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The electro-active third component (BID)-incorporated PM6-B10-based organic solar cell shows a high performance (PCE = 17.2%) and mechanical stretchability (COSavg = 11.4%), outperforming the PM6-based device (PCE = 15.8%, COSavg = 2.0%).

The damp-heat stability and photostability of solar cells were investigated depending on the ZnO fabrication methodology. Although the initial PCEs of the devices were similar, the ZnOs affected the solar cell performance after the aging process.

A strategy to obtain low Jd in OPDs from a material point of view is presented: fluorination of the electron donor unit in a donor–acceptor type conjugated polymer is an effective way to reduce the Jd of OPDs by suppressing the trap DOS.

Solution-processed near-infrared (NIR)-absorbing organic solar cells (OSCs) have been explored worldwide because of their potential as donor:acceptor bulk heterojunction (BHJ) blends. In addition, NIR-absorbing OSCs have attracted attention as high specialty equipment in next-generation optoelectronic devices, such as semitransparent solar cells and NIR photodetectors, owing to their feasibility for real-time commercial application in industry. With the introduction of NIR-absorbing non-fullerene acceptors (NFAs), the value of OSCs has been increasing while organic donor materials capable of absorbing light in the NIR region have not been actively studied yet compared to NIR-absorbing acceptor materials. Therefore, we present an overall understanding of NIR donors.

Ternary-blend active layers composed of one donor and two acceptors have been actively studied to enhance the power conversion efficiency (PCE) of organic solar cells (OSCs), and numerous advances ...

In this article, two D–A-type quinoxaline-based polymers with multiple fluorine atoms, denoted by PB-QxF and PBF-QxF, were synthesized and tested for polymer solar cells (PSCs). Owing to the excellent optical, electrochemical, and charge transport properties of these polymers, impressive PCEs of 10.99 and 13.96% were achieved by the inverted-type lab-scale spin-coated devices based on PB-QxF and PBF-QxF, respectively, in the presence of a nonfullerene Y6 acceptor. In addition, to evaluate the feasibility of the process for mass production, a scalable roll-to-roll (R2R) slot-die coating process was attempted to fabricate PSCs on flexible substrates. Notably, the best PCE of 9.63% was obtained using an R2R processed additive-free PSC based on PBF-QxF, which is the highest value among all R2R processed PSCs. Moreover, the device with PBF-QxF exhibited good thickness tolerance to PCE up to 350 nm, which is one of the key requirements for R2R compatible materials.

Tandem device architectures offer a route to greatly increase the maximum possible power conversion efficiencies (PCEs) of polymer solar cells, however, the complexity of tandem cell device fabrication (such as selecting bandgaps of the front and back cells, current matching, thickness, and recombination layer optimization) often result in lower PCEs than are observed in single‐junction devices. In this study, we analyze the influence of front cell and back cell bandgaps and use transfer matrix modeling to rationally design and optimize effective tandem solar cell structures before actual device fabrication. Our approach allows us to estimate tandem device parameters based on known absorption coefficients and open‐circuit voltages of different active layer materials and design devices without wasting valuable time and materials. Using this approach, we have investigated a series of wide bandgap, high voltage photovoltaic polymers as front cells in tandem devices with PTB7‐Th as a back cell. In this way, we have been able to demonstrate tandem devices with PCE of up to 12.8% with minimal consumption of valuable photoactive materials in tandem device optimization. This value represents one of the highest PCE values to date for fullerene‐based tandem solar cells.

Small-bundled single-walled carbon nanotube (SSWCNT) nanocomposite films with two different conjugated polymers were facilely prepared by using a micronizing mill. The influence of the difference i...

Herein, we introduce for the first time that Cs2CO3 can work with SnO2 based on a facile low-temperature solution-processed as dual electron transport layers (ETL) for enhancing device performance of inverted organic solar cells (iOSCs). Aside from better morphologies, a lower work function of ETLs, and an efficient charge extraction, along with a much lower transport resistance at the interfaces are found for iOSCs using SnO2/Cs2CO3 rather than devices based on the SnO2 only. The iOSC devices with P3HT:PC60BM as an active layer, using SnO2/Cs2CO3 (0.5 mg/ml) as dual ETLs, achieved a champion power conversion efficiency (PCE) of 3.75%, which is >36% higher than that of only the based SnO2 (2.75%). Moreover, their PCEs remained at ∼94% of the initial values after storage for 4 weeks in ambient air without any encapsulations, thus demonstrating the excellent long-term device stability. Notably, for the PTB7-Th:PC70BM systems, we also achieved an impressive champion PCE of 7.78% with using SnO2/Cs2CO3 (0.5 mg/ml) as dual ETLs, meanwhile devices based on SnO2 only exhibited a humble PCE of 4.08%. We believe that SnO2/Cs2CO3 dual ETLs concept can also be applied to other optoelectronic devices such as perovskite solar cells or light-emitting diodes, where an ETL is required to ensure high efficiency.

One of the key components in inverted organic solar cells is a zinc oxide (ZnO) layer as an electron-extraction layer. However, this layer contains electron traps that decrease the electron-extraction efficiency and reduce the photovoltaic performance. In this work, we report the photovoltaic property improvement of inverted PTB7-Th:PC71BM solar cells by coating high-molecular-weight poly(N-isopropylacrylamide-co-methacrylic acid) (H-PNIPAM) on top of the ZnO layer. The H-PNIPAM film thicknesses were carefully controlled by spin-coating different concentrations of H-PNIPAM solutions to generate an optimal thickness (3–5 nm). Atomic force microscopy and X-ray photoelectron spectroscopy revealed a uniformly coated H-PNIPAM layer. The photoluminescence spectra showed that the layer reduced the number of ZnO trap states. Contact angle measurements indicated that the layer modified the ZnO surface to become more hydrophobic, resulting in good contact with photoactive films. At the same time, the treatment decr...

The mechanism of magnetoconductance (MC) in organic solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) remains unclear. Recombination of polaron pairs in the P3HT:PCBM organic solar cell is important in view of MC as well as charge transportation. To examine whether the polaron-pair model explains the mechanism of MC in the P3HT:PCBM system, we used an equivalent circuit model in which the internal shunt resistance represents the polaron-pair recombination. The almost identical dependence of the MC and the magnetic field effect on the internal shunt resistance for the P3HT:PCBM solar cells with various polaron-pair recombination rates clearly shows that the MC is ascribed to the polaron-pair recombination. Furthermore, the fact that the MC is virtually unaffected by light intensity below 100 mW/cm2 confirms that the polaron pairs responsible for the MC are geminate. The circuit model provides a useful instrument for probing the polaron-pair recombination in the system where excitons are effectively quenched.

We developed p-n junction organic photodetectors (OPDs) composed of a polymer donor and a nonfullerene acceptor (NFA) to increase both the responsivity (R) and detectivity (D*) while maintaining a narrow wavelength selectivity. The selection of the polymer donor and NFA with similar green (G) absorption is important for achieving G-wavelength selectivity in these OPDs, which differentiates them from current fullerene-based OPDs and NFA-based panchromatic absorption OPDs. In addition, mixing the polymer donor and asymmetric NFA was efficient toward increasing the miscibility and decreasing the interfacial energy difference of the blended films, resulting in the formation of a uniform and well-mixed nanomorphology in the photoconductive layer. Two-dimensional (2D) grazing incidence X-ray diffraction and Fourier-transform infrared spectroscopy revealed that the lamellar ordering of the polymer donor was enhanced in the blend film prepared with an asymmetric NFA, whereas the aggregation of a symmetric NFA in the blend films did not increase the lamellar ordering of the polymer donor. Consequently, we achieved an R value of 0.31 A/W and D* value of 2.0 × 1013 Jones with a full width at half-maximum value of 230 nm at -2 V and fast response time of 27 μs without any external bias in the asymmetric NFA-based OPDs. The enhancement in the lamellar ordering and miscibility of the blended films are crucial toward increasing the static and dynamic properties of OPDs.

We report the synthesis of composite interlayers by using alcohol-soluble polyfluorene-wrapped single-walled carbon nanotubes (ASP-wrapped SWNTs) and their application to the electron transport layer in efficient organic solar cells. The ASP enable the individual dispersion of SWNTs in solution. Impressively, ASP-wrapped SWNTs solutions are stable for 54 days, indicating very high dispersion stability. Using the ASP-wrapped SWNTs as a cathode interlayer on zinc oxide nanoparticles (ZnO NPs), 9.45% of power conversion efficiency (PCE) can be obtained in PTB7-th:PC71BM-based organic solar cells, which is mainly attributed to the improvement of the short circuit current. Performance enhancements of 18% and 17% were achieved compared to those of pure ZnO NPs and ASP on ZnO NPs, respectively. The improvement of solar cell performance originates from an increased internal quantum efficiency, balanced mobility between electrons and holes, and minimization of charge recombination.

Creating an orthogonal printable hole-transporting layer (HTL) without damaging the underlying layer is still a major challenge in fabricating large-area printed inverted polymer solar cells (PSCs). In this study, we prepared orthogonal-processable fluorine-functionalized reduced graphene oxide (FrGO) series with various two-dimensional sheet sizes such as large-sized FrGO (1.1 μm), medium-sized FrGO (0.7 μm), and small-sized FrGO (0.3 μm) and systematically investigated the size effect of FrGOs on the hole transport properties of PSCs. The FrGOs exhibit highly stable dispersion without change over 90 days in 2-propanol solvent, indicating very high dispersion stability. Decreasing the sheet size of FrGOs enhanced hole-transporting properties, resulting in power conversion efficiencies (PCEs) of 9.27 and 9.02% for PTB7-Th:EH-IDTBR- and PTB7-Th:PC

We report the synthesis of composite interlayers using alcohol-soluble polyfluorene (ASP)-wrapped single-walled carbon nanotubes (SWNTs) and their application as electron-transport layers for efficient organic solar cells. The ASP enables the individual dispersion of SWNTs in solution. The ASP-wrapped SWNT solutions are stable for 54 days without any aggregation or precipitation, indicating their very high dispersion stability. Using the ASP-wrapped SWNTs as a cathode interlayer on zinc oxide nanoparticles (ZnO NPs), a power conversion efficiency of 9.45% is obtained in PTB7-th:PC

The technology to record image information at high resolution is of great importance in the optical areas of applied physics and biochemical imaging, as well as in commercial imaging applications such as cameras and machine vision. Organic semiconductors are drawing interest as photodetecting materials for next-generation high-resolution image sensors (IS) owing to their excellent properties such as high absorption coefficient, and color tunability and cost-effective manufacturability. These advantages offer the potential to exceed the technical limitation of silicon-based IS. This article reviews the state-of-the-art technologies of materials and devices in solution-processed organic photodiodes (OPDs) to meet the demands for future high-resolution ISs, which involves challenges ranging from the absence of a fundamental understanding of OPDs to commercialization requirements. Further, this article overviews the progress in the industry as well as academic society. The various requirements and technologies for the development of color-filter-free OPDs with narrow-wavelength detection are also discussed. This review concludes with an outlook of advances in these materials and devices to open up new commercialization routes.

Organic photodetectors (OPDs) are attracting attention for use in flexible and portable electronic applications such as image sensors, remote sensing, optical communications, and medical sensors because of their strong photon responsivity in thin films over a broad range of wavelengths. In particular, the efficient photon-to-current conversion of OPDs under visible light allows their use in indirect X-ray detectors using scintillators to convert X-rays to visible light. The polymer poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b:4,5- b']dithiophene- co-5-(2-hexyldecyl)-1,3-bis(6-octylthieno[3,2- b]thiophen-2-yl)-4 H-thieno[3,4- c]pyrrole-4,6(5 H)-dione) (PBDTT-8ttTPD) shows strong absorption bands in the region of 500-650 nm, as well as high hole mobility, which provides excellent photoresponsivity and photon-to-current conversion efficiency. A p-n junction photodetector was fabricated by blending PBDTT-8ttTPD and [6,6]-phenyl C

