Search

Perovskite interfaces critically influence the final performance of the photovoltaic devices. Optimizing them by reducing the defect densities or improving the contact with the charge transporting material is key to further enhance the efficiency and stability of perovskite solar cells. Inverted (p-i-n) devices can particularly benefit here, as evident from various successful attempts. However, every reported strategy is adapted to specific cell structures and compositions, affecting their robustness and applicability by other researchers. In this work, we present the universality of perovskite top surface post-treatment with ethylenediammonium diiodide (EDAI

The planar-zigzag shape of polymers leads to a face-on orientation of the main chains in thin films which improves the photovoltaic performance through better absorption coefficients, charge carrier generation, and collection efficiency.

Carrier extraction in mixed tin–lead perovskite solar cells is improved by modifying the top and bottom perovskite surfaces with ethylenediammonium diiodide and glycine hydrochloride, respectively. Trap densities in perovskite layers are reduced as a result of surface passivation effects and an increase in film crystallinity. In addition, the oriented aggregation of the ethylenediammonium and glycinium cations at the charge collection interfaces results in the formation of surface dipoles, which facilitate charge extraction. As a result, the treated mixed tin–lead perovskite solar cells showed improved performance, with a fill factor of 0.82 and a power conversion efficiency of up to 23.6%. The unencapsulated device also shows improved stability under AM1.5 G, retaining over 80% of the initial efficiency after 200 h continuous operation in an inert atmosphere. Our strategy is also successfully applied to centimeter-scale devices, with efficiencies of up to 21.0%., スズを含むペロブスカイト太陽電池：23.6%の世界最高効率を達成 --ペロブスカイト薄膜の上下表面構造修飾法を開発--. 京都大学プレスリリース. 2022-04-13.

The backbone shape of semiconducting polymers strongly affects their electronic properties and morphologies in films, yet the conventional design principle for building blocks focuses on using linear main chains to maintain high crystallinity. Here, we developed a V-shaped unit, triphenyleno[1,2-c:7,8-c']bis([1,2,5]thiadiazole) (TPTz), featuring two 1,2,5-thiadiazole rings fused to a triphenylene core with strong electron-withdrawing properties and an extended conjugation plane. We used TPTz to prepare a highly soluble copolymer, PTPTz-indacenodithiophene (IDT), which exhibited a wide bandgap of 1.94 eV and energy levels suitable for the donor polymer in organic solar cells (OSCs) in combination with non-fullerene acceptors. Despite the amorphous nature of the polymer film, single-junction OSCs with PTPTz-IDT:Y6 as the active layer achieved a power conversion efficiency of 10.4% (JSC = 19.8 mA cm-2; VOC = 0.80 V; fill factor = 0.66), which is the highest value reported for a single-junction OSC with IDT-based donor polymers. This work demonstrates that TPTz is a promising electron-acceptor unit for developing functional polymers with zigzag structures.

To improve the performance of organic field-effect transistors (OFETs) employing π-conjugated polymers, a basic understanding of the relationships between the material properties and device characteristics is crucial. Although the density of states (DOS) distribution is one of the essential material properties of semiconducting polymers, insights into how the DOS shape affects the mobility (µ), subthreshold swing (S), and contact resistance (R

Polymer-blend solar cells (all-PSCs) based on a copolymer of naphthodithiophene diimide and bithiophene (PNDTI-BT-DT) as a near-infrared absorber as well as an electron acceptor were fabricated in combination with PTB7 as an electron donor. Notably, the external quantum efficiency spectra of the all-PSCs demonstrated photoresponse up to 900 nm with the efficiency of 25% at 800 nm, which is much higher than that for the previously reported all-PSCs. Power conversion efficiency as high as 2.59% was achieved under the irradiation of simulated solar light (AM1.5, 100 mW/cm2). Both PNDTI-BT-DT and PTB7 formed a crystalline structure in the blend films similar to in the pristine films, leading to the efficient charge generation contributed from both polymers.

Three isomeric derivatives of 2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1

Surface modification of SiO2 using a catalyst-free quantitative reaction between an amine and an ethynyl-π-extended naphthalenediimide was investigated. A post-reaction method, in which the catalyst-free reaction was performed at the surface after the formation of amino-terminated self-assembled monolayers (SAMs), resulted in dense, uniform modification of the SiO2 surface with the naphthalenediimide molecules. Both X-ray reflectivity and angle-resolved X-ray photoemission spectroscopy showed consistent results for the layer thickness and density. In contrast, a pre-reaction method, in which an amino-silane and the ethynyl-π-extended naphthalenediimide reacted first and then formed a SAM, afforded a sparse SAM on the SiO2 surface, probably due to the steric hindrance of the naphthalenediimide moieties. The in situ decoration of the SiO2 surface by a catalyst-free quantitative reaction offers a facile route for modifying surface properties with various π-conjugated molecules suitable for many applications.

