Grazing Incidence Wide-angle X-ray Scattering Research Articles

Hyper 100 °C Langmuir-Blodgett (Langmuir-Schaefer) Technique for Organized Ultrathin Film of Polymeric Semiconductors.

In this study, we advanced the conventional Langmuir-Blodgett (LB) method to a high-temperature range (above 100 °C) using a newly manufactured LB machine, which is adaptable to a high-boiling-point subphase, as a universally usable apparatus. A sophisticated trough design, with homogeneous heating capability up to approximately 200 °C, together with automatic film compression and Langmuir-Schaefer type film transfer, enabled the fabrication of highly aligned thin films of polymeric semiconductors with uniaxial alignment of polymer backbones, which is desirable for efficient charge transport. Herein, ultrathin films of semicrystalline thiophene-based semiconductors were prepared on ethylene glycol and heated to 80 °C. The analyses of the transferred films with pressure-area isotherms, atomic force microscopy (AFM), polarized optical microscopy (POM), and grazing-incidence wide-angle X-ray scattering (GIWAXS) indicated that the proposed high-temperature LB method allows ideal deposition of high-quality ultrathin films with molecular layer precision at the selected high-temperature conditions. Furthermore, preparing thin-film donor-acceptor-type copolymers in ionic liquids at high temperatures (up to 140 °C) was a challenging task that was successfully demonstrated in this study. Highly ordered thin films of donor-acceptor polymers with a uniaxial backbone orientation were obtained only at 140 °C. The obtained semicrystalline thin films with uniaxially aligned polymer backbones significantly contribute to the two-dimensional overlap of molecular orbitals, which is likely to promote charge transport. The use of the manufactured automatic LB machines is advantageous for better quality films prepared at higher temperatures (even above 100 °C) from various technical viewpoints, including homogeneous heating, constant compression, and automatic film transfer. The novel methodology proposed herein expands the possibilities of the Hyper 100 °C Langmuir-Blodgett technique, which has not been accessible by the conventional LB method with the aqueous subphase.

Green-Solvent-Processable Organic Photovoltaics with High Performances Enabled by Asymmetric Non-Fullerene Acceptors.

In this work, two asymmetric non-fullerene acceptors (NFAs), BTP-EHBO-4F and BTP-PHD-4F, are designed to be applied in green-solvent-processable organic photovoltaics (OPVs). BTP-EHBO-4F and BTP-PHD-4F show good solubilities in green solvent o-xylene. As a result, PM6:BTP-EHBO-4F-based devices exhibit outstanding photovoltaic performances using o-xylene as a solvent. By comparison, due to the poor solubility of Y6 in o-xylene, PM6:Y6-based devices show poor performances. Owing to the favorable phase separation, molecule packing, and orientation observed from atomic force microscopy (AFM) and grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements, PM6:BTP-PHD-4F-based devices demonstrate a PCE of 15.91% with a VOC of 0.87 V, a JSC of 25.64 mA/cm2, and an FF of 71.34%. Moreover, PM6:BTP-EHBO-4F-based devices exhibit an impressive PCE of 16.82% with a VOC of 0.85 V, a JSC of 26.12 mA/cm2, and an FF of 75.78%, which is outstanding for OPVs using o-xylene as a solvent.

Temperature-Dependent Crystallization Mechanisms of Methylammonium Lead Iodide Perovskite From Different Solvents

Hybrid perovskites are a novel type of semiconductors that show great potential for solution-processed optoelectronic devices. For all applications, the device performance is determined by the quality of the solution-processed perovskite thin films. During solution processing, the interaction of solvent with precursor molecules often leads to the formation of solvate intermediate phases that may diverge the crystallization pathway from simple solvent evaporation to a multi-step formation process. We here investigate the crystallization of methylammonium lead iodide (MAPbI3) from a range of commonly utilized solvents, namely dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and gamma-butyrolactone (GBL) at different temperatures ranging from 40°C to >100°C by in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. For all solvents but GBL, we clearly observe the formation of solvate-intermediate phases at moderate processing temperatures. With increasing temperatures, an increasing fraction of the MAPbI3 perovskite phase is observed to form directly. From the temperature-dependence of the phase-formation and phase-decomposition rates, the activation energy to form the MAPbI3 perovskite phase from the solvate-phases are determined as a quantitative metric for the binding strength of the solvent within the solvate-intermediate phases and we observe a trend of DMSO > DMF > NMP > GBL. These results enable prediction of processing temperatures at which solvent molecules can be effectively removed.

