices (OPVs). The new compound is superior to the corresponding precedent p-sublayer materials in terms of forming smooth and homogeneous films, thereby leading to improved performance of p–i–n OPVs. Overall, this work demonstrates the effectiveness of the windmill-type architecture in preparing high-quality semiconducting thin films through the photoprecursor approach. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

8 pages, 2686 KiB

Open AccessArticle

Donor/Acceptor Photovoltaic Cells Fabricated on p-Doped Organic Single-Crystal Substrates

by Yusuke Yabara, Seiichiro Izawa and Masahiro Hiramoto

Materials 2020, 13(9), 2068; https://doi.org/10.3390/ma13092068 - 30 Apr 2020

Cited by 2 | Viewed by 2115

Abstract

In this study, the operation of donor/acceptor photovoltaic cells fabricated on homoepitaxially grown p-doped rubrene single-crystal substrates is demonstrated. The photocurrent density is dominated by the sheet conductivity (σ_□) of the p-type single-crystal layer doped to 100 ppm with [...] Read more.

In this study, the operation of donor/acceptor photovoltaic cells fabricated on homoepitaxially grown p-doped rubrene single-crystal substrates is demonstrated. The photocurrent density is dominated by the sheet conductivity (σ_□) of the p-type single-crystal layer doped to 100 ppm with an iron chloride (Fe₂Cl₆) acceptor. A 65 μm thick p-type rubrene single-crystal substrate is expected to be required for a photocurrent density of 20 mA·cm⁻². An entire bulk doping technique for rubrene single crystals is indispensable for the fabrication of practical organic single-crystal solar cells. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

11 pages, 1627 KiB

Open AccessArticle

Electronic and Crystallographic Examinations of the Homoepitaxially Grown Rubrene Single Crystals

by Yasuo Nakayama, Masaki Iwashita, Mitsuru Kikuchi, Ryohei Tsuruta, Koki Yoshida, Yuki Gunjo, Yusuke Yabara, Takuya Hosokai, Tomoyuki Koganezawa, Seiichiro Izawa and Masahiro Hiramoto

Materials 2020, 13(8), 1978; https://doi.org/10.3390/ma13081978 - 23 Apr 2020

Cited by 9 | Viewed by 3218

Abstract

Homoepitaxial growth of organic semiconductor single crystals is a promising methodology toward the establishment of doping technology for organic opto-electronic applications. In this study, both electronic and crystallographic properties of homoepitaxially grown single crystals of rubrene were accurately examined. Undistorted lattice structures of [...] Read more.

Homoepitaxial growth of organic semiconductor single crystals is a promising methodology toward the establishment of doping technology for organic opto-electronic applications. In this study, both electronic and crystallographic properties of homoepitaxially grown single crystals of rubrene were accurately examined. Undistorted lattice structures of homoepitaxial rubrene were confirmed by high-resolution analyses of grazing-incidence X-ray diffraction (GIXD) using synchrotron radiation. Upon bulk doping of acceptor molecules into the homoepitaxial single crystals of rubrene, highly sensitive photoelectron yield spectroscopy (PYS) measurements unveiled a transition of the electronic states, from induction of hole states at the valence band maximum at an adequate doping ratio (10 ppm), to disturbance of the valence band itself for excessive ratios (≥ 1000 ppm), probably due to the lattice distortion. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

8 pages, 1416 KiB

Open AccessArticle

Photoconversion Mechanism at the pn-Homojunction Interface in Single Organic Semiconductor

by Ji-Hyun Lee, Armand Perrot, Masahiro Hiramoto and Seiichiro Izawa

Materials 2020, 13(7), 1727; https://doi.org/10.3390/ma13071727 - 07 Apr 2020

Cited by 2 | Viewed by 3198

Abstract

Clarifying critical differences in free charge generation and recombination processes between inorganic and organic semiconductors is important for developing efficient organic photoconversion devices such as solar cells (SCs) and photodetector. In this study, we analyzed the dependence of doping concentration on the photoconversion [...] Read more.

Clarifying critical differences in free charge generation and recombination processes between inorganic and organic semiconductors is important for developing efficient organic photoconversion devices such as solar cells (SCs) and photodetector. In this study, we analyzed the dependence of doping concentration on the photoconversion process at the organic pn-homojunction interface in a single organic semiconductor using the temperature dependence of J–V characteristics and energy structure measurements. Even though the organic pn-homojunction SC devices were fabricated using a single host material and the doping technique resembling an inorganic pn-homojunction, the charge generation and recombination mechanisms are similar to that of conventional donor/acceptor (D/A) type organic SCs; that is, the charge separation happens from localized exciton and charge transfer (CT) state being separated by the energy offset between adjacent molecules, and the recombination happens from localized charge carrier at two adjacent molecules. The determining factor for photoconversion processes is the localized nature of charges in organic semiconductors. The results demonstrated that controlling the delocalization of the charges is important to realize efficient organic photoconversion devices. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

Review

Jump to: Research

12 pages, 2382 KiB

Open AccessReview

Distributions of Potential and Contact-Induced Charges in Conventional Organic Photovoltaics

by Kouki Akaike

Materials 2020, 13(10), 2411; https://doi.org/10.3390/ma13102411 - 24 May 2020

Cited by 4 | Viewed by 2666

Abstract

The interfaces of dissimilar materials play central roles in photophysical events in organic photovoltaics (OPVs). Depth profiles of electrostatic potential and contact-induced charges determine the energy-level lineup of the frontier orbitals at electrode/organic and organic heterointerfaces. They are critical for the elementary processes [...] Read more.

