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SUMMARYRuddlesden-Popper (RP) perovskites are two-dimensional semiconductors for high performance devices. In this work, we report a long in-plane charge carrier diffusion length in 2D RP perovskite single crystals probed by scanning photocurrent microscopy. Carrier diffusion lengths of 7~14 µm are observed when the number of PbI6-2 octahedrons between organic spacers increases from 1 to 3. By detailed light intensity and electric field-dependent photocurrent measurements, we attribute the observed long diffusion length to the dominating dissociated free carrier transport. This is further validated by time-resolved photoluminescence measurements where the decay lifetime increases in the presence of an electric field. From our experiments, we conclude that the in-plane transport in RP perovskites is efficient because of the partial free carrier generation overcoming strong excitonic effects. Our results suggest that semiconducting devices fabricated from RP perovskite single crystals can be as efficient as their 3D counterparts.

Summary The one-step antisolvent approach is a widely employed method for fabricating perovskite devices at a low cost. However, the current antisolvent approach requires a strict set of processing conditions to obtain high-quality perovskite layers. Here, we introduce sulfolane as an additive in the perovskite precursor to convert the perovskite phase via a new reaction route, providing a large degree of flexibility to process crystalline perovskite layers with high uniformity on a large scale. As it is revealed by X-ray diffraction and Fourier-transform infrared spectroscopy findings, we find that the key concept lies in intermolecular hydrogen-bonding forces’ interaction between sulfolane and methylammonium iodide, which slows down the nucleation and subsequently the crystallization process. As a result, we demonstrate a mini module, 36.6 cm2 active area, and achieve a record PCE of 16.06%. More importantly, the encapsulated mini module retained about 90% of the initial performance after operating at the maximum power point under simulated AM1.5G irradiation for 250 h at 50°C.

A new donor–acceptor-type all-conjugated block copolymer (BCP), P(NDI-DBDT)-block-P(NDI-2T), is synthesized through the coupling of a naphthalene diimide (NDI)-bithiophene (2T) segment-based polymer (P1) and an NDI-dithienylbenzodithiophene (DBDT) segment-based polymer (P2). P1 has a prevailing backbone for NDI-based polymer acceptors, while P2 is modified to contain a p-type DBDT moiety to facilitate miscibility with the DBDT-based polymer donors. When adding 1 wt% BCP (the optimized blending amount) into the PBDB-T:N2200 blend that possesses similar constituent units to the BCP, the derived device can deliver an enhanced power conversion efficiency (PCE) of 7.07%, outperforming the control device (with a PCE of 5.71%). This improvement is found to arise from the more optimized bulk-heterojunction (BHJ) morphology as a result of facilitated intermixing between the photoactive components. This leads to reduced charge recombination and potential loss for the device. Moreover, the more optimized BHJ morphology endows the device with improved thermal robustness. It demonstrates longer T80 lifetimes when stored under constant thermal conditions at high temperatures. Consequently, the device lifetime can be extended to ∼2 years when stored under inert conditions at 50 °C. These results demonstrate that the rationally designed all-conjugated BCP can effectively modulate the BHJ morphology of an all-polymer blend to simultaneously enhance its photovoltaic performance and stability.

Organic carbon materials, such as graphene and nanotubes, with a high specific capacity show promise in improving the energy density for lithium ion batteries (LiBs). Here, we report on the synthesis and characterization of C60(OH)12 and the C60(OH)12/graphene oxide (GO) composite and demonstrate their use as anode materials in LiBs. We find that the C60(OH)12/GO composite forms due to the chemical reactions between the carboxyl and epoxy groups of GO and the hydroxyl of C60(OH)12 nanoparticles and that C60(OH)12 uniformly grows on the surface of GO nanosheets. Using a suite of spectroscopy probes, we unequivocally show the mixing between C60(OH)12 and GO at the molecular level, which leads to superior battery performances. This composite has a reversible capacity of 1596 mAh g-1 at 0.2 A g-1, higher than the capacities of C60(OH)12 and GO. This composite has a superior cycling stability and excellent rate performance, making it a promising organic anode material for high-performance LiBs.

Conjugated polyelectrolytes (CPEs) have developed as promising hole transport materials for perovskite solar cells (PSCs). The conjugated backbone serves as an efficient vehicle for transporting holes, and the electric dipole layer formed through the organization of ionic groups on CPEs may improve the hole collection efficiency. In this work, three CPEs anchored with –N(CH3)3+, –SO3− and –NH3+ ions, denoted as BF-NMe3, BF-SO3 and BF-NH3, respectively, were synthesized and applied as the hole transport material (HTM) of inverted planar PSCs. Replacing the benchmark material, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), with the three CPEs as the HTM considerably improves the photovoltaic performance of PSCs. The results from scanning electron microscope imaging, X-ray diffraction and time-resolved photoluminescence indicate that the structure of the ionic species rather than the type of charge has a decisive impact on the perovskite morphology. Both cationic BF-NH3 and anionic BF-SO3 layers enable methylammonium lead iodide (MAPbI3) to grow into larger crystals and grains with fewer defects. Moreover, the electrochemical impedance spectroscopy measurements demonstrate that the BF-NH3 and BF-SO3 devices have comparable charge recombination resistance, which is apparently higher than that of the BF-NMe3 and PEDOT:PSS devices. Consequently, the cationic BF-NH3 can act as an excellent HTM as the anionic BF-SO3 and the champion cell based on BF-NH3 exhibits a superior power conversion efficiency of 17.7%.

A study was carried out on the possibility of orderly and spontaneous dimerization at room temperature of C60 cages in fullerene liquid crystal fullerene dyads (R-C60). For this purpose, dyads with a structural elements feature supporting π-stacking and Van der Waals interactions were tested, due to the presence of terthiophene donors linked through an α-position or dodecyloxy chains. In addition, this possibility was also tested and compared to dyads with shorter substituents and the pristine C60. Research has shown that only in dyads with the features of liquid crystals, π-dimerization of C60 units occurs, which was verified by electrochemical and spectroelectrochemical (ESR) measurements. Cyclic voltammetry and differential voltammetry studies reveal π-dimerization in liquid crystal dyad solution even without the possibility of previous polymerization (cathodic or anodic) under conditions in the absence of irradiation and without the availability of reaction initiators, and even with the use of preliminary homogenization. These dyads undergo six sequential, one-electron reductions of π-dimer (R-C60···C60-R), where two electrons are added successively to each of the two fullerene cages and first form two radical anion system (R-C60)•−(R-C60)•− without pairing with the characteristics of two doublets. Similarly, the second reductions of π-dimer occur at potentials that are close to the reduction potential for the conversion to a system of two triplet dianions (R-C60)2−(R-C60)2−. Electron paramagnetic resonance spectra indicate a significant interaction between C60 cages. Interestingly, the strength of intermolecular bonds is so significant that it can overcome Coulombic repulsion, even with such highly charged particles as dianions and trianions. Such behavior has been revealed and studied so far only in covalently bonded C60 dimers.

A study was carried out on the possibility of orderly and spontaneous dimerization at room temperature of C60 cages in fullerene liquid crystal fullerene dyads (R-C60). For this purpose, dyads with a structural elements feature supporting π-stacking and Van der Waals interactions were tested, due to the presence of terthiophene donors linked through an α-position or dodecyloxy chains. In addition, this possibility was also tested and compared to dyads with shorter substituents and the pristine C60. Research has shown that only in dyads with the features of liquid crystals, π-dimerization of C60 units occurs, which was verified by electrochemical and spectroelectrochemical (ESR) measurements. Cyclic voltammetry and differential voltammetry studies reveal π-dimerization in liquid crystal dyad solution even without the possibility of previous polymerization (cathodic or anodic) under conditions in the absence of irradiation and without the availability of reaction initiators, and even with the use of preliminary homogenization. These dyads undergo six sequential, one-electron reductions of π-dimer (R-C60···C60-R), where two electrons are added successively to each of the two fullerene cages and first form two radical anion system (R-C60)•−(R-C60)•− without pairing with the characteristics of two doublets. Similarly, the second reductions of π-dimer occur at potentials that are close to the reduction potential for the conversion to a system of two triplet dianions (R-C60)2−(R-C60)2−. Electron paramagnetic resonance spectra indicate a significant interaction between C60 cages. Interestingly, the strength of intermolecular bonds is so significant that it can overcome Coulombic repulsion, even with such highly charged particles as dianions and trianions. Such behavior has been revealed and studied so far only in covalently bonded C60 dimers.

In this study, a new fully π-conjugated diblock copolymer comprising of major semicrystalline poly(3-butyl thiophene) (P3BT) and minor amorphous poly(2,5-dihexyloxy-p-phenylene) (PPP) block chains was rationally designed and further used as synergistic charge-transporting networks for PCBM based solar cells. The light-harvesting P3BT block was carefully chosen due to its high melting temperature and greater hole mobility to afford better thermal stability. Despite lower molecular weight P3BT block in the copolymer compared with that of a P3BT homopolymer counterpart, the copolymer exhibited long-range ordered fibrils with larger P3BT crystals and higher total crystallinity, indicating that the minor PPP chains promote the ordering and crystallization of P3BT. In addition, the strong immiscibility and difference in the crystallographic kinetics among the two main-chain moieties allow the copolymer/PCBM hybrid to spontaneously self-assemble into an interpenetrating nanostructure, while permitting PCBM nanoparticles to preferentially locate in the amorphous PPP domains to form bicontinuous conduits for efficient dual-charge transport. Notably, the copolymer/PCBM hybrids exhibited superior long term thermal stability against degradation and PCBM aggregation upon accelerated aging of the devices. At stringently high aging temperature of 180 °C for 4 h for a thermal stress test, the copolymer devices retain nearly 90% of their maximum PCE, whereas those of the reference P3BT/PCBM solar cells decrease severely to be less than 50% of their maximum. These results demonstrate the advantage of using thermally stable all π-conjugated block copolymers to provide substantial enhancement in charge dissociation, transport as well as extended thermal stability due to the nanoconfining effect of its self-assembled copolymer structure.