Morphology and Charge Transport Properties of P(NDI2OD-T2)/Polystyrene Blends

While the strategy of blending commodity insulating polymers with conjugated polymers has been previously applied to modify the properties of organic field-effect transistors (OFETs), comprehensive studies on the evolution of morphology and OFET performance with film composition are scarce. In this contribution, films comprising the n-type semiconducting polymer P(NDI2OD-T2) and the insulating polymer polystyrene (PS) are explored in detail. In particular, the electrical properties and film morphology of blends with a P(NDI2OD-T2) concentration ranging from 0.125 to 100 wt % are studied. Two regimes characterized by distinct dependencies of device mobility as a function of P(NDI2OD-T2) content are observed: Above 12.5 wt % P(NDI2OD-T2), the OFET mobility exhibits a weak dependence on P(NDI2OD-T2) concentration despite the presence of strong lateral phase separation, while below 12.5%, the device mobility is observed to decrease strongly with decreasing P(NDI2OD-T2) concentration attributed to disrupted surface connectivity of the P(NDI2OD-T2) phase. UV–vis absorption spectroscopy and grazing incidence wide-angle X-ray scattering (GIWAXS) measurements indicate that the aggregation and crystalline packing are not strongly affected by the presence of PS. Atomic force microscopy and scanning transmission X-ray spectro-microscopy reveal lateral phase separation for blends with compositions of 87.5 to 25 wt % P(NDI2OD-T2). Enrichment of P(NDI2OD-T2) at the film surface is confirmed by near-edge X-ray absorption fine structure spectroscopy, with a high P(NDI2OD-T2) surface composition (>80 wt %) maintained down to an overall blend composition of 12.5 wt % P(NDI2OD-T2). The strong decrease in OFET mobility for P(NDI2OD-T2) concentration less than 25 wt % is attributed to a loss of P(NDI2OD-T2) surface connectivity at low P(NDI2OD-T2) loading. We also observe a transition from face-on to edge-on dominated configuration at low P(NDI2OD-T2) content with GIWAXS, consistent with an edge-on surface layer that persists down to monolayer surface coverage.

To Fluorinate or Not to Fluorinate in Organic Solar Cells: Achieving a Higher PCE of 15.2% when the Donor Polymer is Halogen‐Free

AbstractFluorination of the donor and/or acceptor blocks of photoactive semiconducting polymers is a leading strategy to enhance organic solar cell (OSC) performance. Here, the effects are investigated in OSCs using fluorine‐free (TPD‐3) and fluorinated (TPD‐3F) donor polymers, paired with the nonfullerene acceptor Y6. Interestingly and unexpectedly, fluorination negatively affects performance, and fluorine‐free TPD‐3:Y6 OSCs exhibit a far higher power conversion efficiency (PCE = 14.5%) than in the fluorine‐containing TPD‐3F:Y6 blends (PCE = 11.5%). Transmission electron microscopy (TEM) analysis indicates that the TPD‐3F:Y6 blends have larger phase domain sizes than TPD‐3:Y6, which reduces exciton dissociation efficiency to 81% for TPD‐3F:Y6 versus 93% for TPD‐3:Y6. Additionally, grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals that the TPD‐3F:Y6 blends are less textured than those of TPD‐3:Y6, while space‐charge limited currents reveal lower and unbalanced hole/electron mobility in TPD‐3F:Y6 versus TPD‐3:Y6 blends. Charge recombination dynamic, transient absorption, and donor–acceptor miscibility assays additionally support this picture. Furthermore, conventional architecture TPD‐3:Y6 OSCs deliver a PCE of 15.2%, among the highest to date for halogen‐free polymer donor OSCs. Finally, a large‐area (20.4 cm2) TPD‐3:Y6 blend module exhibits an outstanding PCE of 9.31%, one of the highest to date for modules of area >20 cm2.