A new π-conjugated polymer based on naphthalenediimide with a branched semifluoroalkyl side chain (FNDIT2) was synthesized and used to change the polymer orientations in thin films. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy revealed that FNDIT2 spontaneously forms surface-segregated monolayers in blend films with other π-conjugated polymers to adopt a preferred face-on orientation, with the π-plane of the polymer aligned more parallel to the surface. Thermal annealing of the films induced further reorientation of the polymers inside the films closer to the face-on orientation, as shown by two-dimensional grazing-incidence wide-angle X-ray scattering. The induced face-on orientations in the films led to higher charge mobility in the vertical direction. This study provides a general and versatile strategy to control the molecular orientation in thin films and enhance the performance of thin-film organic electronics.

The chirality of organic semiconductors is important for various applications in optoelectronics and spintronics. Here, we propose a new strategy to induce structural chirality in achiral organic semiconductors in thin films. Enantiomeric fullerene derivatives (S)-pSi and (R)-pSi, which have oligo(dimethylsiloxane) as a low-surface-energy moiety, were synthesized and used as surface-segregated monolayers (SSMs) in spin-coated films of several achiral fullerene derivatives. Upon thermal annealing, the presence of the chiral SSMs led to the crystallization of the fullerenes in the films as an SSM-induced crystal phase at lower temperatures. The crystallized films showed circular dichroism ascribed to the fullerene absorption, the sign and the intensity of which depended on the handedness of the SSM molecules and the film thickness, respectively. These results indicate that the achiral fullerene derivatives in the films were induced by the SSMs to crystallize into enantiomorphic crystals. Our approach to inducing chirality in organic thin films is compatible with many device applications., Chiral induction: surface-segregated monolayers of chiral molecules induce the enantiomorphic crystallization of achiral fullerene derivatives in thin films.

The backbone shape of semiconducting polymers strongly affects their electronic properties and morphologies in films, yet the conventional design principle for building blocks focuses on using linear main chains to maintain high crystallinity. Here, we developed a V-shaped unit, triphenyleno[1,2

Structural control of organic semiconductor thin films at the interface and in the bulk is vital for their use in various organic electronic devices. In this focus review, we provide an overview of the formation and functions of surface-segregated monolayers (SSMs) on organic semiconductor films. Driven by the low surface energy of the molecules, SSMs are spontaneously formed through molecular self-organization during spin-coating from solution. Careful design of SSM molecules allows the formation of highly ordered surface monolayers with high coverage densities. SSMs can be used to induce changes in the molecular structure and the orientation in the bulk film, which can be exploited to improve the bulk properties of films. Film surfaces covered with SSMs can be used to change the interfacial properties of organic/metal and organic/organic interfaces in various organic electronic devices. These modifications can drastically alter the performance of devices, demonstrating the general importance of interfaces. We conclude the review by discussing directions for further development of SSMs and applications in the field of organic electronic devices. This focus review provides an overview of the formation and functions of surface-segregated monolayers (SSMs) on organic semiconductor films. Careful design of SSM molecules allows the formation of highly ordered surface monolayers with high coverage densities. SSMs can be used to induce changes in the molecular structure and the orientation in the bulk film. SSMs can be used to change the interfacial properties of organic/metal and organic/organic interfaces in various organic electronic devices. These modifications can drastically alter the performance of devices, demonstrating the general importance of interfaces.

Diketopyrrolopyrrole (DPP)-based semiconducting polymers were synthesized with the alkyl side chains of 3,7,11,15-tetramethylhexadec-2-en-1-yl (TMHDe) and 3,7,11,15-tetramethylhexadecyl (TMHD) that...

The growing number of new π-conjugated polymers and small-molecules has promoted the rapid development of organic solar cells (OSCs) over the past two decades. Among the most widely used building blocks, dithieno[3,2-b:2′,3′-d]pyrrole (DTP) and its derivatives have occupied an important position in both electron-rich and electron-deficient semiconductors since their first introduction into photovoltaic materials in 2007. The incorporation of basic DTP units such as N-alkyl DTP, N-acyl DTP and pyrrolo[3,2-d:4,5-d′]bisthiazole (PBTz), and their derivatives including fused DTP, and the lactam and imide conjugated heterocycles into photovoltaic polymers and small-molecules largely enhanced the open circuit voltage (VOC), short-circuit current (JSC), fill factor (FF) and finally power conversion efficiency (PCE) of OSCs. In this review, we provide a comprehensive overview of the progress in DTP-based materials, summarize the current state of DTP research and describe the relationship between the molecular structure and device performance, which could pave a way for the further rational design of novel DTP-derived building blocks and the corresponding photovoltaic materials.