The interfaces of dissimilar materials play central roles in photophysical events in organic photovoltaics (OPVs). Depth profiles of electrostatic potential and contact-induced charges determine the energy-level lineup of the frontier orbitals at electrode/organic and organic heterointerfaces. They are critical for the elementary processes in an OPV cell, such as generation and diffusion of free carriers. A simple electrostatic model describes the energetics in organic heterojunctions supported by an electrode, and experiments via photoelectron spectroscopy and the Kelvin probe method validate the potential distribution in the stacking direction of the device. A comparative study has clarified the significance of Fermi-level pinning and resulting electrostatic fields in determining the energy-level alignment. In this review, we discuss how parameters of device constituents affect the distributions of potential and the dark charges in conventional OPVs comprising metallophthalocyanine and C₆₀ as donor and acceptor, respectively. The results of previous studies, together with additional numerical simulations, suggest that a number of the factors influence the depth profiles of the dark charge and potential, such as the work function of bottom materials, layer thickness, structural inhomogeneity at interfaces, top electrode, and stacking sequence. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

19 pages, 3181 KiB

Open AccessReview

Metal Oxide Compact Electron Transport Layer Modification for Efficient and Stable Perovskite Solar Cells

by Md. Shahiduzzaman, Shoko Fukaya, Ersan Y. Muslih, Liangle Wang, Masahiro Nakano, Md. Akhtaruzzaman, Makoto Karakawa, Kohshin Takahashi, Jean-Michel Nunzi and Tetsuya Taima

Materials 2020, 13(9), 2207; https://doi.org/10.3390/ma13092207 - 11 May 2020

Cited by 42 | Viewed by 7964

Abstract

Perovskite solar cells (PSCs) have appeared as a promising design for next-generation thin-film photovoltaics because of their cost-efficient fabrication processes and excellent optoelectronic properties. However, PSCs containing a metal oxide compact layer (CL) suffer from poor long-term stability and performance. The quality of [...] Read more.

Perovskite solar cells (PSCs) have appeared as a promising design for next-generation thin-film photovoltaics because of their cost-efficient fabrication processes and excellent optoelectronic properties. However, PSCs containing a metal oxide compact layer (CL) suffer from poor long-term stability and performance. The quality of the underlying substrate strongly influences the growth of the perovskite layer. In turn, the perovskite film quality directly affects the efficiency and stability of the resultant PSCs. Thus, substrate modification with metal oxide CLs to produce highly efficient and stable PSCs has drawn attention. In this review, metal oxide-based electron transport layers (ETLs) used in PSCs and their systemic modification are reviewed. The roles of ETLs in the design and fabrication of efficient and stable PSCs are also discussed. This review will guide the further development of perovskite films with larger grains, higher crystallinity, and more homogeneous morphology, which correlate to higher stable PSC performance. The challenges and future research directions for PSCs containing compact ETLs are also described with the goal of improving their sustainability to reach new heights of clean energy production. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

31 pages, 4392 KiB

Open AccessReview

Development of Perylene-Based Non-Fullerene Acceptors through Bay-Functionalization Strategy

by Keisuke Fujimoto, Masaki Takahashi, Seiichiro Izawa and Masahiro Hiramoto

Materials 2020, 13(9), 2148; https://doi.org/10.3390/ma13092148 - 06 May 2020

Cited by 25 | Viewed by 5232

Abstract

Perylene has had a tremendous impact in the history of material research for the molecular semiconductors. Among numerous derivatives of this polyaromatic hydrocarbon, perylene diimide (PDI) represents a promising class of organic materials envisioned as non-fullerene acceptors (NFAs) for the practical organic photovoltaic [...] Read more.

Perylene has had a tremendous impact in the history of material research for the molecular semiconductors. Among numerous derivatives of this polyaromatic hydrocarbon, perylene diimide (PDI) represents a promising class of organic materials envisioned as non-fullerene acceptors (NFAs) for the practical organic photovoltaic (OPV) applications due to their enhanced photo- and thermal stability and remarkably high electron affinity, some of which realize band-like transport properties. The present review guides some of the representative achievements in the development of rationally designed PDI systems, highlighting synthetic methodologies based on bay-functionalization strategies for creating well-designed molecular nanostructures and structure-performance relationship of perylene-based small molecular acceptors (SMAs) for the photovoltaic outcomes. Full article

(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Organic Solar Cell and Optoelectronic Functional Materials

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (11 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI