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The matching of charge transport layer and photoactive layer is critical in solar energy conversion devices, especially for planar perovskite solar cells based on the SnO2 electron-transfer layer (ETL) owing to its unmatched photogenerated electron and hole extraction rates. Graphdiyne (GDY) with multi-roles has been incorporated to maximize the matching between SnO2 and perovskite regarding electron extraction rate optimization and interface engineering towards both perovskite crystallization process and subsequent photovoltaic service duration. The GDY doped SnO2 layer has fourfold improved electron mobility due to freshly formed C-O σ bond and more facilitated band alignment. The enhanced hydrophobicity inhibits heterogeneous perovskite nucleation, contributing to a high-quality film with diminished grain boundaries and lower defect density. Also, the interfacial passivation of Pb-I anti-site defects has been demonstrated via GDY introduction.

Phosphonium-based polythiophene conjugated polyelectrolytes (CPEs) with three different counterions (dodecylsulfate, octylsulfate and perfluorooctane sulfonate) are synthesized to determine how the nature of the counterion affects the thermal properties, the self-assembly in thin films and the performance as the cathode interfacial layer in polymer solar cells (PSCs). The counterion has a significant effect on the thermal properties of the CPEs, affecting both their glass transition and crystalline behaviour. Grazing-incidence wide-angle X-ray scattering studies also indicate that changing the nature of the counterion influences the microstructural organization in thin films (face-onversusedge-on orientation). The affinity of the CPEs with the underlying photoactive layer in PSCs is highly correlated with the counterion species. Finally, in addition to an increase of the power conversion efficiency ofca15% when using these CPEs as cathode interfacial layers in PSCs, a higher device stability is noted, compared to a reference device with a calcium interlayer. (c) 2020 Society of Industrial Chemistry This work was supported by the CNRS and the Universite de Montpellier. This work was also supported in part by the Science Foundation Ireland under grant no. 12/IP/1608. Research in Mons is supported by FNRS-FRFC (2Dto3D project - EOS programme) and Region Wallonne (OPTI2MAT excellence programme). The University of Mons and Hasselt University co-authors are grateful for financial support by the Science Policy Office of the Belgian Federal Government (BELSPO; PAI/IAP 7/05). JK is a postdoctoral fellow of the Research Foundation - Flanders (FWO Vlaanderen). NVdB thanks the Vrije Universiteit Brussel for a post-doctoral grant. The HINT COST action MP1202 and French-Irish programme 'Hubert Curien Ulysses' (31998ZF) are also acknowledged for support. This research has also been supported by the European Commission under the 7th Framework Programme through the 'Research Infrastructures' action of the 'Capacities' programme (contract no. CP-CSA_INFRA-2008-1.1.1 Number 226507-NM13). We further thank the Diamond Light Source for beamtime at the I07 beamline (experiment SI13868) and TA Instruments for the RHC equipment. Clement, S (corresponding author), Univ Montpellier, ENSCM, CNRS, ICGM, Montpellier, France. sebastien.clement1@umontpellier.fr

Achieving an ideal morphology is an imperative avenue for enhancing key parameters toward high‐performing organic solar cells (OSCs). Among a myriad of morphological‐control methods, the strategy of incorporating a third component with structural similarity and crystallinity difference to construct ternary OSCs has emerged as an effective approach to regulate morphology. A nematic liquid‐crystalline benzodithiophene terthiophene rhodamine (BTR) molecule, which possesses the same alkylthio‐thienyl‐substituted benzo moiety but obviously stronger crystallinity compared to classical medium‐bandgap polymeric donor PM6, is employed as a third component to construct ternary OSCs based on a PM6:BTR:Y6 system. The doping of BTR (5 wt%) is found to be enough to improve the OSC morphology—significantly enhancing the crystallinity of the photoactive layer while slightly reducing the donor/acceptor phase separation scale simultaneously. Rarely is such a morphology evolution reported. It positively affects the electronic properties of the device—prolongs the carrier lifetime, shortens the photocurrent decay time, facilitates exciton dissociation, charge transport, and collection, and ultimately boosts the power conversion efficiency from 15.7% to 16.6%. This result demonstrates that the successful synergy of liquid‐crystalline small‐molecule and polymeric donors delicately adjusts the active‐layer morphology and refines device performance, which brings vibrancy to the OSC research field., The nematic liquid‐crystalline small‐molecule donor benzodithiophene terthiophene rhodamine (BTR) works as a successful third component in PM6:Y6‐based organic solar cells. The doping of BTR significantly enhances the crystallinity with slightly reducing donor/acceptor phase separation of the photoactive layer. This uncommon morphology evolution facilitates charge separation, transport, and collection and ultimately boosts the efficiency from 15.7% to 16.6%.

The solution-processed solar cells based on colloidal quantum dots (QDs) reported so far generally suffer from poor thickness tolerance and it is difficult for them to be compatible with large-scale solution printing technology. However, the recently emerged perovskite QDs, with unique high defect tolerance, are particularly well-suited for efficient photovoltaics. Herein, efficient CsPbI3 perovskite QD solar cells are demonstrated first with over 1 µm-thick active layer by developing an internal P/N homojunction. Specifically, an organic dopant 2,2'-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6TCNNQ) is introduced into CsPbI3 QD arrays to prepare different carrier-type QD arrays. The detailed characterizations reveal successful charge-transfer doping of QDs and carrier-type transformation from n-type to p-type. Subsequently, the P/N homojunction perovskite QD solar cell is assembled using different carrier-type QDs, delivering an enhanced power conversion efficiency of 15.29%. Most importantly, this P/N homojunction strategy realizes remarkable thickness tolerance of QD solar cells, showing a record high efficiency of 12.28% for a 1.2 µm-thick QD active-layer and demonstrating great potential for the future printing manufacturing of QDs solar cells.