(Invited) Vacuum Deposition and Crystal Growth of Organolead Halide Perovskite

Perovskite solar cells are developing very rapidly and have attracted much attention because of their high power-conversion efficiencies (PCE). Fabrication control of perovskite crystal is important because the reproducibility of the device performance is important issue for perovskite solar cells. We have been focusing on vacuum deposition for the precise control of the fabrication of perovskite. We demonstrated that laser deposition method is useful for the precise deposition-rate control of methylamine iodide[1], where its high vapor pressure makes it difficult to control its deposition rate by conventional deposition method. By taking the advantage of deposition control, we focused on the crystal growth and crystal-growth analysis of perovskite. In this paper, the technical aspects of laser deposition method will be addressed, followed by fabrication of perovskite solar cells [1], epitaxial growth [2] and growth dynamics analysis using laser deposition method.Firstly, we implemented laser deposition for the deposition of perovskite, where the source materials (PbI2, CH3NH3I) were heated with the IR continuous-wave laser. The PID control system was implemented to adjust the deposition rate and the stabilized evaporation rate was achieved. Perovskite solar cells were constructed using the cell structure of ITO/PEDOT:PSS/NiOx/PCDTBT/CH3NH3PbI3/PCBM/BCP/Al and power conversion efficiency of 16% was obtained.Next, we attempted epitaxial growth of CH3NH3PbI3 on (1 0 0) oriented rubrene single crystals to obtain highly ordered perovskite crystal. We succeeded in the epitaxial growth of perovskite both by a co-deposition method and an alternative deposition method. The precise crystal orientation and crystallization dynamics were analyzed using grazing incident wide angle X-ray scattering (GIWAXS) at a synchrotron radiation facility (SPring-8, BL46XU).

Combined in Situ Photoluminescence and X-ray Scattering Reveals Defect Formation in Lead-Halide Perovskite Films.

Lead-halide perovskites have established a firm foothold in photovoltaics and optoelectronics due to their steadily increasing power conversion efficiencies approaching conventional inorganic single-crystal semiconductors. However, further performance improvement requires reducing defect-assisted, nonradiative recombination of charge carriers in the perovskite layers. A deeper understanding of perovskite formation and associated process control is a prerequisite for effective defect reduction. In this study, we analyze the crystallization kinetics of the lead-halide perovskite MAPbI3-xClx during thermal annealing, employing in situ photoluminescence (PL) spectroscopy complemented by lab-based grazing-incidence wide-angle X-ray scattering (GIWAXS). In situ GIWAXS measurements are used to quantify the transition from a crystalline precursor to the perovskite structure. We show that the nonmonotonous character of PL intensity development reflects the perovskite phase volume, as well as the occurrence of the defects states at the perovskite layer surface and grain boundaries. The combined characterization approach enables easy determination of defect kinetics during perovskite formation in real-time.

Crystalline Domain Formation to Enable High-Performance Polymer Thermoelectrics Inspired by Thermocleavable Materials.

Improving the electrical conductivity is an important role in realizing high thermoelectric performance of solution-processable polymers. Herein, a simple and robust approach to boost the mobility and doping efficiency of a diketopyrrolopyrrole-based copolymer with the introduction of thermocleavable side chains (PDPPS-X, where X is the molar ratio of the thermocleavable side chains and alkyl chains) is first provided. Notably, the incorporated thermocleavable groups can be effectively removed after thermal treatment and therefore contribute to the crystalline domain formation via hydrogen-bonded networks, which is critical for conductivity enhancements. Grazing incidence wide-angle X-ray scattering (GIWAXS) patterns give a clear indication that the thermal treatment of PDPPS-5 can greatly improve the structural arrangement, resulting in a significantly enhanced hole mobility (5.4 times that of PDPPS-0 without thermocleavable chains). Compared to PDPPS-0, a larger Fermi level shift is observed after doping PDPPS-5 with FeCl3, reflecting a better doping efficiency. Consequently, remarkably improved conductivity and power factor are achieved by PDPPS-5 after doping with 0.03 M FeCl3 at room temperature, which are about 2.2 and 3.5 times higher than that of PDPPS-0 at the same testing condition, respectively. Moreover, PDPPS-5 achieved a maximum power factor of 57.5 μW m-1 K-2 at 404 K.