The julolidine based interfacial modifier (IM-J) for cathode buffer layer following the "donor-acceptor" design concept with julolidine substituent as an electron donating moiety was incoporated to improve the surface properties of ZnO. Simple treatment of metal oxide type cathode buffer materials with organic interfacial modifier induces the enhanced photovoltaic performance and could effectively overcome several interfacial problems in inverted organic photovoltaic cells (I-OPVs). We studied on the coverage of IM-J on ZnO surface with variation of solution concentrations to reduce charge recombination and macroscopic phase separation. At the optimum condition, ZnO/IM-J (0.05 w/v%), IM-J significantly decreased the surface tension (46.1 mN/m) and improved surface morphology (RMS roughness: 0.61 nm). As a result, compared to the unmodified ZnO based device, the ZnO/IM-J based I-OPVs showed significantly improved power conversion efficiency (PCE) from 7.41 to 8.07% due to the increased photocurrent density (Jsc) and fill factor (FF). It is concluded that IM-J is one of the promising candidates for controlling electronic property of ZnO buffer layer in inverted organic photovoltaic cells. Also, our interfacial modified system can be utilized in other optoelectronic devices.

Porphyrin derivatives have recently emerged as hole transport layers (HTLs) because of their electron-rich characteristics. Although several successes with porphyrin-based HTLs have been recently reported, achieving excellent solar cell performance, the chances to improve this further by molecular engineering are still open. In this work, Zn porphyrin (PZn)-based HTLs were developed by conjugating fluorinated triphenylamine (FTPA) wings at the perimeter of the PZn core for low-temperature perovskite solar cells (L-PSCs). The fluorinated PZn-HTLs (PZn–2FTPA and PZn–3FTPA) exhibited superior HTL properties compared to the nonfluorinated one (PZn–TPA). Moreover, their deeper highest occupied molecular orbital energy levels were beneficial for boosting open-circuit voltages, and their enhanced face-on stacking improved the hole transport properties. The L-PSC using PZn–2FTPA achieved the highest performance of 18.85%. Thus far, this result is one of the highest reported power conversion efficiencies among the...

Simple but exceptionally efficient 4-diphenylaminocarbazole host material, 4-DPACz, is presented and compared with its positional isomer, 1-DPACz. The shift of diphenylamino substituent from the 1-position to 4-position of carbazole resulted in an increase in the HOMO energy level as well as an increase in triplet energy level. Having a high triplet energy level (2.76 eV) and well-matched HOMO energy level (−5.61 eV), 4-DPACz showed reduced driving voltage and higher efficiencies for solution-processed green PhOLEDs compated to PVK as well as 1-DPACz. Maximum luminous, power, and external quantum efficiencies reaching to 47.9 cd A–1, 25.2 lm W–1, and 14.3%, respectively, were achieved with a device configuration of [ITO/PEDOT:PSS/4-DPACz:Ir(mppy)3/TPBi/CsF/Al]. Additional enhancement of efficiencies of 4-DPACz was verified when incorporating another dopant, Ir(Si-bppy)2(acac), resulting in 59.1 cd A–1, 29.5 lm W–1, and 15.8%. Furthermore, reduced efficiency roll-off was clearly observed for 4-DPACz compar...

Hole-transport materials are a crucial element influencing the efficiency, hysteresis, and stability of perovskite solar cells (PSCs). Current state-of-the-art hole-transport materials require additional oxidizing dopants to achieve sufficient hole-transport properties; however, these dopants are environmentally harmful while also deteriorating the stability of PSCs. The development of high-performance dopant-free hole-transport materials is an important goal in the field of PSCs. In this work, we developed novel conjugated small-molecule based dopant-free hole-transport materials for PSCs containing di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) as a core unit. These small molecule hole-transport materials achieved higher hole mobility and interfacial charge transfer rates than optimally doped spiro-OMeTAD, the current-state-of-the-art hole-transport material. A low-temperature PSC device using a dopant-free small molecule hole-transport material displayed a PCE of 18.09% with negligible hysteresis, higher than a device using doped spiro-OMeTAD (17.82%). Notably, the hydrophobic nature of our dopant-free small molecule hole-transport materials afforded excellent air-storage stability of low-temperature PSCs (81% retention after 33 days), whereas the doped spiro-OMeTAD based PSCs rapidly degraded under identical conditions (