Despite the critical importance of the density of states (DOS) to the electrical properties of molecular semiconductors, there are few reliable measurement methods for the DOS, especially for the edge regions with low DOS that determine the charge conduction. Here, we evaluate the DOS for occupied states with high sensitivity (down to 10-5 relative to the peak maxima) using a commercially available photoelectron yield spectroscopy (PYS) system operated in air. The conduction edges of the DOS for both the semiconducting polymers and molecules are expressed as a single Gaussian with no gap states with one exception. There are subtle differences in the widths of the Gaussian for the DOS edges between the surface of the polymer films and the interface with the substrate, which result in the large difference in the lateral charge carrier mobilities at each interface. The charge carrier mobilities of the semiconducting polymers have a correlation with the widths of the DOS. PYS in air is a powerful tool for studying the relationship among the structure and electronic and electrical properties of molecular semiconductors.

A chiral polythiophene surfactant based on poly(3-(S)-2-methylbutylthiophene) ((S)-P3MBT) with a semifluoroalkyl group at one end of the main chain was synthesized and used to form surface-segregated monolayers (SSMs). Films of pure (S)-P3MBT mainly adopted the edge-on orientation, whereas (S)-P3MBT films with a SSM of the polymer surfactant (S)-P3MBT-F17 contained a large proportion of end-on-oriented polythiophene, both at the surface and inside the films. The thin films with the SSM showed circular dichroism signals, with the sign opposite to those observed in (S)-P3MBT films. These findings suggest that the orientation-controlled SSM layers induced changes in the packing of the polymer aggregates in the films, resulting in a dramatic change in the excitonic interactions of the chiral semiconducting polymers.

Flexible organic photovoltaics (OPVs) are promising power sources for wearable electronics. However, it is challenging to simultaneously achieve high efficiency as well as good stability under various stresses. Herein, we demonstrate the fabrication of highly efficient (efficiency, 13.2%) and stable OPVs based on nonfullerene blends by a single-step postannealing treatment. The device performance decreases dramatically after annealing at 90 °C and is fully recovered after annealing at 150 °C. Glass-encapsulated annealed OPVs show good environmental stability with 4.8% loss in efficiency after 4,736 h and an estimated T(80) lifetime (80% of the initial power conversion efficiency) of over 20,750 h in the dark under ambient condition and T(80) lifetime of 1,050 h at 85 °C and 30% relative humidity. This environmental stability is enabled by the synergetic effect of the stable morphology of donor/acceptor blends and thermally stabilized interfaces due to doping. Furthermore, the high efficiency and good stability are almost 100% retained in ultraflexible OPVs and minimodules which are mechanically robust and have long-term operation capability and thus are promising for future self-powered and wearable electronics.

The bulk photovoltaic effect (BPVE) has drawn intensive attention due to its unique features that cannot be accessed with the conventional photovoltaic effect. However, the BPVE is observed in noncentrosymmetric materials and has been studied mainly for inorganic materials. Here, we report a simple subphthalocyanine (SubPc) derivative that assembles into a noncentrosymmetric columnar liquid crystal with the help of a DC E-field. These columnar assemblies exhibit the BPVE over a wide range of wavelengths up to 650 nm. Furthermore, just by sandwiching this columnar assembly between two ITO electrodes, the resultant device reaches a light-on/off ratio, Ilight/Idark, as high as 6.6 × 103, indicating that the polar columnar assemblies with SubPcs are promising for photodetectors.

Ultrathin (thickness less than 10 µm) organic photovoltaics (OPVs) can be applied to power soft robotics and wearable electronics. In addition to high power conversion efficiency, stability under various environmental stresses is crucial for the application of ultrathin OPVs. In this study, the authors realize highly air-stable and ultrathin (≈3 µm) OPVs that possess high efficiency (15.8%) and an outstanding power-per-weight ratio of 33.8 W g

Designing donor/acceptor (D/A) interfaces that can efficiently generate free carriers is an attractive research target for organic photovoltaics (OPVs). While many reports suggest that the molecular orientation of the donor at the D/A interface influences the free-charge generation and recombination, the effects of the acceptor orientation on these processes remain elusive. In this work, we demonstrate that [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) changes its molecular orientation at the film surface on crystallization, resulting in the preferential surface exposure of the side chains. Photoelectron spectra of amorphous- and crystalline-PC61BM/sexithiophene (6T) interfaces and analysis of the external quantum efficiency and electroluminescence of bilayer OPVs in the charge-transfer absorption range reveal that the orientational change of PC61BM raises the energy of the charge-transfer state at the D/A interface. In addition, the PC61BM side chain at the crystalline-PC61BM/6T interface reduces t...