Despite more potential in realizing higher photovoltaic performance, the highest power conversion efficiency (PCE) of tandem organic photovoltaic (OPV) cells still lags behind that of state-of-the-art single-junction cells. In this work, highly efficient double-junction tandem OPV cells are fabricated by optimizing the photoactive layers with low voltage losses and developing an effective method to tune optical field distribution. The tandem OPV cells studied are structured as indium tin oxide (ITO)/ZnO/bottom photoactive layer/interconnecting layer (ICL)/top photoactive layer/MoOx /Ag, where the bottom and top photoactive layers are based on blends of PBDB-TF:ITCC and PBDB-TF:BTP-eC11, respectively, and ICL refers to interconnecting layer structured as MoOx /Ag/ZnO:PFN-Br. As these results indicate that there is not much room for optimizing the bottom photoactive layer, more effort is put into fine-tuning the top photoactive layer. By rationally modulating the composition and thickness of PBDB-TF:BTP-eC11 blend films, the 300 nm-thick PBDB-TF:BTP-eC11 film with 1:2 D/A ratio is found to be an ideal photoactive layer for the top sub-cell in terms of photovoltaic characteristics and light distribution control. For the optimized tandem cell, a PCE of 19.64% is realized, which is the highest result in the OPV field and certified as 19.50% by the National Institute of Metrology.

A series of novel highly soluble double-caged [60]fullerene derivatives were prepared by means of lithium-salt-assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four-membered cycle and a pyrrolizidine bridge with an ester function CO2 R (R=n-decyl, n-octadecyl, benzyl, and n-butyl; compounds 1 a-d, respectively), as demonstrated by NMR spectroscopy and X-ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one-electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone-electron pair. Owing to charge delocalization over both carbon cages, compounds 1 a-d are characterized by upshifted energies of frontier molecular orbitals, a narrowed bandgap, and reduced electron-transfer reorganization energy relative to pristine C60 . Neat thin films of the n-decyl compound 1 a demonstrated electron mobility of (1.3±0.4)×10-3 cm2 V-1 s-1 , which was comparable to phenyl-C61 -butyric acid methyl ester (PCBM) and thus potentially advantageous for organic solar cells (OSC). Application of 1 in OSC allowed a twofold increase in the power conversion efficiencies of as-cast poly(3-hexylthiophene-2,5-diyl) (P3HT)/1 devices relative to the as-cast P3HT/PCBM ones. This is attributed to the good solubility of 1 and their enhanced charge-transport properties - both intramolecular, owing to tightly linked fullerene cages, and intermolecular, owing to the large number of close contacts between the neighboring double-caged molecules. Test P3HT/1 OSCs demonstrated power-conversion efficiencies up to 2.6 % (1 a). Surprisingly low optimal content of double-caged fullerene acceptor 1 in the photoactive layer (≈30 wt %) favored better light harvesting and carrier transport owing to the greater content of P3HT and its higher degree of crystallinity.

Light harvesting (LH) and carrier transport abilities of a photoactive layer, which are both crucial for optoelectronic devices such as solar cells and photodetectors (PDs), are typically hard to be synergistically improved. Taking perovskite as an example, a freeze-drying recrystallization method is used to construct porous films with improvements of both LH and carrier transport ability. During the freeze-drying casting process, the rapid solvent evaporation produces massive pores, the sizes of which can be adjusted to exploit the Mie scattering for enhancement of the LH ability. Meanwhile, owing to the strong iconicity, the interface between perovskite nanocrystals fused during recrystallization, which favors carrier transport. Subsequently, PDs based on these Mie porous and interface-fused films show a high on/off ratio of more than 104 and an external quantum efficiency value of 658 % under 9 V bias and 520 nm light irradiation.

Two perylenediimides (PDIs), PT and PT2, functionalized with thiophene heterocycles on the 1,7-positions of the bay region were synthesized and utilized in inverted bulk-heterojunction (BHJ) polymer solar cells as acceptors in the photoactive layer. The synthesized PDIs were thermally stable up to 453°C and soluble in chlorinated solvents such as dichloromethane and chloroform. PT or PT2 was blended with poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]bithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PCE-10) as a donor material. The inverted BHJ solar cell fabricated using the PCE-10:PT photoactive layer showed the highest power conversion efficiency (PCE) of 2.06%. Film morphology studies of PCE-10:PDI blends revealed a relationship between the film nanostructure and device performance.

The search for greater efficiency in organic dye-sensitized solar cells (DSCs) and in their perovskite cousins is greatly aided by a more complete understanding of the spectral and morphological properties of the photoactive layer. This investigation resolves a discrepancy in the observed photoconversion efficiency (PCE) of two closely related DSCs based on carbazole-containing D-π-A organic sensitizers. Detailed theoretical characterization of the absorption spectra, dye adsorption on TiO2 , and electronic couplings for charge separation and recombination permit a systematic determination of the origin of the difference in PCE. Although the two dyes produce similar spectral features, ground- and excited-state density functional theory (DFT) simulations reveal that the dye with the bulkier donor group adsorbs more strongly to TiO2 , experiences limited π-π aggregation, and is more resistant to loss of excitation energy via charge recombination on the dye. The effects of conformational flexibility on absorption spectra and on the electronic coupling between the bright exciton and charge-transfer states are revealed to be substantial and are characterized through density-functional tight-binding (DFTB) molecular dynamics sampling. These simulations offer a mechanistic explanation for the superior open-circuit voltage and short-circuit current of the bulky-donor dye sensitizer and provide theoretical justification of an important design feature for the pursuit of greater photocurrent efficiency in DSCs. © 2017 Wiley Periodicals, Inc.