High performance colloidal quantum dot (CQD) solar cells were developed by modifying ZnO electron accepting layers (EALs) using self-assembled monolayers (SAMs) of highly polar molecules. A high molecular dipole moment of −10.07D was achieved by conjugating a strong electron donor, julolidine, to an electron acceptor, a cyanoacetic acid unit, through a thiophene moiety. The energetic properties of ZnO EALs were manipulated with respect to the dipole moment of the modifying molecules. The built-in potential (Vbi) and internal electric field (Eint) of CQD solar cells could thereby be tuned. The power conversion efficiency (PCE) of the SAM modified devices was improved from 3.7% to 12.9% relative to the unmodified devices as a function of molecular dipole moments (from −5.13D to −10.07D). All figures-of-merit of solar cells were improved simultaneously by SAM modification due to enhanced Vbi, Eint, and charge collection efficiency. The PCE of the highly polar molecule modified devices reached 10.89% with a VOC of 0.689 V, whereas that of the unmodified devices was 9.65% with a VOC of 0.659 V. Notably, the remarkably low energy loss of 0.433 eV is achieved in the SAM modified devices.

We synthesized a novel wide bandgap polymer, PDTFBT, forming a weak donor (WD)-weak acceptor (WA) structure for use in organic photodetectors (OPDs) and organic solar cells (OSCs). The fluorination in the D unit and the alkoxy substitution in the A unit induced WD and WA properties, respectively. The WD-WA structure of PDTFBT effectively broadened the bandgap compared to typical D-A structures, and the S-F and S-O dipole-dipole interactions induces a highly planar backbone structure with excellent π-π stacking in the vertical direction. In OPDs, conformationally less disordered PDTFBT polymer retained the constant responsivity and significantly improved the detectivity of PDTFBT:PC71BM devices even with a thick active layer of 470 nm, contrary to the variation in the responsivity of P3HT:PC61BM devices depending on the thickness. In OSCs, the deep HOMO energy level (−5.57 eV) of PDTFBT led to high Voc of 0.92 V in PDTFBT:PC71BM devices, which was 0.3 eV higher than that of P3HT:PC61BM devices (0.62 V), resulting in 1.8-fold enhanced power conversion efficiency. We demonstrated that the WD-WA structure with S-F and S-O interactions is highly promising strategy to make wide bandgap polymers for organic photodetectors and for the bottom cell of tandem architecture.

We synthesized the conjugated polymers PT2OBT, PVT2OBT, and PFBT2OBT for use in organic photodetecting devices. An octyloxy benzothiadiazole (OBT) moiety was used as a weak electron-accepting building block in the polymer system to cause the dominant absorption in the green-light region via weakening the intramolecular charge transfer (ICT) interactions between adjacent electron-donating moieties. In particular, indirect X-ray detection using a scintillator requires a low leakage current; thus, we focused on designing a molecular structure that can enhance the detectivity. The difluorobenzene-incorporated PFBT2OBT polymer showed a strong edge-on orientation both in the pristine film and in the blend film; however, PT2OBT and PVT2OBT have no preferred molecular orientation in the blend film. In the edge-on structure, the alkyl side chains of PFBT2OBT align on the surface of the electrode, forming an insulating layer, which decreases the tunneling leakage current, whereas in the latter cases, the interface between the semiconducting polymer backbone and PC70BM can come into contact with the electrode, forming a pathway for the leakage current. Consequently, the PFBT2OBT:PC70BM devices showed promising detectivities of over 1013 Jones over a wide range of reverse biases of up to −2 V, resulting from their low dark current density of less than 2.3 × 10−9 A cm−2.