A polythiophene homopolymer with conjugated side chains (2D-PT) was applied as a hole transport material (HTM) of perovskite solar cells (PSCs). The all-conjugated two-dimensional structure effectively increases the ionization potential, realizing a high open-circuit voltage near 1 V for the 2D-PT-based PSC. Very interestingly, the two-dimensional wide-angle X-ray scattering measurements show that the 2D-PT molecules are self-assembled into ordered structure with a face-on dominant orientation and exhibit a hole mobility, which is ∼1.6 times faster than that of poly(3-hexylthiophene) (P3HT). Consequently, the power conversion efficiency of PSC is noticeably increased by ∼30% as 2D-PT replaces P3HT as HTM. Moreover, the densely packed 2D-PT slows down the moisture induced degradation of perovskite crystals, leading to a better environmental stability. This work demonstrates that two-dimensional non-donor-acceptor structural conjugated polymers can be utilized as promising HTM of PSCs.

Heterocyclic conjugated polymers BZCTVT and TAPTVT containing benzo[c]cinnoline (BZC) and tetraazapyrene (TAP), respectively, were prepared by using Stille coupling polymerization in microwave reactor. BZC and TAP act as acceptors and thiophene-vinylene-thiophene (TVT) acts as donors. Alkylated thiophene is the linker between acceptor and donor. This is the first time that tetraazapyrene was incorporated into conjugated polymers. The films of BZCTVT and TAPTVT showed maximum absorption wavelength at 522 and 534 nm, respectively. From cyclic voltammertry measurement, TAPTVT and BZCTVT exhibited low LUMO (−3.61 and −3.47 eV) and HOMO (−5.64 and −5.63 eV) energy levels. Even though BZC and TAP were planar structures, BZCTVT and TAPTVT showed large dihedral angles between alkylated thiophene and TVT (10.8–22.6°), and between alkylated thiophene and BZC and TAP (22.2–30.3°) based on their simulated energy-minimized geometry. The bottom-gate, top-contact OFETs based on TAPTVT and BZCTVT exhibited only p-channel behavior with hole mobility of 4.63 × 10−4 and 1.04 × 10−4 cm2 V−1 s−1 and current on/off ratios greater than 104 after thermal annealing. Grazing incidence X-ray diffraction (GIXRD) patterns suggested that thin films of TAPTVT and BZCTVT preferred edge-on orientation.

The power conversion efficiency of the perovskite solar cell is high enough to be commercially viable. However, long-term stability is the inevitable issue that obstructs its commercialization. Here, we demonstrate that the half-year (∼4680 h) stable unencapsulated inverted solar cell has almost zero loss in performance, measured under controlled environmental condition, when using montmorillonite (MMT)/CH3NH3PbI3 nanocomposite as photoactive layer. It yields up to 17.29% in power conversion efficiency, owing to the formation of an outstandingly dense gas permeation barrier of exfoliated MMT shell that effectively retards the moisture from penetrating into the perovskite. It is believed that this extensively modified device and low-cost architecture will compellingly lead to the timely commercialization of perovskite solar cells.

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approaches 19%, increasing research attention is being paid to enhancing the device's long-term stability. In this study, a robust interface engineering of graphene oxide nanosheets (GNS) is expounded on improving the thermal and photostability of non-fullerene bulk-heterojunction (NFA BHJ) OPVs to a practical level. Three distinct GNSs (GNS, N-doped GNS (N-GNS), and N,S-doped GNS (NS-GNS)) synthesized through a pyrolysis method are applied as the ZnO modifier in inverted OPVs. The results reveal that the GNS modification introduces passivation and dipole effects to enable better energy-level alignment and to facilitate charge transfer across the ZnO/BHJ interface. Besides, it optimizes the BHJ morphology of the photoactive layer, and the N,S doping of GNS further enhances the interaction with the photoactive components to enable a more idea BHJ morphology. Consequently, the NS-GNS device delivers enhanced performance from 14.5% (control device) to 16.5%. Moreover, the thermally/chemically stable GNS is shown to stabilize the morphology of the ZnO electron transport layer (ETL) and to endow the BHJ morphology of the photoactive layer grown atop with a more stable thermodynamic property. This largely reduces the microstructure changes and the associated charge recombination in the BHJ layer under constant thermal/light stresses. Finally, the NS-GNS device is demonstrated to exhibit an impressive T