Improved photovoltaic properties of copolymer donors by regulating alkyl and alkylsilyl side chains

By changing the ratio of alkyl and tripropylsilyl side chain of the donor unit, a series of copolymer donor materials, named PBT1, PBT10Si, PBT20Si, PBT30Si and PBDB-Si, are synthesized and applied in polymer solar cells (PSCs). All copolymers exhibit complementary absorption spectra and matched energy levels with small molecular acceptor Y6. Grazing incidence wide angle X-ray scattering (GIWAXS) measurements demonstrate that all copolymer pure films and blend films show distinct face-on orientations. Whereas, the blend film based on PBT20Si:Y6 manifests appropriate phase separation and less bimolecular recombination, which is in favor of effective exciton disintegration and charge transfer. As a result, the PBT20Si-based device exhibits a relatively high hole mobility (μh) value of 4.99 × 10−4 cm2 V−1 s−1, and obtains the highest power conversion efficiency (PCE) of 13.06%. These results indicate that the moderate introduction of tripropylsilyl side chains into polymer donors can improve the molecular aggregation and suppress bimolecular recombination of the photoactive layer, which is an effective strategy worthy of further research to promote the device performances.

A Systematic Review of Metal Halide Perovskite Crystallization and Film Formation Mechanism Unveiled by In Situ GIWAXS.

Metal halide perovskites are of fundamental interest in the research of modern thin-film optoelectronic devices, owing to their widely tunable optoelectronic properties and solution processability. To obtain high-quality perovskite films and ultimately high-performance perovskite devices, it is crucial to understand the film formation mechanisms, which, however, remains a great challenge, due to the complexity of perovskite composition, dimensionality, and processing conditions. Nevertheless, the state-of-the-art in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) technique enables one to bridge the complex information with device performance by revealing the crystallization pathways during the perovskite film formation process. In this review, the authors illustrate how to obtain and understand in situ GIWAXS data, summarize and assess recent results of in situ GIWAXS studies on versatile perovskite photovoltaic systems, aiming at elucidating the distinct features and common ground of film formation mechanisms, and shedding light on future opportunities of employing in situ GIWAXS to study the fundamental working mechanisms of highly efficient and stable perovskite solar cells toward mass production.

Systematic Investigation of Solution-State Aggregation Effect on Electrical Conductivity in Doped Conjugated Polymers

Systematic Investigation of Solution-State Aggregation Effect on Electrical Conductivity in Doped Conjugated Polymers

Favorable grain growth of thermally stable formamidinium-methylammonium perovskite solar cells by hydrazine chloride

Formamidinium methylammonium lead iodine (FAMAPbI3) based perovskite solar cells have reached phenomenal efficiencies recently. However, it is difficult to form pure black α-phase perovskite by solution method. Meanwhile, the formed polycrystalline FAMAPbI3 film often has large amount of grain boundaries, which can consist dangling bonds and iodide ions. Under illumination and heat, iodide ions can easily migrate and oxidize to form iodine, thus decompose the structure of perovskite and reduce the device performance. Herein, hydrazine chloride (HACl) as an additive is employed to promote favorable grain orientation during the growth of perovskite crystals. From grazing incidence wide-angle X-ray scattering (GIWAXS) and scanning electron microscope (SEM), HACl can facilitate strong diffraction signals along crystallographic planes (100) and (200) indicating a strengthened lattice structure for α-phase FAPbI3 and significantly decrease the grain boundaries for reduced carrier recombination. Consequently, the perovskite solar cells (PSCs) with optimized content of HACl lead to a champion power conversion efficiency (PCE) of 22.32% (certified PCEs of 21.59%) in a mesoporous device based on (FAPbI3)0.95(MAPbBr3)0.05 perovskite solar cells. Furthermore, from UV–vis and XPS spectrum, HACl can reduce iodine (I0) to iodide (I-) effectively, meaning the process of decomposition of FAMAPbI3-based perovskite has been greatly inhibited. As a result, unencapsulated device can retain 95% of its original power conversion efficiency after 1400 h of continuous one-sun illumination. Meanwhile, thermal (60 °C) stability is also greatly improved by maintaining 90% of initial efficiency after aging for 1400 h.

Efficient application of intermediate phase for highly-oriented MAPbI3 perovskite solar cells in ambient air

Although the efficiency of inorganic-organic perovskite solar cells (PSCs) has increased significantly owing to intermediate phase induced slow crystallization using dimethyl sulfoxide (DMSO) as a co-solvent in N2-filled glovebox, PSCs are generally fabricated in ambient air via a fast crystallization process to protect the perovskite layer from H2O or O2. In this study, we suggest a possibility of slow crystallization process for MAPbI3 perovskite crystals via intermediate phase formation by adjusting the humidity of air at RH 20%–30%. We obtained high-quality perovskite grains by implementing the slow crystallization process using an antisolvent and the ratio of PbI2:MAI:DMSO in the precursor solution at RH 20%–30%. The amount and state of the intermediate phase inside the as-deposited film were analyzed by grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. The deposited perovskite layer with the pure intermediate via extremely slow crystallization showed higher absorption, fewer grain boundaries, and suppressed defect recombination losses than the fast crystallized perovskite phase. Thus, we obtained higher stability and high power conversion efficiency of up to 18.56% in a p-i-n-structured MAPbI3-based perovskite solar cell under ambient air with RH 20%–30%.