Next-generation biomedical devices1-9 will need to be self-powered and conformable to human skin or other tissue. Such devices would enable the accurate and continuous detection of physiological signals without the need for an external power supply or bulky connecting wires. Self-powering functionality could be provided by flexible photovoltaics that can adhere to moveable and complex three-dimensional biological tissues1-4 and skin5-9. Ultra-flexible organic power sources10-13 that can be wrapped around an object have proven mechanical and thermal stability in long-term operation13, making them potentially useful in human-compatible electronics. However, the integration of these power sources with functional electric devices including sensors has not yet been demonstrated because of their unstable output power under mechanical deformation and angular change. Also, it will be necessary to minimize high-temperature and energy-intensive processes10,12 when fabricating an integrated power source and sensor, because such processes can damage the active material of the functional device and deform the few-micrometre-thick polymeric substrates. Here we realize self-powered ultra-flexible electronic devices that can measure biometric signals with very high signal-to-noise ratios when applied to skin or other tissue. We integrated organic electrochemical transistors used as sensors with organic photovoltaic power sources on a one-micrometre-thick ultra-flexible substrate. A high-throughput room-temperature moulding process was used to form nano-grating morphologies (with a periodicity of 760 nanometres) on the charge transporting layers. This substantially increased the efficiency of the organophotovoltaics, giving a high power-conversion efficiency that reached 10.5 per cent and resulted in a high power-per-weight value of 11.46 watts per gram. The organic electrochemical transistors exhibited a transconductance of 0.8 millisiemens and fast responsivity above one kilohertz under physiological conditions, which resulted in a maximum signal-to-noise ratio of 40.02 decibels for cardiac signal detection. Our findings offer a general platform for next-generation self-powered electronics.

Precise control of the molecular arrangements at the interface between the electron donor and acceptor in mixed bulk heterojunctions (BHJs) remains challenging, despite the correlation between structural characteristics and efficiency in organic photovoltaics (OPVs). This study reveals that the substitution patterns of linear and branched alkyl side chains on electron-donating/-accepting alternating copolymers can control the positions of an acceptor molecule (C60 ) around the π-conjugated main chains in mixed BHJs. Two-dimensional solid-state NMR demonstrates a marked difference in the location of C60 in the blend films. A copolymer with an electron-accepting unit positioned in close proximity to C60 demonstrated higher OPV performance in combination with various fullerene derivatives. This molecular design offers precise control over the interfacial molecular structure, thereby paving the way for overcoming the current limitations of OPVs comprising mixed BHJs.

Surface-segregated monolayers (SSMs) based on two poly(3-alkylthiophene)s with semifluoroalkyl groups at either the side chains (P3DDFT) or one end of the main chain (P3BT-F17) were used as self-organized buffer layers at the electrode interfaces in bulk heterojunction (BHJ) organic photovoltaic devices. Both of the SSMs greatly shifted the vacuum levels of the BHJ films at the surface due to the aligned permanent dipole moments of the semifluoroalkyl chains. Hole extraction in the BHJ of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) became more efficient in the presence of the P3DDFT buffer layer, resulting in an improved power conversion efficiency. In contrast, the SSM of P3BT-F17 induced changes in the chain orientation of P3HT and the morphology of the BHJ films, resulting in decreased performance. These results indicate that the molecular design of polymer-based SSMs can affect not only the energy structure at the interface but also the morphology and the molecular ...

Understanding molecular diffusion across the interfaces in planar heterojunctions is fundamentally important to improving the performance and stability of organic electronic devices. In this study, we quantitatively evaluated the diffusion of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) across the interface of planar heterojunctions into the polymer layers by time-of-flight secondary ion mass spectroscopy. Careful calibration allowed the concentration of PCBM to be determined in the polymer layer at concentrations as low as 0.01 wt %. We found that approximately 1 wt % PCBM was present in the poly(3-hexylthiophene) layer in the planar heterojunction with no thermal treatments, indicating that a small amount of PCBM diffused into the polymer layer even at room temperature. The diffusion behavior depended strongly on the crystallinity of the PCBM layer and the properties of the polymer layers such as glass transition temperature. Further analysis suggested that the diffusion of PCBM into the polymer layers was also related to the interface free energy between the layers.