Organic carbon materials, such as graphene and nanotubes, with a high specific capacity show promise in improving the energy density for lithium ion batteries (LiBs). Here, we report on the synthesis and characterization of C

Polycrystalline perovskite film-based X-ray detector is an appealing technology for assembling large scale imager by printing methods. However, thick crystalline layer without trap and solvent residual is challenging to fabricate. Here, the authors report a solution method to produce high quality quasi-2D perovskite crystalline layers and detectors that are suitable for X-ray imaging. By introducing n-butylamine iodide into methylammonium lead iodide precursor and coating at elevated temperatures, compact and crystalline layers with exceptional uniformity are obtained on both rigid and flexible substrates. Photodiodes built with the quasi-2D layers exhibit a low dark current and stable operation under constant electrical field over 96 h in dark, and over 15 h under X-ray irradiation. The detector responds sensitively under X-ray, delivering a high sensitivity of 1214 µC Gy

The electron transport layer of planar-heterojunction perovskite solar cells was produced by the ultrasonic spray pyrolysis (USP) of organotitanium precursors and the spin-coating of TiO2 sol-gel. Although the TiO2 products prepared from both methods have the same anatase crystal structure, the former route yields an ultra-compact, bulk-like film with reduced defects. Results from the electrochemical impedance spectroscopy measurements reveal the electron transfer resistance through the TiO2/CH3NH3PbIxCl3−x interface for the titanium oxide prepared by ultrasonic spray pyrolysis (TiO2-USP) method is lower than that for the titanium oxide prepared by sol-gel (TiO2-SG) method. Interesting, the TiO2-USP device exhibits relative low interfacial resistance of charge carrier through the CH3NH3PbIxCl3−x/spiro-OMeTAD interface as well. As a result, replacing TiO2-SG with TiO2-USP substantially improves the power conversion efficiency from 12.98% to 16.13%, demonstrating the USP is a facile approach to fabricate high-quality TiO2 for developing high-performance perovskite solar cells.

Organic/inorganic hybrid structures are promising systems for a variety of functional devices because of their low cost, light weight, and ease of large-scale production. However, the ability to co...

Bulk heterojunction (BHJ) perovskite solar cells have recently attracted increased interest because of a significantly enhanced interface between perovskite and the n-type material in the active layer for efficient charge separation and increased power conversion efficiency (PCE). [6,6]-Phenyl-C61-butyric acid methyl ester (PC61BM) is the most commonly used n-type material in BHJ perovskite solar cells owing to its high electron mobility. However, it is very difficult to fabricate BHJ perovskite films because of the poor solubility of PC61BM in the commonly used solvent dimethylformamide (DMF). In this study, we introduced two kinds of fluorinated PC61BM (3F-PC61BM and 5F-PC61BM) as n-type materials in a BHJ perovskite film, which have higher solubility in DMF than that of PC61BM. Thus, a BHJ perovskite film can be easily fabricated in one step using a single solvent in a BHJ precursor solution system for planar perovskite solar cells. A BHJ device with a high PCE of 16.17% can be obtained by adding 0.1 wt% of 3F-PC61BM in a perovskite precursor solution to fabricate a solar cell, which outperforms the PCE of 14.12% of the pristine device. However, the addition of 5F-PC61BM decreased the PCE to lower than that of the pristine device regardless of its amount. We systematically studied the effects of the amount and type of fluorinated PC61BM on the morphology of BHJ perovskite films using SEM, AFM, GISAXS and GIWAXS. The results reveal that 3F-PC61BM can fill the pinholes between perovskite grains and passivate the defects in the pristine film. Thus, the current density (Jsc) is greatly increased. On the other hand, the self-aggregation of 5F-PC61BM in BHJ perovskite films caused the films to be full of large voids, which led to poor device performance. The dense and flat surface morphology of BHJ perovskite films containing 3F-PC61BM can also prevent the permeation of moisture into grain boundaries and enhance the device stability. Therefore, the device could maintain 80% of its original efficiency over 550 hours without any encapsulation in comparison with 240 hours for the pristine device. Our results provide a novel strategy for fabricating high-PCE and high-stability BHJ perovskite solar cells for the production of low-cost solar cells in the near future.