Stress tests were conducted in the carbody of the railroad car to check the structural strength of the body of the railroad car. The objective of this study was to evaluate safety of the carbody of a railroad car under the maximal strength. The carbody of rolling stock is a principal structure that supports major equipment of the underframe and the freight. Therefore, the strength evaluation of this structure is important. This study was carried out to analyze the structure of carbody and evaluate safety under maximum vertical load, compressive load, and torsional load. Accordingly, stress tests were conducted on the carbody to measure the stress on each of their parts. Before the load test, a structural-analysis program was used for the stress distribution analysis of the body structure.

The backbone composition of conjugated copolymers is of great importance in determining the conjugated structure and intermolecular assembly and in manipulating their optical, electrochemical, and electronic properties. However, limited attention has been directed at controlling the backbone composition of donor–acceptor (D–A) type low bandgap polymers. Herein, we developed a series of D–A random copolymers (P(BDTT-r-DPP)) composed of different compositions of electron-rich (D) thienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT) and electron-deficient (A) pyrrolo[3,4-c]pyrrole-1,4-dione (DPP). The optical and electrical properties of D–A random copolymers could be controlled by tuning the ratios of BDTT to DPP (4:1, 2:1, 1:1, 1:2, and 1:4) in the polymer backbone; an increase in BDTT resulted in increased absorption in the range of 400–600 nm and a lower-lying highest occupied molecular orbital energy level, while a higher proportion of DPP induced stronger absorption in the range of 700–900 nm. The...

Organic photovoltaic Cells (OPVs) have been considered to be a next-generation energy source to overcome exhaustion of resources. Currently, OPVs are developed based on two types of donor material with polymer and small molecule. Polymeric donor materials have shown better power conversion efficiency (PCE) than small molecular donor materials, since it's easy to control the morphology of photoactive film. However, the difficulty in synthetic reproducibility and purification of polymeric donor were main drawback to overcome. And then, recently small molecule donor materials have been overcome bad morphology of OPVs film by using appropriate alkyl substituents and relatively long conjugation system. In this study, we designed and synthesized D-A-D-A-D type small molecular donor materials containing alternatively linked benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) units. Also, we studied on the effect of photovoltaic performance of prepared small molecular D-A-D-A-D type donor with variation of thiophene links and with/without hexyl substituent. Our small molecular donors showed HOMO energy levels from -5.26 to -5.34 eV and optical bandgaps from 1.70 to 1.87 eV by CV (cyclic voltammetry) and UV/Vis spectroscopy, respectively. Finally, 3.4% of PCE can be obtained using a mixture of BDT(DPP)2-T2 and PCBM as an active layer with a Voc of 0.78 V, a Jsc of 9.72 mA/cm2, and a fill factor of 0.44 under 100 mW/cm2 AM 1.5G simulated light. We will discuss the performance of D-A-D-A-D type small molecular donor based OPVs with variation of both terminal substituents.

Small molecular donor, DTDCTB achieved a high power conversion efficiency (PCE) value of 6.6 ± 0.2% in vacuum-deposited planar mixed heterojunction (PMHJ) structure. However, the same material just recorded PCE of 0.34% in solution processed small molecule based bulk heterjunction (BHJ) organic photovoltaic cells. For the improvement of organic photovoltaic cells (OPVs), In this study, we designed and synthesized several D-A-A (donor-acceptor-acceptor) type molecular electron donating materials. Ditolylaminothienyl moiety as an electron donating group connected to 1,2,5-benzothiadiazole as a conjugated electron accepting unit, simultaneously with an electron accepting terminal group such as cyano alkyl acetate and N-alkyl rhodanine. The thermal, photophysical, and electrochemical properties of prepared small molecules were investigated by DSC, UV/Vis spectroscopy and Cyclic Voltametry, respectively. As a result, 0.89% of PCE can be obtained from OPV using a mixture of DTATBTER and PCBM as an active layer with a Voc of 0.87 V, a Jsc of 3.20 mA/cm2, and a fill factor of 31.9%.

