Single-material Organic Solar Cells Research Articles

Enhanced Intramolecular Hole Transfer in Block Copolymer Enables >15% and Operational Stable Single-Material-Organic Solar Cells.

Recent studies on narrow bandgap all-conjugated block copolymer (BCP) single-material-organic solar cells (SMOSCs) have made unprecedented progress in power conversion efficiency (PCE); however, it still lacks understanding of the structure-property relationship in these highly mixed materials. Herein, the impact of different synthetic protocols (direct synthesis (d-BCP) versus sequential synthesis (s-BCP)) is first investigated on the relevant photovoltaic properties. Targeting the same BCP, namely PBDB-T-b-PYIT, it is found that the change in polymerization reaction leads to quite different optical and transport properties. The d-BCP outputs a record-high PCE of 15.02% for SMOSCs as well as enhanced operation stability under simulated 1-sun illumination, which is significantly higher than that of s-BCP (10.33%) and even close to its bulk heterojunction (BHJ) counterparts. Detailed transient absorption spectroscopy reveals ultrafast dynamics of charge transfer (CT) and exciton dissociation in BCP. In together with morphology characterization, it is revealed that the d-BCP has more phase pure composition, enhanced molecular ordering, and higher intramolecular CT efficiency relative to those of s-BCP. These findings gain insight into both the structure and carrier dynamic of BCP and demonstrate the possibility of achieving high-efficiency and stable SMOSCs.

The Application of Y Series Acceptor-Based Double-Cable Polymers in Single-Material Organic Solar Cells

The Application of Y Series Acceptor-Based Double-Cable Polymers in Single-Material Organic Solar Cells

Molecular Donor-Acceptor Dyads for Single-Material Organic Solar Cells.

A series of ambipolar covalently linked oligothiophene-fullerene dyads have been synthesized by systematical structural variations. In this respect, the length of linker between donor and acceptor unit was altered and in a second series the terminal acceptor units in the donor unit of the dyads were varied. Characterization of the optical and redox properties gave valuable structure-property relationships and were correlated to the photovoltaic performance in single-material organic solar cells, in which power conversion efficiencies of up to 4.3 % were reached.

S,N-Heteropentacene-based molecular donor–acceptor dyads: structure–property relationships and application in single-material organic solar cells

Molecular donor–acceptor dyads D11–D18 using S,N-heteropentacenes SN5′ and fullerenic acceptors were synthesized and applied in solution-processed single-material organic solar cells reaching power conversion efficiencies of up to 2.8%.

Stable block copolymer single-material organic solar cells: progress and perspective

The rapidly increasing population and decreasing supply of fossil fuels have resulted in a growing demand for energy, which has brought on an energy crisis.

Structure–properties of small donor–acceptor molecules for homojunction single-material organic solar cells

Small donor–acceptor molecules combining arylamine donor blocks with various acceptors have been synthesized and evaluated as active materials in homojunction single material organic solar cells.

Regioselectivity control of block copolymers for high-performance single-material organic solar cells

Narrow bandgap (NBG) block copolymers are promising materials to realize single-material organic solar cells (SMOSCs) that combine high performance with minimized fabrication procedures.

Molecular Oligothiophene–Fullerene Dyad Reaching Over 5% Efficiency in Single‐Material Organic Solar Cells

A novel donor-acceptor dyad, 4, in which the conjugated oligothiophene donor is covalently connected to fullerene PC71 BM by a flexible alkyl ester linker, is synthesized and applied as photoactive layer in solution-processed single-material organic solar cells (SMOSCs). Excellent photovoltaic performance, including a high short-circuit current density (JSC ) of 13.56mA cm-2 , is achieved, leading to a power conversion efficiency of 5.34% in an inverted cell architecture, which is substantially increased compared to other molecular single materials. Furthermore, dyad 4-based SMOSCs display excellent stability maintaining 96% of the initial performance after 750 h (one month) of continuous illumination and operation under simulated AM 1.5G irradiation. These results will strengthen the rational molecular design to further develop SMOSCs for potential industrial application.

Broadly Applicable Synthesis of Arylated Dithieno[3,2-b:2',3'-d]pyrroles as Building Blocks for Organic Electronic Materials.

A novel and versatile method for the N‐arylation of dithieno[3,2‐b:2′,3′‐d]pyrrole (DTP) is presented. By Pd‐ or Cu‐catalyzed coupling a variety of arenes and acenes were directly attached at the DTP−nitrogen yielding a variety of functionalized DTPs. Investigations on optical and redox properties led to valuable structure‐property relationships, which were corroborated by quantum chemical calculations. Further functionalization and elongation of the conjugation of an acceptor‐substituted DTP was elaborated to result in complex cruciform‐type donor−acceptor oligomers, which were investigated and implemented in single material organic solar cells.

Diffusion-enhanced exciton dissociation in single-material organic solar cells.