When applying the voltage pulses (6 V) to the organic light-emitting diode based on tris(8-hydroxyquinolinato) aluminium (Alq 3 ) as the electron transporting layer, current density and luminance increased by 16% and 20%, respectively, by providing the reverse bias (−16 V) during the off-period. By using displacement current measurement, we can deduce that such an enhancement resulted from the interfacial positive charges trapped at the Alq 3 /cathode interface, with the relaxation time ∼0.4 ms. By doping the organic material as the carrier trapping sites at Alq 3 /cathode interface, such current density and luminance increase can be further enhanced. 25% and 36% increase in current density and luminance was demonstrated with such driving technique, respectively.

The impact of the morphological stability of the donor/acceptor mixture under thermal stress on the photovoltaic properties of bulk heterojunction (BHJ) solar cells based on the poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]-dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]-thiophene)-2-carboxylate-2,6-diyl]/phenyl-C61-butyric acid methyl ester (PTB7-Th/PC61BM) blend is extensively investigated. Both optical microscopy and transmission electron microscopy micrographs show that long-term high-temperature aging stimulates the formation of microscale clusters, the size of which, however, is about 1 order of magnitude smaller than those observed in thermally annealed poly(3-hexylthiophene)/PC61BM composite film. The multilength-scale evolution of the morphology of PTB7-Th/PC61BM film from the scattering profiles of grazing incidence small-angle and wide-angle X-ray scattering indicates the PC61BM molecules spatially confine the self-organization of polymer chains into large doma...

Summary The irreversible phase transition by water incorporation, along with thermal decomposition, has long been thought to be the dominant degradation pathway to deteriorate electronic and optoelectronic properties of perovskite devices. However, comprehensive characterization and insightful understanding of beneficial effect of water incorporation remains scarce. Here, we capture the phase transformation of perovskite in situ from its precursor stage to the final film upon thermal annealing as a function of relative humidity (RH) by grazing-incident wide-angle X-ray scattering. Quantitative structural analyses show that a moderate water content (RH 40%) enhances the texture orientation of the perovskite. A consequence of the guided water-incorporated treatment is that the unencapsulated device, without any sophisticated instability-mitigation approaches, exhibits excellent tolerance to long-term, light soaking and high-temperature aging, retaining more than 80% of the peak power-conversion efficiency under constant 1-sun illumination or heating at 65°C for more than 1,000 h, respectively.

Developing highly planar semiconducting polymer is essential for achieving high mobility and improving the photovoltaic performance of bulk-heterojunction polymer solar cells. In this contribution, two novel low-bandgap donor-acceptor copolymers, P1-3T and P2-3T2F, consisting of electron-accepting benzothiadiazole acceptor segment and electron-donating terthiophene donor segment with and without fluorine atoms were designed and synthesized. The density functional theory calculations and ultraviolet–visible absorption studies demonstrate that the fluorinated P2-3T2F polymer has more planar backbone conformation, deeper HOMO level, broader absorption spectrum with a vibronic shoulder peak, and higher absorption coefficient compared with the non-fluorinated analogue polymer, P1-3T. Furthermore, P2-3T2F exhibits good crystallinity and high hole mobility, presumably due to the well-ordered lamellar packing and the π-π stacking interaction between the backbones of the conjugated polymers. The optimized polymer solar cell based on P2-3T2F:PC61BM exhibits a short-circuit current density (Jsc) of 12.77 mA cm−2, a fill factor (FF) of 68.99%, an open-circuit voltage (Voc) of 0.80 V, and a maximum power conversion efficiency (PCE) of 7.14%, which is approximately 46% higher than that of the P1-3T:PC61BM device. The enhanced PCE is primarily due to increased light-harvesting ability and interconnected morphology with finely dispersed polymer-rich and PC61BM-rich domains, which improves the efficiency of exciton dissociation and rises the mobility of charge carriers, thus boosting the short-circuit current density and the FF value. Moreover, the relatively deep HOMO of P2-3T2F effectively increases the Voc.

Crystallinity and crystal orientation have a predominant impact on a materials’ semiconducting properties, thus it is essential to manipulate the microstructure arrangements for desired semiconducting device performance. Here, ultra‐uniform hole‐transporting material (HTM) by self‐assembling COOH‐functionalized P3HT (P3HT‐COOH) is fabricated, on which near single crystal quality perovskite thin film can be grown. In particular, the self‐assembly approach facilitates the P3HT‐COOH molecules to form an ordered and homogeneous monolayer on top of the indium tin oxide (ITO) electrode facilitate the perovskite crystalline film growth with high quality and preferred orientations. After detailed spectroscopy and device characterizations, it is found that the carboxylic acid anchoring groups can down‐shift the work function and passivate the ITO surface, retarding the interface carrier recombination. As a result, the device made with the self‐assembled HTM show high open‐circuit voltage over 1.10 V and extend the lifetime over 4,300 h when storing at 30% relative humidity. Moreover, the cell works efficiently under much reduced light power, making it useful as power source under dim‐light conditions. The demonstration suggests a new facile way of fabricating monolayer HTM for high efficiency perovskite devices, as well as the interconnecting layer needed for tandem cell., Self‐assembled P3HT‐COOH is an excellent hole extraction layer to fabricate robust, high‐performance, and extremely reproducible perovskite solar cells. The well‐aligned self‐assembled P3HT‐COOH generates a dipole layer between indium tin oxide and perovskite, substantially retarding interface charge recombination and producing highly sensitive devices to dim light. The enhanced crystallinity and preferred out‐of‐plane orientation play a key role to suppress the device degradation process.