A green and facile method has been developed for the room temperature and aqueous solution preparation of NiOx film as anode buffer layers for polymer solar cells (PSCs). The NiOx buffer layer is prepared simply by spin-coating nickel acetylacetonate precursor-based aqueous solution onto ITO substrate at room temperature in air. UV-ozone post-treatment promotes the formation of dipolar NiOOH species on the film surface, resulting in the anode buffer layer with suitable work function. PSCs have been fabricated with the device structure of ITO/NiOx/photoactive layer/PFN/Al. The power conversion efficiencies of the PSCs based on PTB7:PC71BM blends (8.43%) and P3HT:PC71BM blends (3.04%) with NiOx anode buffer layer are comparable to those with the commonly used PEDOT:PSS anode buffer layer. In addition, the devices made with NiOx buffer layer exhibit much better air stability than those with PEDOT:PSS. These results indicate that the water solution processed NiOx film at room temperature in air is a promising anode buffer layer for efficient and stable PSCs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 747–753

Despite being widely used as electron acceptor in polymer solar cells, commercially available PC71BM (phenyl-C71-butyric acid methyl ester) usually has a "random" composition of mixed regioisomers or stereoisomers. Here the PC71BM has been isolated into three typical isomers, α-, β1- and β2-PC71BM, for establishing the isomer-dependent photovoltaic performance on change of ternary composition of α-, β1- and β2-PC71BM. Mixing the isomers in a ratio of α:β1:β2=8:1:1 resulted in the best power conversion efficiency (PCE) of 7.67% for the polymer solar cells with PTB7:PC71BM as photoactive layer (PTB7 = poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]). The three typical PC71BM isomers, even though sharing similar LUMO energy level and light absorption, render starkly different photovoltaic performances with average-performing PCE of 1.28-7.44% due to diverse self-aggregation of individual or mixed PC71BM isomers in the otherwise same polymer solar cells.

Photodetectors selective to the polarization empower breakthroughs in sensing technology for target identification. However, the realization of polarization-sensitive photodetectors based on intrinsically anisotropic crystal structure or extrinsically anisotropic device pattern requires complicated epitaxy and etching processes, which limit scalable production and application. Here, solution-processed PEA2 MA4 (Sn0.5 Pb0.5 )5 I16 (PEA= phenylethylammonium, MA= methylammonium) polycrystalline film is probed as photoactive layer toward sensing polarized photon from 300 to 1050 nm. The growth of the PEA2 MA4 (Sn0.5 Pb0.5 )5 I16 crystal occurs in confined crystallographic orientation of the (202) facet upon the assistance of NH4 SCN and NH4 Cl, enhancing anisotropic photoelectric properties. Therefore, the photodetector achieves a polarization ratio of 0.41 and dichroism ratio (Imax /Imin ) of 2.4 at 900 nm. At 520 nm, the Imax /Imin even surpasses the one of the perovskite crystalline films, 1.8 and ≈1.2, respectively. It is worth noting that the superior figure-of-merits possess a response width of 900 kHz, Ion /Ioff ratio of ≈3 × 108 , linear dynamic range from 0.15 nW to 12 mW, noise current of 8.28 × 10-13 A × Hz-0.5 , and specific detectivity of 1.53 × 1012 Jones, which demonstrate high resolution and high speed for weak signal sensing and imaging. The proof of concept in polarized imaging confirms that the polarization-sensitive photodetector meets the requirements for practical application in target recognition.

In this study, we report a new hole-collecting interlayer (HCI) comprising NiO/Au/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) for poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM)-based polymer solar cells (PSCs). The insertion of a bilayer of NiO/Au between indium tin oxide (ITO) and PEDOT:PSS improves the photocurrent generation of the PSCs. The NiO layer provides an intermediate step energy level between ITO and PEDOT:PSS, leading to enhanced hole collection. The ultrathin Au induces a surface plasmon resonance effect, allowing more photons to be absorbed by the photoactive layer and improving the hole-collecting properties by planarizing and doping the NiO. The PSCs with the NiO/Au/PEDOT:PSS HCIs yield a power-conversion efficiency of 3.9 ± 0.2%, which is approximately 15% higher than that of PSCs with a PEDOT:PSS-only HCI, under a simulated air mass 1.5 global (G) 100 mW/cm2 illumination.

Effective engineering of surface ligands in semiconductor nanocrystals can facilitate the electronic interaction between the individual nanocrystals, making them promising for low-cost optoelectronic applications. Here, the use of high purity Cu2ZnSnS4 (CZTS) nanocrystals as the photoactive layer and hole-transporting material is reported in low-temperature solution-processed solar cells. The high purity CZTS nanocrystals are prepared by engineering the surface ligands of CZTS nanocrystals, capped originally with the long-chain organic ligand oleylamine. After ligand removal, CZTS nanocrystals show substantial improvement in photoconductivity and mobility, displaying also an appreciable photoresponse in a simple heterojunction solar cell architecture. More notably, CZTS nanocrystals exhibit excellent hole-transporting properties as interface layer in perovskite solar cells, yielding power conversion efficiency (PCE) of 15.4% with excellent fill factor (FF) of 81%. These findings underscore the importance of removing undesired surface ligands in nanocrystalline optoelectronic devices, and demonstrate the great potential of CZTS nanocrystals as both active and passive material for the realization of low-cost efficient solar cells.

In this manuscript we reported the synthesis of diethynylbenzo[1,2-b:4,5-b′]dithiophene(DEBDT)-based small molecule BDTTIPS and three new cross-conjugated copolymers PBDTE-Th, PBDTE-FBT, and PBDTE-DPP that consist of DEBDT unit. The thermal, optophysical, and electronic properties of these materials were systematically investigated. The small molecule BDTTIPS exhibited higher absorption coefficient than the cross-conjugated copolymers. The LUMO/HOMO energy levels of such three cross-conjugated copolymers were −3.74/5.51, −3.77/–5.53, and −4.02/–5.58 eV as estimated from cyclic voltammetry measurements, which were lower than that of −3.63/–5.39 eV for the small molecule BDTTIPS. Due to the unique molecular structure and electronic properties of cross-conjugated polymers, hole mobilities of PBDTE-Th and PBDTE-DPP were higher than that of BDTTIPS. Photovoltaic performances were investigated by fabricating organic solar cells with the configuration of ITO/PEDOT:PSS/donor:PC61BM/Ca/Al. The small molecule chromophore BDTTIPS exhibited a power conversion efficiency of 4.19%, which was much higher than those obtained from devices based on conjugated polymers as the photoactive layer. These observations indicated that the DEBDT can be a promising building block for the construction of organic semiconducting materials for organic solar cell applications, and the rational molecular design was required for the attainment of high photovoltaic performances. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016