Single-material organic solar cells have recently attracted research attention due to their simplicity, morphological robustness and high yield of exciton dissociation. Using α-sexithiophene as a model system, we show that the single-event probability of the exciton dissociation at the boundaries of polycrystalline domains with different molecular orientation is extremely low (∼0.5%), while a high efficiency of charge generation is gained via hundred-fold crossings of the domain boundaries due to the long exciton diffusion length (∼45 nm).

Molecular Donor–Acceptor Dyads for Efficient Single‐Material Organic Solar Cells

Single‐material organic solar cells (SMOSCs) promise several advantages with respect to prospective applications in printed large‐area solar foils. Only one photoactive material has to be processed and the impressive thermal and photochemical long‐term stability of the devices is achieved. Herein, a novel structural design of oligomeric donor–acceptor (D–A) dyads 1–3 is established, in which an oligothiophene donor and fullerene acceptor are covalently linked by a flexible spacer of variable length. Favorable optoelectronic, charge transport, and self‐organization properties of the D–A dyads are the basis for reaching power conversion efficiencies up to 4.26% in SMOSCs. The dependence of photovoltaic and charge transport parameters in these ambipolar semiconductors on the specific molecular structure is investigated before and after post‐treatment by solvent vapor annealing. The inner nanomorphology of the photoactive films of the dyads is analyzed with transmission electron microscopy (TEM) and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS). Combined theoretical calculations result in a lamellar supramolecular order of the dyads with a D–A phase separation smaller than 2 nm. The molecular design and the precise distance between donor and acceptor moieties ensure the fundamental physical processes operative in organic solar cells and provide stabilization of D–A interfaces.

Structure-properties relationships in triarylamine-based push-pull systems-C60 dyads as active material for single-material organic solar cells

The synthesis of a dyad involving a small arylamine-dicyanovinyl push-pull system as donor block and C60 fullerene as acceptor, connected by a flexible insulating linker formed by esterification of a β-hydroxymethylthiophene spacer is described. Unlike previously reported parent dyads with linkers connected at the 2-position of the thienyl spacer, this mode of connection allows the preservation of a free carbaldehyde group and thus the possibility to modulate the energy levels of the push-pull donor block. The electronic properties of the new dyad are analyzed by UV–Vis absorption spectroscopy, cyclic voltammetry, and theoretical calculations. A preliminary evaluation of this compound as active material for single-material organic solar cells is reported and discussed with reference to the mode of linkage of donor and C60 blocks.

Star-shaped benzotriindole-based donor-acceptor molecules: Synthesis, properties and application in bulk heterojunction and single-material organic solar cells

The search of the novel building blocks for π-conjugated donor-acceptor (D-π-A) molecules remains an urgent task to design promising materials for organic solar cells (OSCs) and other electronic devices. Here we report on the design and synthesis of two star-shaped D-π-A small molecules based on benzotriidole (BTI) electron-donating core, BTI(2T-DCV-Hex)3 and BTI(2T-CNA-EHex)3, end-capped with either hexyldicyanovinyl or 2-ethylhexylcyanoacetate acceptor groups. Comprehensive investigation and comparison of the optical, thermal and physicochemical properties of these molecules and their analogue with the triphenylamine (TPA) core, N(Ph-2T-DCV-Hex)3, revealed the effect of the electron-withdrawing groups and type of the donor core on their properties. The BTI-based material BTI(2T-DCV-Hex)3 differs from the amorphous TPA-based analogue by high crystallinity and blue-shifted absorption and luminescence spectra. The change of electron-withdrawing group from hexyldicyanovinyl to 2-ethylhexylcyanoacetate leads to a higher energy of the lowest unoccupied molecular orbital, lower solubility and several times higher photoluminescence quantum yield in solutions achieving 67%. Evaluation of the photovoltaic performance of these materials in single-material OSCs and as a donor material in bulk heterojunction OSCs with PC71BM as an acceptor revealed that the devices based on BTI(2T-DCV-Hex)3 are more efficient as compared to those based on BTI(2T-CNA-EHex)3. In comparison to N(Ph-2T-DCV-Hex)3, the photovoltaic devices based on BTI(2T-DCV-Hex)3 showed the comparable performance in bulk heterojunction OSCs and two times higher performance (about 1%) in single-material OSCs. As a result, we conclude that the BTI core is a promising block for the design of semiconducting materials for organic photovoltaics and other related applications.

Single-material organic solar cells with fully conjugated electron-donor alkoxy-substituted bithiophene units and electron-acceptor benzothiadiazole moieties alternating in the main chain

Main chain conjugated linear polymers, constituted by alternating electron-donor (D) and -acceptor (A) moieties, have been prepared with the aim of testing their performances as photoactive components in single material organic solar cells (SMOSCs).