In this study, we report on the synthesis and self-assembling behavior of a series of monodisperse all π-conjugated poly(2,5-dihexyloxyp-phenylene)-block-(3-hexylthiophene) (PPP-P3HT) block copolymer system and construct its phase diagram that exhibits diverse nanostructures of predominant PPP nanofibers, PPP-P3HT lamellae, broken lamellae and predominant P3HT nanofibers as a function of the copolymer composition. An order-to-disorder phase transition is also observed for the copolymers at a temperature above the melting point of the predominant blocks, indicating the rod-rod interaction between the corresponding π-conjugated chains plays a key role in the formation and the stabilization of the observed nanostructures. In particular, we have also found that the incorporation of PPP segments to P3HT to form nanofibrillar structure significantly enhance the self-organization behavior of the P3HT in the copolymer. The improvements in crystallinity and mobility for the copolymers therefore substantially enhance their solar cell performance. The use of this novel material with diverse nanostructures provides a new strategy to enhance photovoltaic performance and shows the potential for use in future optoelectronic applications.

Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3–xClx perovskite in cross-sectional geometry. Two electronic phases, 10–20 nm in size, with different electronic properties inside the CH3NH3PbI3–xClx perovskite layer are observed by the dI/dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at −2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).

Two novel donor–acceptor (D–A) copolymers P1 and P2 with the thiazoloquinoxaline repeating acceptor moiety and different donor moieties of benzo[1,2-b:4,5-b']dithiophene and isomeric benzo[2,1-b:3,4-b']dithiophene have been prepared. The polymers show light absorption at 300–1200 nm and a band gap width of 0.98 and 1.14 eV, respectively. The energies of the HOMO (–5.42 and–5.29 eV) and LUMO (–3.90 and–3.83 eV) levels of polymers P1 and P2 have been determined. The absorption maximum for polymer P1 in the long-wavelength region is red-shifted by 161 nm, which is caused by stronger charge transfer in P1 as compared with P2. This fact indicates that the benzo[1,2-b:4,5-b']dithiophene structural moiety has a higher electron-donating ability than the benzo[2,1-b:3,4-b']dithiophene moiety. The red shift of the absorption spectrum of polymer P1 in comparison with that of P2 indicates that interchain π–π stacking interactions are more efficient in P1 than in P2.

Molecular engineering on the conjugated side chains of two-dimensional (2D) conjugated polymers was conducted and its effect on the optical, electronic, self-assembly and photovoltaic properties was investigated. A new monomer, M2, was prepared by capping (E)-3′-(2-(2,5-dibromothiophen-3-yl)vinyl)-4,4′′-bis(2-ethylhexyl)-2,2′:5′,2′′-terthiophene, M1, with two heptanoyl groups, and then coupled with 5,5′-bis(trimethylstannyl)-2,2′-bithiophene via microwave-assisted Stille polymerization to produce a series of polythiophene derivatives with terthiophene-vinylene conjugated side chains, TTV–PTs. Copolymer P2 shows a down-shifted HOMO energy level, enhanced solubility, and red-shifted absorption, as compared with P1; however, the bulky side chains significantly disrupt the coplanarity of thiophene rings in the polymer backbone and the ability to self-assemble into an ordered structure. The GIXRD measurements reveal that the original crystallinity of P1 can be recovered by simply inserting a few 2,1,3-benzothiadiazole units into the polythiophene main chain in P2 through a random copolymerization route to yield a terpolymer, P3, which possesses excellent crystallinity, thereby causing a three-fold increment in hole mobility. Furthermore, the P1/PC_(61)BM, P2/PC_(61)BM, and P3/PC61BM solar devices exhibit power conversion efficiencies of 3.89%, 1.52%, and 4.17%, respectively, under AM1.5G illumination with an intensity of 100 mW cm^(−2).