A novel wide-bandgap conjugated polymer PBTA-FPh based on benzodithiophene-alt-benzo[1,2,3]triazole as the main chain and a polar pentafluorothiophenyl (FPh) group in the side chain has been designed and synthesized. In comparison to the pristine polymer PBTA-BO that consists of nonpolar alkyl side chains, the resulting PBTA-FPh exhibits less pronounced aggregation while possessing analogous optical and electrochemical bandgaps. Contact angle measurements demonstrate that the surface energy can be enhanced by incorporating FPh moiety, leading to a better miscibility of PBTA-BO with PC71BM in the presence of a certain amount of PBTA-FPh. The photoactive layer of PBTA-BO:PC71BM:PBTA-FPh with weight ratio of 1:1.2:0.02% exhibits a percolated network with the fibrous features, as revealed by transmission electron microscopy measurements. Of particular interest is the significantly improved photovoltaic performances of polymer solar cell devices for which the power conversion efficiency is enhanced from 6.46% for the control device to 7.91% for device processed with PBTA-FPh as the polymeric additive. These observations indicate that introducing donor–acceptor type of polymeric additive comprising of polar groups in the side chain can be a promising strategy for the fabrication of high-performance polymer solar cells.

Visible-near infrared photodetectors are reported with excellent overall device parameters from conjugated polymers with different optical bandgaps by optimal design in device structure and optimizing the thickness of the photoactive layer in nanoscale. The best visible-near infrared photodetectors show high detectivity (D*) of 1.7 × 10(13) Jones at a wavelength of 710 nm, which is among one of the best results of polymer photodetectors reported to date.

The morphological quality of the photoactive layer is the key component affecting the performance metrics of a photovoltaic device. Therefore, fine adjustment of the crystallization dynamics is urgently required. By manipulating the amount of dimethyl sulfoxide (DMSO) remaining in the spin-coated perovskite films during the annealing treatment, an obvious morphological evolution arises. The crystallization kinetics is significantly altered due to the formation of intermediate phases and the variation of DMSO vapor pressure via producing the semienclosed space with a covering. On the one hand, the obviously formed intermediate phase MA2 Pb3 I8 (DMSO)2 retards the crystallization process. On the other hand, the DMSO vapor in the semienclosed space intrigues the recrystallization process and results in Ostwald ripening to produce large-aspect-ratio grains with fewer defect states, decreased carrier doping, and longer carrier lifetimes. Thus, nonradiative processes are greatly suppressed. Besides, combined with X-ray photoelectron spectroscopy measurement and the surface energy of MAI- and PbI-terminated surface model calculated by density functional theory, the defect states are identified and the causes of Pb0 defect states are explained. Using this strategy, a high power conversion efficiency of 20.09% is achieved based on MAPbI3 photovoltaic solar cell, and the long-term ambient shelf and thermal stability are obviously improved.

All-inorganic CsPbI3 holds promise for efficient tandem solar cells, but reported fabrication techniques are not transferrable to scalable manufacturing methods. Herein, printable CsPbI3 solar cells are reported, in which the charge transporting layers and photoactive layer are deposited by fast blade-coating at a low temperature (≤100 °C) in ambient conditions. High-quality CsPbI3 films are grown via introducing a low concentration of the multifunctional molecular additive Zn(C6 F5 )2 , which reconciles the conflict between air-flow-assisted fast drying and low-quality film including energy misalignment and trap formation. Material analysis reveals a preferential accumulation of the additive close to the perovskite/SnO2 interface and strong chemisorption on the perovskite surface, which leads to the formation of energy gradients and suppressed trap formation within the perovskite film, as well as a 150 meV improvement of the energetic alignment at the perovskite/SnO2 interface. The combined benefits translate into significant enhancement of the power conversion efficiency to 19% for printable solar cells. The devices without encapsulation degrade only by ≈2% after 700 h in air conditions.

Various approaches of interface engineering are shown to be effective in improving the device performance of organic–inorganic hybrid perovskite solar cells (PSCs). The modification of the photoactive layer of PSC, CH 3 NH 3 PbI 3 (MAPbI 3 ), by spin-coating a layer of p-aminobenzoic acid (PABA), which can significantly enhance the open-circuit voltage (V OC ), the fill factor (FF), and the power conversion efficiency (PCE) of PSCs, is herein reported. The champion device shows a short-circuit current (J SC ) of 22.83 mA cm−2, V OC of 1.167 V, FF of 0.768, and PCE of 20.47%. The improvement in photovoltaic performance is attributed to the suppression of carrier trap states and the improvement in the morphologies of perovskite films. This work demonstrates a simple and effective protocol to enhance the device performance, and provides an insight into the influence of PABA post-treatment on the charge carrier dynamics. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A dynamic-cooling and freeze-drying (DCFD) process has been applied to the fabrication of polymer solar cells. The dynamic-cooling process allows poly(3-hexylthiophene) molecules to aggregate in solution into a more organized structure during the cooling process; the freeze-drying process prevents severe agglomeration of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) during the solvent removing process. Application of these two processes to the preparation of the poly(3-hexylthiophene)/methanofullerene photoactive layer results in an enhanced poly(3-hexylthiophene) aggregation and smaller PCBM agglomerates. Devices fabricated using the DCFD process generate 14% more in current density than those prepared by the spin-coating process under AM1.5G illumination. © 2015 Society of Chemical Industry

Flexible semi-transparent organic photovoltaic (OPV) modules were manufactured by roll-to-roll slot–die coating of three functional layers [ZnO, photoactive layer, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)] and either the screen printing or inkjet printing of the top electrodes. A poly(3-hexylthiophene):[6,6] phenyl C61-butyric acid methyl ester (P3HT:PCBM) layer deposited from non-chlorinated solvents was used as the absorber layer. The modules were realized by slot–die coating of the layers onto a laser-patterned polyethylene terephthalate/indium-tin oxide (PET/ITO) substrate, followed by laser structuring of all coated layers. The top electrodes were realized by high-resolution printing, which, combined with laser patterning of other layers, enables manufacturing of the modules with high geometrical fill factor (92.5%). The modules have an active area of 156 cm2, and contain 13 serially interconnected cells. Two semitransparent electrodes (ITO from the bottom and PEDOT:PSS/Ag-grid from the top side) allow the absorption of photons incident from both sides. The performance of the modules was evaluated and compared among the modules by considering the following factors: (i) roll-to-roll slot–die coated vs. spin-coated layers,(ii) inkjet-printed vs. screen-printed top electrodes, (iii) top vs. bottom illumination. The demonstrated technology is one of the proven feasible ways towards industrial manufacturing of the OPV modules.