Surface-Orientation Elimination of Vapor-Deposited PbI2 Flakes for Efficient Perovskite Synthesis on Curved Solar Cells.

Vapor deposition of perovskite solar cells (PSCs) has attracted considerable interest for its dry processing characteristics. However, a two-step sequential vapor deposition method suffers from ineffective conversion of PbI2 to perovskite with reasons still unclear. In this report, we carefully investigated the crystallization orientation of PbI2 films deposited by physical vapor deposition via synchrotron grazing-incidence wide-angle X-ray scattering (GIWAXS) and observed an asymmetric scattering pattern with respect to the qz-axis. The observed oriented morphology and texture hinder the diffusion of MAI molecules in the PbI2 films synthesized by vapor deposition, resulting in over 15% PbI2 remaining at the buried interface after reaction with MAI vapor. As a result, the MAPbI3 synthesized in this way was also highly oriented, especially in the surface layers. Surface fumigation (SF) step was introduced to decrease the orientational anisotropy of PbI2, which successfully breaks the diffusion barriers of MAI molecules by forming a complex layer on the PbI2 surface with polar solvent vapors, like dimethyl sulfoxide or 1,3-dimethyl-2-imidazolidinone. We infer that the SF treatment changes the vapor-solid reaction mechanism from reaction-crystallization to dissolution-recrystallization, which largely promotes the conversion of PbI2 to perovskite. Defects were reduced in perovskite synthesized in this way, and a p-i-n device with 19.56% efficiency was fabricated, which is among the highest efficiencies reported for sequential-vapor-deposited PSCs. Notably, this method enables the fabrication of conformal perovskite layers on uneven substrates. An exemplary PSC showing efficiency of 8.93% was fabricated on a precurved substrate. We believe that the method is applicable to the fabrication of tandem or curved PSCs that are compatible with wearable or building/autocar-integrated photovoltaics in the future.

Importance of methylammonium iodide partial pressure and evaporation onset for the growth of co-evaporated methylammonium lead iodide absorbers

Vacuum-based co-evaporation promises to bring perovskite solar cells to larger scales, but details of the film formation from the physical vapor phase are still underexplored. In this work, we investigate the growth of methylammonium lead iodide (MAPbI_3) absorbers prepared by co-evaporation of methylammonium iodide (MAI) and lead iodide (PbI_2) using an in situ X-ray diffraction setup. This setup allows us to characterize crystallization and phase evolution of the growing thin film. The total chamber pressure strongly increases during MAI evaporation. We therefore assume the total chamber pressure to be mainly built up by an MAI atmosphere during deposition and use it to control the MAI evaporation. At first, we optimize the MAI to PbI_2 impingement ratios by varying the MAI pressure at a constant PbI_2 flux rate. We find a strong dependence of the solar cell device performance on the chamber pressure achieving efficiencies > 14% in a simple n-i-p structure. On the road to further optimizing the processing conditions we vary the onset time of the PbI_2 and MAI deposition by delaying the start of the MAI evaporation by t = 0/8/16 min. This way, PbI_2 nucleates as a seed layer with a thickness of up to approximately 20 nm during this initial stage. Device performance benefits from these PbI_2 seed layers, which also induce strong preferential thin film orientation as evidenced by grazing incidence wide angle X-ray scattering (GIWAXS) measurements. Our insights into the growth of MAPbI_3 thin films from the physical vapor phase help to understand the film formation mechanisms and contribute to the further development of MAPbI_3 and related perovskite absorbers.