We designed and synthesized a novel series of two-dimensional (2D) conjugated polymers (P1-2T, P2-2T2F and P3-4T2F) containing 2,2′-bithiophene (2T) and 3,3′-difluoro-2,2′-bithiophene (2T2F) as donor units, and 4,7-benzo[c][1,2,5]thiadiazole (BT) and 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT) as acceptor units appended with conjugated vinyl-terthiophene (VTT) side chain. We comprehensively investigated the effect of fluorination and thiophene (T) π-spacer on the optoelectronic properties and photovoltaic performance of the resulting copolymers. In comparison with non-fluorinated polymer P1-2T, the fluorinated polymer P2-2T2F and P3-4T2F had down shifted highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels with an enhanced absorption band. Moreover, 2D grazing incidence wide-angle X-ray scattering and space charge limited current measurement showed that the presence of thiophene π-spacer in P3-4T2F promoted dominant face-on orientation, high crystallinity and enhanced hole mobility, compared with P2-2T2F. As a result, the inverted polymer solar cell based on the P3-4T2F:PC61BM blend exhibited a high power conversion efficiency (PCE) of 6.66% with a Jsc of 12.99 ± 0.30 mA/cm−2. In contrast, the P1-2T:PC61BM and P2-2T2F:PC61BM devices without π-spacer showed a PCE of 2.22% and 0.95%, respectively. The PCE of the P3-4T2F:PC61BM device was further improved to 6.89% by using a polyethylenimine ethoxylated (PEIE) interlayer between ITO and ZnO. This study reinvigorates the key modulation of a 2D conjugated polymer with improved photovoltaic performance.

A series of layered-structure perovskite solar cells with three different HTM layers consisting of P3HT, PBTTTV-h, and spiro-OMeTAD were fabricated to investigate intermolecular and interfacial def...

Ion accumulation of organometal halide perovskites (OHPs) induced by electrode polarization of perovskite solar cells (PSCs) under illumination has been intensely studied and associated with a widely observed current–voltage hysteresis behavior. This work is dedicated to the investigation of the behavior of charged species at the compact TiO2/OHP interface with respect to electrode polarization in PSC devices. By providing a comprehensive discussion of open-circuit voltage (VOC) buildup and VOC decay under illumination and in the dark for the PSCs modified with [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) at the TiO2/OHP interface and their corresponding electrochemical impedance spectroscopies (EISs), a justified mechanism is proposed attempting to elucidate the dynamics of interfacial species with respect to the time and frequency domains. Our results demonstrate that the retarded VOC buildup and decay observed in PSC devices are related to the formation of bound charges in TiO2, which is essential...

A new approach to largely enhancing light harvesting of solar cells by employing bifunctional polymer nanocomposites as hole-transport layers (HTLs) is proposed. To illustrate our working principle, CH3NH3PbI3-xClx perovskite solar cells are used as examples. Gold nanoparticles (Au-NPs) are added into a conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) matrix, resulting in a ∼4-fold enhancement in the electrical conductivity and carrier mobility of the native P3HT film. The improved electrical properties are attributed to enhanced polymer chain ordering caused by Au-NPs. By integration of those P3HT:Au-NP films with an optimum loading concentration of 20% into perovskite solar cells as HTLs, this leads to a more than 25% enhancement in the power conversion efficiency (PCE) compared with that of the NP-free one. In addition to the modulated electrical properties of the HTL, the improved performance can also be attributed to the scattering effect from the incorporated Au-NPs, which effectively extends the optical pathway to amplify photon absorption of the photoactive layer. The design principle shown here can be generalized to other organic materials as well, which should be very useful for the further development of high-performance optoelectronic devices.

In this study, we demonstrate the cooperative self-assembly of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and an all-conjugated poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-hexylthiophene) (PPP-P3HT) block copolymer to yield organic photovoltaic devices with enhanced solar cell performance and long-term stability. By a combination of TEM, GISAXS and GIWAXS structural investigations, it was found that a PPP-P3HT/PCBM hybrid film adopts a donor/acceptor (D/A) double-channel network (DCN) structure via simple spin-coating by self-organizing highly ordered and long-ranged crystalline P3HT nanofibrils as a hole-transporting channel, and the surrounding amorphous PPP domain with PCBM confined and dispersed within as the other electron-transporting channel. As a consequence of the structural development, the block copolymer hybrid solar cells could afford significant improvements in the charge transporting property and enhanced exciton separation, leading to a substantial improvement in the power conversion efficiency (PCE) of the resulting device. The photovoltaic devices with the DCN structure gave a high average PCE of 3.43% as compared to only 2.77% from a conventional P3HT/PCBM bulk heterojuction (BHJ) solar cell. Notably, the DCN solar cell showed significant improvements in thermal stability over the P3HT/PCBM BHJ solar cell in accelerated testing experiments. This enhancement is believed to be due to the nanoconfinement effect of the double-channel structure on the PCBM molecules, thereby averting PCBM aggregation problems typically occurring in BHJ devices. These results show promise for the practical usage of all-conjugated block copolymers with different main chain moieties towards the fabrication of organic photovoltaic devices with superior stability and competitive optoelectronic properties.