In the quest for indium-tin oxide (ITO)-free photovoltaics and for building integrated as well as automobile roof applications, novel transparent electrodes for both front and back electrodes are required. Here we report the fabrication and integration of submicrometer transparent silver (Ag) and gold (Au) metal network electrodes, which are invisible to the naked eye, in organic photovoltaic devices. We exploit the idea of using the spontaneous cracking of a polymer layer as template to prepare the metal network. The main challenge is to apply the cracked template approach on top of soluble organic layers and to lift off the template without damaging the photoactive layer. We demonstrate that Ag or Au back electrodes can be fabricated maintaining a transmittance of 80 % for the whole visible range. These electrodes exhibit ultralow haze of approximately 5 % and an excellent figure of merit value. Moreover, the ITO-free semitransparent polymer solar cell incorporating the Ag/Ag network electrodes exhibits 57 % transmittance above 650 nm.

A series of tetrafluorine-substituted small molecules with a D1-A-D2-A-D1 linear framework based on indacenodithiophene and difluorobenzothiadiazole is designed and synthesized for application as donor materials in solution-processed small-molecule organic solar cells. The impacts of thiophene π-bridge and multiple fluorinated modules on the photophysical properties, the energy levels of the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO), charge carrier mobility, the morphologies of blend films, and their photovoltaic properties as electron donor material in the photoactive layer are investigated. By incorporating multiple fluorine substituents of benzothiadiazole and inserting two thiophene spacers, the fill factor (FF), open-circuit voltage, and short-circuit current density are dramatically improved in comparison with fluorinated-free materials. With the solvent vapor annealing treatment, further enhancement in charge carrier mobility and power conversion efficiency (PCE) are achieved. Finally, a high PCE of 8.1% with very-high FF of 0.76 for BIT-4F-T/PC71BM is achieved without additional additive, which is among one of the highest reported for small-molecules-based solar cells with PCE over 8%. The results reported here clearly indicate that high PCE in solar cells based small molecules can be significantly increased through careful engineering of the molecular structure and optimization on the morphology of blend films by solvent vapor annealing.

The exciton dynamics in pristine films of two structurally related low-bandgap diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers and the photophysical processes in bulk heterojunction solar cells using DPP copolymer:PC71 BM blends are investigated by broadband transient absorption (TA) pump-probe experiments covering the vis-near-infrared spectral and fs-μs dynamic range. The experiments reveal surprisingly short exciton lifetimes in the pristine poly-mer films in conjunction with fast triplet state formation. An in-depth analysis of the TA data by multivariate curve resolution analysis shows that in blends with fullerene as acceptor ultrafast exciton dissociation creates charge carriers, which then rapidly recombine on the sub-ns timescale. Furthermore, at the carrier densities created by pulsed laser excitation the charge carrier recombination leads to a substantial population of the polymer triplet state. In fact, virtually quantitative formation of triplet states is observed on the sub-ns timescale. However, the quantitative triplet formation on the sub-ns timescale is not in line with the power conversion efficiencies of devices indicating that triplet state formation is an intensity-dependent process in these blends and is reduced under solar illumination conditions, as free charge carriers can be extracted from the photoactive layer in devices.

The experimental current is scaled by the generat o transportation (Ind recomhination loss of the mohile carriers. In this paper. We show that a change ol small molecule/ perylene diimide (PDI) weight ratio from I:I to 3:1 does not lead to different transportation or different recombination loss in the solar cell. while it results in different ge en at ion of the mohi le carriers. With the increase of the donor/acceptor (D/A) ratio. the blend film has an enhanced absorption because the donor has a stronger light-harvesting ahility than the P1 acceptor. With respect to the contrihution from the enhancement of the absorption of the solar photons. our data demonstrate that the phase site of the acceptor Holton domains is the key factor that determines the generation of the mobile carriers. We observe a good relationship between the average short-circuit current density (m 1 and phase site of the acceptor domains. Through line-tuning the D/A ratio. the hest compatihility hemeen the small molecule donor and the PD1 acceptor is ohtained at a mediate D/A ratio of 1.3:1. at which the absorbed solar photons are exploited el hciently. yielding an average power conversion efficiency of over Compatihility and charge sep(tration are modulated hy Vary i ng donor weight ration in small molecule donorperylene diimide hased non-fullerene solar cells. NVI1 al101dS improved exploitation of the solar photons absorbed by the photoactive layer. The acceptor phase site is a Rey Iactor that scales the photocurrent. An efficiency of 5.1 is ohtained from this non-fullerene small molecule system as a result of modulation of compatibility. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Organic photovoltaics (OPVs) have been pursued as a next generation power source due to their light weight, thin, flexible, and simple fabrication advantages. Improvements in OPV efficiency have attracted great attention in the past decade. Because the functional layers in OPVs can be dissolved in common solvents, they can be manufactured by eco-friendly and scalable printing or coating technologies. In this review article, the focus is on recent efforts to control nanomorphologies of photoactive layer and discussion of various solution-processed charge transport and extraction materials, to maximize the performance of OPV cells. Next, recent works on printing and coating technologies for OPVs to realize solution processing are reviewed. The review concludes with a discussion of recent advances in the development of non-traditional lamination and transfer method towards highly efficient and fully solution-processed OPV.