Evaluation of covalently linked (bacterio)chlorin-fullerenes as components for organic solar cells

A series of (bacterio)chlorophyll derivatives covalently linked with fullerenes were synthesized to explore their potential as donor–acceptor conjugates to organic solar cells (OSCs). Their physical properties and photovoltaic performances were investigated and compared with (bacterio)chlorins without fullerenes. A weak intramolecular interaction between the (bacterio)chlorin chromophore and the fullerene unit(s) was observed in their electronic absorption spectra in solution, and efficient fluorescence quenching occurred in their monomeric states. All the (bacterio)chlorin-fullerene conjugates worked as components for single material OSCs and the best power conversion efficiency of 0.62% with [Formula: see text] mA cm[Formula: see text], [Formula: see text] V, and [Formula: see text] was achieved for chlorin-C3-methyl phenyl-C[Formula: see text]-butylate, DA-2.

Charge photogeneration and recombination in single-material organic solar cells and photodetectors based on conjugated star-shaped donor-acceptor oligomers

Abstract Single-material organic solar cells (SMOSC) are attracted by their simple structure and ease of fabrication so that they are virtually free from a number of drawbacks of heterojunction organic solar cells. However, the performance of SMOSC is still low, first of all because of poor understanding of losses on the way of energy conversion from light to electricity. In this work, we present solution-processed SMOSC based on star-shaped π-conjugated donor-acceptor oligomers with triphenylamine donor (N-Ph3) and alkyl- or phenyl dicyanovinyl acceptor (DCV-R) of general formulae N(Ph-nT-DCV-R)3, where nT stands for n-oligothiophene, and study charge photogeneration and recombination in them. SMOSC demonstrate small energy losses resulting in high open-circuit voltage of 1.08–1.19 V and the power conversion efficiency up to 1.22% under illumination intensity of 0.45 sun (1.13% under one sun) with the maximum external quantum efficiency up to 24% for N(Ph-2T-DCV-Ethyl)3, which are among the highest for SMOSC based on conjugated donor-acceptor small molecules or oligomers. It was found that monomolecular recombination dominates at the short-circuit condition and the maximum power point, but at the open-circuit condition the photoinduced charges recombine nearly bimolecularly. The bottleneck in the SMOSC performance was shown to be the field-assisted charge generation perfectly described by the Onsager model in the limit of weak electric fields. The results obtained suggest that intermolecular charge delocalization in conjugated donor-acceptor molecules would be beneficial for further progress in SMOSC.

Effect of Electron-Acceptor Content on the Efficiency of Regioregular Double-Cable Thiophene Copolymers in Single-Material Organic Solar Cells.

Three regioregular thiophenic copolymers, characterized by a bromine atom or a C60-fullerene group at different molar ratios at the end of a decamethylenic plastifying side chain, have been successfully synthesized using a straightforward postpolymerization functionalization procedure based on a Grignard coupling reaction. Owing to their good solubility in common organic solvents, the products were fully characterized using chromatographic, spectroscopic, thermal, and morphological techniques and used as single materials in the photoactive layers of organic solar cells. The photoconversion efficiencies obtained with copolymers were compared with those of a reference cell prepared using a physical blend of the precursor homopolymer and [6,6]-phenyl-C61-butyric acid methyl ester. The best results were obtained with COP2, the copolymer with a 21% molar content of C60-functionalized side chains. The use of the double-cable polymer made possible an enhanced control on the nanomorphology of the active blend, thus reducing phase-segregation phenomena as well as the macroscale separation between the electron-acceptor and -donor components, yielding a power conversion efficiency higher than that of the reference cell (4.05 vs 3.68%). Moreover, the presence of the halogen group was exploited for the photo-cross-linking of the active layer immediately after the thermal annealing procedure. The cross-linked samples showed an increased stability over time, leading to good efficiencies even after 120 h of accelerated aging: this was a key feature for the widespread practical applicability of the prepared devices.

C60-small arylamine push-pull dyads for single-material organic solar cells

The synthesis of two dyads involving small arylamine-based push-pull systems as donor block and C60 fullerene as acceptor connected by a flexible insulating linker formed by esterification is described. After analysis of their electronic properties by cyclic voltammetry and UV–Vis absorption spectroscopy, the potential of these molecules as active material for single-material organic solar cells has been evaluated in simple devices of direct structure. Both dyads lead to modest conversion efficiencies of ∼0.40% due essentially to poor fill factors. These results are discussed in terms of insufficient nano-phase separation of the donor and acceptor blocks and of fall of hole-mobility of the donor block consecutive to the linking to C60.

A major step toward efficient and stable single-material organic solar cells

A major step toward efficient and stable single-material organic solar cells

Covalently linked donor-acceptor dyad for efficient single material organic solar cells.

A novel covalently linked donor-acceptor dyad comprising a dithienopyrrol-based oligomeric donor and a fullerene acceptor was synthesized and characterized. The concomitant effect of favorable optoelectronic properties, energy levels of the frontier orbitals, and ambipolar charge transport enabled the application of the dyad in simplified solution-processed single material organic solar cells reaching a power conversion efficiency of 3.4%.