Recent progress in organic photovoltaics (OPVs) has led to an increased importance of laboratory-scale fabrication in ambient air using solution processes. However, the effect of the existence of both ambient air and light during the formation of a photoactive layer on the performance of fabricated devices has not been elucidated thus far in detail. Here, we show that photoactive layer formation in completely dark conditions enables air-processable OPVs with a high power conversion efficiency. The degradation in OPV performance caused by the coexistence of air and room light was confirmed by systematically examining atmospheric and room-light irradiation conditions during the formation and drying of the photoactive layer. Moreover, the degradation rate was much faster than that in the case of dried solid photoactive layers exposed to room light in ambient air. The photoactive layer with non-fullerene acceptors showed a much slower degradation rate, owing to room light, than that with fullerene acceptors. Based on these findings, we demonstrate that by eliminating light during formation, slot-die-coated OPVs in ambient air show comparable performance to that of spin-coated OPVs in an inert glovebox.

On the basis of naphthalene diimide (NDI) units connected to thiophene (T), thienothiophene (TT), or dithienothiophene (DTT) units via a thiophene π-bridge, three new copolymers-PDTNDI-T, PDTNDI-TT, and PDTNDI-DTT, respectively-were synthesized and used in the fabrication of all-polymer solar cells (all-PSCs). The relationships between the structures of the polymers and their optoelectronic properties and photovoltaic performances as electron acceptors in all-PSCs were investigated in detail. As the number of copolymerized heteroaromatic rings in the DTNDI-based polymers increased, the power conversion efficiencies of the resulting all-PSCs were found to decrease. This decreasing trend in the photovoltaic performance is opposite to the results reported previously for NDI-based polymers lacking the thiophene π-bridge and naphthodithiophene diimide-based polymers. In addition, the three polymers were found to exhibit distinct molecular orientations: a face-on orientation for PDTNDI-T and edge-on orientations for PDTNDI-TT and PDTNDI-DTT. Our results indicate that large fused aromatic rings are not necessarily advantageous in the design of NDI-based polymers containing π-conjugated bridges.

In this research, a haptacyclic carbazole-based dithienocyclopentacarbazole (DTCC) ladder-type structure was formylated to couple with two 1,1-dicyanomethylene-3-indanone (IC) moieties, forming a new nonfullerene acceptor DTCCIC-C17 using a bulky branched 1-octylnonayl side chain at the nitrogen of the embedded carbazole and four 4-octylphenyl groups at the sp3-carbon bridges. The rigid and coplanar main-chain backbone of the DTCC core provides a broad light-absorbing window and a higher-lying LUMO energy level, whereas the bulky flanked side chains reduce intermolecular interactions, making DTCCIC-C17 amorphous with excellent solution processability. The DTCCIC-C17 as an acceptor is combined with a medium band gap polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T) as the donor in the active layer to obtain suitable highest occupied molecular orbital/lowest u...

Single-walled carbon nanotubes (SWCNTs) have received much attention because of their potential in optoelectronic applications. Pristine SWCNTs exhibit substantial van der Waals interactions and hydrophobic characteristics, so precipitation occurs immediately in most organic solvents and water. Highly toxic and hazardous chemicals are often used to obtain well-dispersed SWCNTs. Developing environmentally friendly processing methods for safe and practical applications is a great challenge. Here, we demonstrate direct exfoliation of SWCNTs in pure water only with n-type semiconducting fullerene nanoparticles. The resultant SWCNTs can be well-dispersed in water, where they remain essentially unchanged for several weeks. Adding an aqueous solution of p-type semiconducting water-soluble polythiophene yields self-assembled p/n heterojunctions between polythiophene and the nanoparticles. The aqueous-dispersed SWCNTs yield photocurrent responses in solution-processed thin films as a potential application of water-dispersed carbon nanomaterials.

Semiconducting copolymers based on benzo[1,2-b:4,5-b′]dithiophene and thieno[3,4-c]pyrole-4,6-dione containing oligo(thienylenevinylene) side chains with different lengths were synthesized to examine the effect of the π-conjugated side chains on the performance of polymer solar cells (PSCs). Using the copolymers that had π-conjugated side chains as the PSC electron donor resulted in a higher short circuit current and fill factor compared with the reference copolymers, which had no side chain or an analogous side chain with no π-conjugation, resulting in an increase of power conversion efficiency of 10–22%. Measurements of hole mobility by space-charge-limited current and internal quantum efficiency indicated that introducing the π-conjugated side-chain units can facilitate both charge transport and charge separation in the polymer:PC71BM blend films.