In this work, a high-performance ITO-free flexible polymer solar cell (PSC) is successfully described by integrating the plasmonic effect into the ITO-free microcavity architecture. By carefully controlling the sizes of embedded Ag nanoprisms and their doping positons in the stratified device, a significant enhancement in power conversion efficiency (PCE) is shown from 8.5% (reference microcavity architecture) to 9.4% on flexible substrates. The well-manipulated plasmonic resonances introduced by the embedded Ag nanoprisms with different LSPR peaks allow the complementary light-harvesting with microcavity resonance in the regions of 400–500 nm and 600–700 nm, resulting in the substantially increased photocurrent. This result not only signifies that the spectral matching between the LSPR peaks of Ag nanoprisms and the relatively low absorption response of photoactive layer in the microcavity architecture is an effective strategy to enhance light-harvesting across its absorption region, but also demonstrates the promise of tailoring two different resonance bands in a synergistic manner at desired wavelength region to enhance the efficiency of PSCs.

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The π-conjugated organic small molecule 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl) benzenamine] (TAPC) has been explored as an efficient hole transport material to replace poly(3,4-ethylenedio-xythiophene):poly(styrenesulfonate) (PEDOT:PSS) in the preparation of p-i-n type CH 3 NH 3 PbI 3 perovskite solar cells. Smooth, uniform, and hydrophobic TAPC hole transport layers can be facilely deposited through solution casting without the need for any dopants. The power conversion efficiency of perovskite solar cells shows very weak TAPC layer thickness dependence across the range from 5 to 90 nm. Thermal annealing enables improved hole conductivity and efficient charge transport through an increase in TAPC crystallinity. The perovskite photoactive layer cast onto thermally annealed TAPC displays large grains and low residual PbI 2 , leading to a high charge recombination resistance. After optimization, a stabilized power conversion efficiency of 18.80% is achieved with marginal hysteresis, much higher than the value of 12.90% achieved using PEDOT:PSS. The TAPC-based devices also demonstrate superior stability compared with the PEDOT:PSS-based devices when stored in ambient circumstances, with a relatively high humidity ranging from 50 to 85%.

Semiconductor organic-inorganic nanocomposites have garnered much attention as they integrate the advantageous properties from conjugated polymers (CPs) and semiconductor nanocrystals (NCs). Recent developments in interfacial engineering of CP-NC nanocomposites enabled the intimate contact between CPs and NCs, thereby facilitating charge separation between these two constituents. To capitalize on the use of CP-NC nanocomposites for hybrid solar cells, several issues need to be addressed, including materials design and engineering, light harvesting, and morphology of photoactive layer. In this Review, the general working principle of hybrid solar cells and the development of p-type and n-type CPs are briefly introduced, followed by the highlight of recent advances in synthesis of CP-NC nanocomposites in which CP and NC are in intimate contact for hybrid solar cells, and the discussion on various strategies for potentially improved power conversion efficiency. An outlook for future directions in this area is also presented. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1641–1660

A new donor-acceptor conjugated copolymer (PDTPyDPP), comprising 2,7-di-2-thienyl-4,5,9,10-tetrakis(hexyloxy)pyrene as a donor and diketopyrrolopyrrole (DPP) as an acceptor, was synthesized. PDTPyDPP showed good solubility in common organic solvents, broad visible absorption from 300 to 900 nm, and a moderate hole mobility up to 6.3 x 10(-3) cm(2) V-1 s(-1). The power conversion efficiency of the photovoltaic device based on the PDTPyDPP/PC71BM photoactive layer reached 4.43% with 0.66 V of open-circuit voltage (V-oc), 10.52 mA cm(-2) of short-circuit current (J(sc)) and 64.11% of fill factor. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3198-3204

Inverted-type bulk-heterojunction organic thin-film solar cells with incorporated gold nanoparticles were fabricated and evaluated. Gold nanoparticles were incorporated into the hole-transport layer, and subsequently positioned behind the photoactive layer, away from the light-facing side of the solar cell. Incorporation of gold nanoparticles was confirmed by scanning electro microscopy, atomic force microscopy, and transmission absorption spectra. The incorporation of the gold nanoparticles improved the performance of the photovoltaic device, even gold nanoparticles were aggregated in the hole-transport layer.

Two-dimensional graphene-CdS (G-CdS) semiconductor hybrid nanosheets were synthesized in situ by graphene oxide (GO) quantum wells and a metal-xanthate precursor through a one-step growth process. Incorporation of G-CdS nanosheets into a photoactive film consisting of poly[4,8-bis-(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b]dithiophene-2,6-diyl]-alt-[2-(2-ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl] (PBDTTT-C-T) and [6,6]-phenyl C70 butyric acid methyl ester (PC70 BM) effectively decreases the exciton lifetime to accelerate exciton dissociation. More importantly, the decreasing energy levels of PBDTTT-C-T, PC70 BM, and G-CdS produces versatile heterojunction interfaces of PBDTTT-C-T:PC70 BM, PBDTTT-C-T:G-CdS, and PBDTTT-C-T:PC70 BM:G-CdS; this offers multi-charge-transfer channels for more efficient charge separation and transfer. The charge transfer in the blend film also depends on the G-CdS nanosheet loadings. In addition, G-CdS nanosheets improve light utilization and charge mobility in the photoactive layer. As a result, by incorporation of G-CdS nanosheets into the active layer, the power-conversion efficiency of inverted solar cells based on PBDTTT-C-T and PC71 BM is improved from 6.0 % for a reference device without G-CdS nanosheets to 7.5 % for the device with 1.5wt % G-CdS nanosheets, due to the dramatically enhanced short-circuit current. Combined with the advantageous mechanical properties of the PBDTTT-C-T:PC70 BM:G-CdS active layer, the novel CdS-cluster-decorated graphene hybrid nanomaterials provide a promising approach to improve the device performance.