In this communication, glycine, an amino acid, was applied to modify the TiO2/CH3NH3PbI3 heterojunction interface for reducing the inevitable defects formed during crystallization of perovskite. The power conversion efficiency of the resulting perovskite solar cell was increased from 8.35 to 12.02%, attributed to the enhancement of the short-circuit current density.

Novel two-dimensional conjugated copolymer, abbreviated as PDTBSeVTT-2TF, containing electron-deficient 4,7-di(thiophen-2-yl)benzo[c][1,2,5]selenodiazole (DTBSe) unit, conjugated vinyl-terthiophene (VTT) side chain and 3,3′-difluoro-2,2′-bithiophene (2TF) was designed and synthesized using microwave-assisted Stille cross-coupling polymerization. UV–visible absorption and cyclic voltammetry studies revealed that this copolymer possesses a strong and broad absorption in the range of 300–800 nm and a narrow optical bandgap (Eg) of 1.57 eV with low-lying HOMO and LUMO energy levels. Further, the bulk heterojunction polymer solar cells (PSCs) were fabricated using PDTBSeVTT-2TF as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor with an inverted device structure of ITO/ZnO/PDTBSeVTT-2TF:PC71BM/V2O5/Ag. The processing temperature of blend solution for preparing PDTBSeVTT-2TF:PC71BM active layer showed obvious impact on the photovoltaic performance of solar devices. The cell fabricated from the blend solution at 65 °C exhibited enhanced power conversion efficiencies (PCE) of 5.11% with a Jsc of 10.99 mA/cm−2 compared with the one at 50 °C, which had a PCE of 4.69% with a Jsc of 10.10 mA/cm−2. This enhancement is due to the dissolution of PDTBSeVTT-2TF clusters into single molecules and small aggregates, improving the miscibility between the polymer and PC71BM and thus increasing the donor/acceptor interface.

A series of new fulleropyrrolidines, which comprise one terthiophene (3T) or dithienyl thienothiophene (2TTT) conjugated segment along with two hexyl (H) or ethylhexyl (EH) chains, abbreviated as 3T-H-C60, 3T-EH-C60, 2TTT-H-C60 and 2TTT-EH-C60, were designed and synthesized to improve their structural compatibility with poly(3-hexylthiophene) (P3HT). These [60]fullerene monoadducts exhibit a characteristic UV–Vis absorption band, associated with the conjugated substituent, and similar optical bandgaps and lowest unoccupied molecular orbital (LUMO) levels of approximately 1.71 eV and −3.72 eV, respectively. The influence of the structure of the substituent in the fulleropyrrolidine on its intermolecular packing within a polymer matrix was investigated. Photoluminescence measurements of the blended films of such C60 derivatives with P3HT reveal that the interfacial area between the two materials is larger in the 3T-based system than in the 2TTT-based system; moreover, the branched ethylhexyl chain is more effective than the linear hexyl group in reducing the size of the phase domains. Transmission electron microscopic images further confirm that relatively serious phase segregation occurs in the 2TTT-C60/P3HT films. Accordingly, solar cells with 3T-C60/P3HT as the active layer have an increased short-circuit current density owing to improved exciton dissociation efficiency, but 2TTT-C60/P3HT devices have a boosted fill factor, owing to the formation of less obstructed pathways for the transport of charge carriers. More interestingly, both 3T-EH-C60/P3HT and 2TTT-EH-C60/P3HT exhibit highly stable blend morphology and the solar cells that are derived from them have extremely steady power conversion efficiency against long-term aging at high temperature.

In this study, we demonstrate a facile in situ synthetic strategy to fabricate self-assembled organic/inorganic hybrid nanowires, wherein a “pre-crystallization” approach was first utilized to co-organize P3HT molecules and zinc precursors into highly elongated nanowires, followed by a thermal oxidation treatment to directly grow ZnO nanocrystals on the existing nanofibrillar template. By further thermal annealing the ZnO embossed hybrid nanowires, a unique superhighway-like architecture which composed of alternating parallel channels of P3HT nanofibrils and ZnO nanocrystals could be further obtained. This donor/acceptor (D/A) parallel-channel structure gave access to the improvements in the exciton dissociation and charge transport, thereby enhancing photoluminescence quenching, charge transport, and device performance. The photovoltaic devices with the D/A parallel-lane structure gave a high PCE of 0.61% as compared to only 0.07% from a conventional P3HT/ZnO bulk heterojuction solar cell. Our approach o...