Optimization and analysis of conjugated polymer side chains for high-performance organic photovoltaic cells (OPVs) reveal a critical relationship between the chemical structure of the side chains and photovoltaic properties of polymer-based bulk heterojunction OPVs. In particular, the impact of the alkyl side chain length on the pi-bridging (thienothiophene, TT) unit is considered by designing and synthesizing a series of benzodithiophene derivatives (BDT(T)) and thieno[3,2-b]thiophene-pi-bridged thieno[3,4-c]pyrrole-4,6(5H)-dione (ttTPD) alternating copolymers, PBDT(T)center dot(R-2)ttTPD, with alkyl chains of varying length on the TT unit. Using a combination of 2D X-ray diffraction, Raman spectroscopy, and electrical device characterization, it is elucidated in detail how these subtle changes to the chemical structure affect the molecular conformation, thin film molecular packing, blend film morphology, optoelectronic properties, and hence overall photo-voltaic performance. For copolymers employing both the alkoxy or alkylthienyl-substituted BDT motifs, it is found that octyl side chains on TT unit yield the maximum degree of molecular backbone coplanarity and result in the highest quality of molecular packing and optimized hole mobility. Inverted devices fabricated using this PBDTT-8ttTPD: polymer/[6,6]-phenyl-C-71-butylic acid methyl ester active layer show a maximum power conversion efficiency (PCE) of 8.7% with large area cells (0.64 cm(2)) maintaining a PCE of 7.5%.

Organic small molecule (SM) acceptors containing a perylene diimide (PDI) moiety, F2B-T2PDI and T2PDI are synthesized, and the effects of their molecular geometry on the performance of fullerene-free organic photovoltaic (OPV) devices are investigated. The SM acceptors possess a PDI–core–PDI structure in which the PDI wing is connected to conjugated core units. By incorporation of a 2,5-difluorobenzene (F2B) moiety within the core unit, the planarity of the conjugated core is enhanced and the energy levels of the SM acceptor are down-shifted. In terms of molecular geometry, the F2B-containing SM acceptor, F2B-T2PDI, has a rigid core, which can symmetrically align the two PDI wings and enhance molecular packing. As a result, improved electron transport and bulk heterojunction morphology of the active layers are achieved. Furthermore, the incorporation of the F2B moiety effectively down-shifts the HOMO energy level, preventing back-transfer of holes from the acceptor to the cathode and enhancing the absorption of complementary wavelengths of the donor polymer, PTB7-Th. Leveraged by the beneficial geometric and energetic effects from the incorporation of F2B units, the power conversion efficiency of fullerene-free OPV devices using F2B-T2PDI reached 5%, whereas that using T2PDI was 3.63%.

In this study, we explore the effects of alkylthiophene (T) and alkylthiothiophene (T-S) substituents on the benzo[1,2-b;4,5-b′]dithiophene (BDT) unit by comparing the BDTT homopolymer (PBDTT), the BDTT-alt-BDTT-S copolymer (PBDTT-BDTT-S), and the BDTT-S homopolymer (PBDTT-S) in terms of UV-visible absorption spectra, cyclic voltammetry (CV) results, computational calculations, and experimental results. The T-S substituent increased the hole mobility of the polymer and down-shifted the highest occupied molecular orbital (HOMO) energy level of the polymer, leading to slight red-shifting of the absorption spectrum. The organic photovoltaic (OPV) cells based on PBDTT-S as a donor and [6,6]-phenyl-C71-butylic acid methyl ester (PC71BM) as an acceptor demonstrated a high power conversion efficiency (PCE) of 7.05% under AM 1.5G illumination (100 mW cm−2). To the best of our knowledge, this PCE value is one of the highest values reported for homopolymer donor-based OPVs. Compared to the well-known P3HT homopolymer, which shows a similar absorption profile, PBDTT-S is a promising candidate for organic photodiodes.

We have synthesized a novel isoindigo-based electron donor polymer (PDBTPI) for organic photovoltaics. The alternating polymer comprising isoindigo and di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) moieties provides the highest power conversion efficiency of over 7% among DBTP-based polymers and a promising efficiency among isoindigo-based polymers.