Although rapid progress has been made recently in bulk heterojunction organic solar cells, systematic studies on an ultrathin interfacial layer at the electron extraction contact have not been conducted in detail, which is important to improve both the device efficiency and the lifetime. We find that an ultrathin BaF2 layer at the electron extraction contact strongly influences the open-circuit voltage (Voc ) as the nanomorphology evolves with increasing BaF2 thickness. A vacuum-deposited ultrathin BaF2 layer grows by island growth, so BaF2 layers with a nominal thickness less than that of single-coverage layer (≈3 nm) partially cover the polymeric photoactive layer. As the nominal thickness of the BaF2 layer increased to that of a single-coverage layer, the Voc and power conversion efficiency (PCE) of the organic photovoltaic cells (OPVs) increased but the short-circuit current remained almost constant. The fill factor and the PCE decreased abruptly as the thickness of the BaF2 layer exceeded that of a single-coverage layer, which was ascribed to the insulating nature of BaF2 . We find the major cause of the increased Voc observed in these devices is the lowered work function of the cathode caused by the reaction and release of Ba from thin BaF2 films upon deposition of Al. The OPV device with the BaF2 layer showed a slightly improved maximum PCE (4.0 %) and a greatly (approximately nine times) increased device half-life under continuous simulated solar irradiation at 100 mW cm(-2) as compared with the OPV without an interfacial layer (PCE=2.1 %). We found that the photodegradation of the photoactive layer was not a major cause of the OPV degradation. The hugely improved lifetime with cathode interface modification suggests a significant role of the cathode interfacial layer that can help to prolong device lifetimes.

Lead-(Pb-) halide perovskite nanocrystals (NCs) are interesting nanomaterials due to their excellent optical properties, such as narrow-band emission, high photoluminescence (PL) efficiency, and wide color gamut. However, these NCs have several critical problems, such as the high toxicity of Pb, its tendency to accumulate in the human body, and phase instability. Although Pb-free metal (Bi, Sn, etc.) halide perovskite NCs have recently been reported as possible alternatives, they exhibit poor optical and electrical properties as well as abundant intrinsic defect sites. For the first time, the synthesis and optical characterization of cesium ytterbium triiodide (CsYbI3 ) cubic perovskite NCs with highly uniform size distribution and high crystallinity using a simple hot-injection method are reported. Strong excitation-independent emission and high quantum yields for the prepared NCs are verified using photoluminescence measurements. Furthermore, these CsYbI3 NCs exhibit potential for use in organic-inorganic hybrid photodetectors as a photoactive layer. The as-prepared samples exhibit clear on-off switching behavior as well as high photoresponsivity (2.4 × 103 A W-1 ) and external quantum efficiency (EQE, 5.8 × 105 %) due to effective exciton dissociation and charge transport. These results suggest that CsYbI3 NCs offer tremendous opportunities in electronic and optoelectronic applications, such as chemical sensors, light emitting diodes (LEDs), and energy conversion and storage devices.

Photovoltaic devices employing lead halide perovskites as the photoactive layer have attracted enormous attention due to their commercialization potential. Yet, there exists challenges on the way to the practical use of perovskite solar cells (PSCs), such as light stability and current–voltage (J–V ) hysteresis. Inorganic perovskite nanocrystals (IPNCs) are promising candidates for high‐performance photovoltaic devices due to their simple synthesis methods, tunable bandgap, and efficient photon downshifting effect for ultraviolet (UV) light blocking and conversion. In this work, CsPbBr3 IPNCs modification could give rise to the vapor phase and solution‐processed PSCs with a power conversion efficiency (PCE) of 16.4% and 20.8%, respectively, increased by 11.6% and 5.6% compared to the control devices for more efficient UV utilization and carrier recombination suppression. As far as is known, 11.6% is the most effective enhanced factor for PSCs based on photon downshifting effect inside of devices. The CsPbBr3 layer could also significantly retard light‐induced degradation, leading to the lifetime over 100 h under UV illumination for PSCs. Additionally, the modified PSCs exhibit weak hysteresis and multiple colors of fluorescence. These results shed light on the future design of combining a photon downshifting layer and carrier interfacial modification layer in the applications of perovskite optoelectronic devices.

A facile route to soft matter self-powered bulk heterojunction photodiode detectors sensitive to the circular polarization state of light is shown based on the intrinsic excitonic circular dichroism of the photoactive layer blend. As light detecting materials, enantiopure semiconducting small molecular squaraine derivates of opposite handedness are employed. Via Mueller matrix ellipsometry, the circular dichroism is proven to be of H-type excitonic nature and not originating from mesoscopic structural ordering. Within the green spectral range, the photodiodes convert circular polarized light into a handedness-dependent photocurrent with a maximum dissymmetry factor of ±0.1 corresponding to 5% overall efficiency for the polarization discrimination under short circuit conditions. On the basis of transfer matrix optical simulations, it is rationalized that the optical dissymmetry fully translates into a photocurrent dissymmetry for ease of device design. Thereby, the photodiode's ability to efficiently distinguish between left and right circularly polarized light without the use of external optical elements and voltage bias is demonstrated. This allows a straightforward and sustainable future design of flexible, lightweight, and compact integrated platforms for chiroptical imaging and sensing.

The interfacial charge effect is crucial for high-sensitivity organic phototransistors (OPTs), but conventional layered and hybrid OPTs have a trade-off in balancing the separation, transport, and recombination of photogenerated charges, consequently impacting the device performance. Herein, a novel hybrid-layered phototransistor (HL-OPT) is reported with significantly improved photodetection performance, which takes advantages of both the charge-trapping effect (CTE) and efficient carrier transport. The HL-OPT consisting of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as conduction channel, C8-BTBT:[6,6]-phenyl-C61 -butyric acid methyl ester (PC61 BM) bulk heterojunction as photoactive layer, and sandwiched MoO3 interlayer as a charge-transport interlayer exhibits outstanding photodetection characteristics such as a photosensitivity (Ilight /Idark ) of 2.9 × 106 , photoresponsivity (R) of 8.6 × 103 A W-1 , detectivity (D*) of 3.4 × 1014 Jones, and external quantum efficiency of 3 × 106 % under weak light illumination of 32 µW cm-2 . The mechanism and strategy described here provide new insights into the design and optimization of high-performance OPTs spanning the ultraviolet and near infrared (NIR) range as well as fundamental issues pertaining to the electronic and photonic properties of the devices.

Neutral-colored semitransparent organic solar cells (ST-OSCs) have attracted considerable attention owing to their unique application in no-visual-obstacle building-integrated photovoltaics. Toward this promising potential application, a synergistic effect is first proposed by employing a dielectric mirror and ternary photoactive layer with near-infrared absorption to tune the color perception as well as ST-OSC performance precisely. As a result, a neutral-color ST-OSC with high average transmittance of over 21% is successfully constructed, and a remarkable color-rendering index approaching 100 and high power conversion efficiency (PCE) of 9.37% are simultaneously achieved. To the best of our knowledge, this is the highest PCE reported for neutral-color ST-OSCs to date. Importantly, this synergistic effect is demonstrated to be a universal strategy that is not only suitable for various photoactive layer systems, but can also be implanted in flexible substrate. The resulting neutral-color flexible ST-OSCs also show a promising PCE of 8.76%.

Two novel anionic conjugated copolyelectrolytes PSDPPPV and PSDPPPE were synthesized via Heck/Sonogashira coupling reactions and characterized by FT-IR, 1H NMR, UV-vis, and PL spectroscopy. The two polymers are respectively constituted of 2,5-diethoxy-1,4-phenyleneethynylene (DPV) and 2,5-diethoxy-1,4-phenyleneethynylene (DPE) with 1,4-diketo-2,5-bis(4-sulfonylbutyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole (SDPP) which is a novel water soluble diketopyrrolopyrrole derivative. PSDPPPV and PSDPPPE show broad absorption band in visible region and they exhibit strong fluorescence quenching in aqueous solution. The fluorescence of their aqueous solutions can be enhanced in the presence of cationic surfactant or polymer nonionic surfactant. Fluorescence enhancement by introduction of polyvinylpyrrolidone (PVP) shows linear response. This result provides a controllable method to increase fluorescence intensity of dipyrrolopyrrole-based conjugate polyelectrolytes in aqueous phase. The optical properties suggested that PSDPPPV and PSDPPPE which are negatively charged conjugated polymers can assemble with positively charged photovoltaic materials to form ionic photoactive layer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 739–751

Top-illuminated flexible polymer solar cells with 3D micoresonant cavity provide not only powerful light-trapping but also electrical enhancement, resulting in significant enhancement of power efficiency (26.4%). Capping layer (CL) enhanced the transmittance of the transparent electrodes, increasing electric field intensity in the photoactive layer by forming microresonant cavity, and the nano-pattern on the rear electrodes caused significant enhancement to the Jsc by improving light absorption and charge collection.

Bulk heterojunction solar cells containing molybdenum oxide hole extracting anode contacts have been fabricated with varying stoicheometry using radio frequency reactive sputtering from a Molybdenum metal target. A blend of the newly synthesised conjugated polymer poly[9-(heptadecan-9-yl)-9H-carbazole-2,7-diyl-alt-(5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)-5,5-diyl] (PCDTBT-8) and fullerene [6,6]-Phenyl-C71-butyric acid methyl ester (PC70BM) was used as the photoactive layer and device results show that anodes with greater than 98% Molybdenum (VI) oxide result in peak power conversion efficiencies of 3.7%.The presence of up to 28% of Mo (V) results in no significant reduction in efficiency, however the presence of metallic Mo (IV) and lower oxidation states lead to severe reductions in device performance due to a combination of a large hole extraction energy barrier of approximately 0.9eV and reduced device stability.

We report the fabrication of high performance organic solar cells by spray-coating the photoactive layer in air. The photovoltaic blends consist of a blend of carbazole and benzothiadiazole based donor–acceptor copolymers and the fullerene derivative PC70BM. Here, we formulate a number of photovoltaic inks using a range of solvent systems that we show can all be deposited by spray casting. We use a range of techniques to characterize the structure of such films, and show that spray-cast films have comparable surface roughness to spin-cast films and that vertical stratification that occurs during film drying reduces the concentration of PCBM towards the underlying PEDOT:PSS interface. We also show that the active layer thickness and the drying kinetics can be tuned through control of the substrate temperature. High power conversion efficiencies of 4.3%, 4.5% and 4.6% were obtained for solar cells made from a blend of PC70BM with the carbazole-based co-polymers PCDTBT, P2 and P1. By applying a low temperature anneal after the deposition of the cathode, the efficiency of spray-cast solar-cells based on a P2:PC70BM blend is increased to 5.0%. Spray coating holds significant promise as a technique capable of fabricating large-area, high performance organic solar cells in air.

The detailed characterization of solution-derived nickel (II) oxide (NiO) hole-transporting layer (HTL) films and their application in high efficiency organic photovoltaic (OPV) cells is reported. The NiO precursor solution is examined in situ to determine the chemical species present. Coordination complexes of monoethanolamine (MEA) with Ni in ethanol thermally decompose to form non-stoichiometric NiO. Specifically, the [Ni(MEA)2(OAc)]+ ion is found to be the most prevalent species in the precursor solution. The defect-induced Ni3+ ion, which is present in non-stoichiometric NiO and signifies the p-type conduction of NiO, as well as the dipolar nickel oxyhydroxide (NiOOH) species are confirmed using X-ray photoelectron spectroscopy. Bulk heterojunction (BHJ) solar cells with a polymer/fullerene photoactive layer blend composed of poly-dithienogermole-thienopyrrolodione (pDTG-TPD) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are fabricated using these solution-processed NiO films. The resulting devices show an average power conversion efficiency (PCE) of 7.8%, which is a 15% improvement over devices utilizing a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. The enhancement is due to the optical resonance in the solar cell and the hydrophobicity of NiO, which promotes a more homogeneous donor/acceptor morphology in the active layer at the NiO/BHJ interface. Finally, devices incorporating NiO as a HTL are more stable in air than devices using PEDOT:PSS.