Rationalizing the enhancement of the thermoelectric properties of PEDOT:PSS by secondary doping

The enhancement of the thermoelectric (TE) properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) through secondary doping is well-known. In particular, the increase in the power factor (PF) following the addition of the strong polar solvent dimethyl sulfoxide (DMSO) in an aqueous solution is largely reported. However, systematic and comprehensive characterization of the morphological, compositional, and energetic evolution of the system with the addition of the secondary dopant is still missing. Here, the rationalization of the PF enhancement of PEDOT:PSS thin films with the addition of DMSO is presented. The system evolution is followed with morphological, by AFM and grazing incident wide angle x-ray scattering (GIWAXS), compositional, by x-ray photoelectron spectroscopy (XPS), and energetic, by ultraviolet photoelectron spectroscopy (UPS), measurements as varying the secondary dopant percentage from 0 to 50 vol. %. UPS measurements reveal no changes in the work function, substantiating the measured constant values of Seebeck coefficient (S) as varying the percentage of DMSO. On the other hand, XPS analysis confirms that the PSS to PEDOT ratio decreases with the addition of DMSO. However, the compositional changes do not influence the molecular packing and the thin film crystallinity, as reported by GIWAXS measurements. This comprehensive analysis of the system evolution makes possible to safely relate the increase in the electrical conductivity (σ) as a function of the secondary dopant to the sole enhancement of the charge carrier mobility, due to both morphological and chemical composition changes.

Deep Blue Fluorescent Material with an Extremely High Ratio of Horizontal Orientation to Enhance Light Outcoupling Efficiency (44%) and External Quantum Efficiency in Doped and Non-Doped Organic Light-Emitting Diodes

A novel bis-4Ph-substituted 9,10-dipehnylanthracene deep blue [1931 CIE (0.15, 0.08)] fluorescent compound, AnB4Ph, has been synthesized and characterized for organic light-emitting diode (OLED) applications. Our experimental study of AnB4Ph excludes the possibility of triplet-triplet annihilation, hybridized local and charge transfer, or thermally activated delayed fluorescent characteristics of the material. Since the solid-state photoluminescence quantum yield of AnB4Ph was determined to be 48%, assuming a 100% for the charge recombination efficiency, the light outcoupling efficiency (ηout) of an AnB4Ph non-doped OLED achieving an external quantum efficiency (EQE) of 5.3% is at least 44%, which is more than twofold higher than 20% for conventional OLEDs. Both grazing incidence wide-angle X-ray scattering (GIWAXS) and angle-dependent photoluminescence (ADPL) measurements reveal AnB4Ph having a high value of order parameter (SGIWAXS) of 0.61 for a ππ stacking along the normal direction and an orientation order parameter (SADPL) for a horizontal emitting dipole moment of -0.50 or Θ (horizontal-dipole ratios) of 100%, respectively. Otherwise, a refractive index (n) measurement provides a n = 1.80 for AnB4Ph thin films. Based on ηout = 1.2 × n-2, the calculated ηout is 37%, which is also in accordance with the results of GIWAXS and ADPL. We have also fabricated the classical fluorescent DPAVBi-doped AnB4Ph OLEDs, which display a true blue [1931 CIE (0.15 and 0.16)] electroluminescence with a high efficiency (EQE = 6.9%), surpassing the conventional ∼5% EQE. Based on an ηout of 42% for DPAVBi-doped AnB4Ph OLEDs, our studies suggest that the extremely horizontally aligned AnB4Ph host material exerts the same horizontal alignment on the DPAVBi dopant molecules.

Unveiling Crystal Orientation in Quasi-2D Perovskite Films by In Situ GIWAXS for High-Performance Photovoltaics.

Quasi-2D perovskites are enchanting alternative materials for solar cells due to their intrinsic stability. The manipulation of crystal orientation of quasi-2D perovskites is indispensable to target efficient devices, however, the origin of orientation during the film fabrication process still lacks in-depth understanding and convincing evidence yet, which hinders further boosting the performance of photovoltaic devices. Herein, the crystallizing processes during spin-coating and annealing are probed by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS), and the incident-angle-dependent GIWAXS is conducted to unveil the phase distribution in the films. It is found that undesirable lead iodide sol-gel formed intermediate phase would disturb oriented crystalline growth, resulting in random crystal orientation in poor quasi-2D films. A general strategy is developed via simple additive agent incorporation to suppress the formation of the intermediate phase. Accordingly, highly oriented perovskite films with reduced trap density and higher carrier mobility are obtained, which enables the demonstration of optimized quasi-2D perovskite solar cells with a power conversion efficiency of 15.2% as well as improved stability. This work paves a promising way to manipulate the quasi-2D perovskites nucleation and crystallization processes via tuning nucleation stage.

Regiochemistry-Driven Organic Electrochemical Transistor Performance Enhancement in Ethylene Glycol-Functionalized Polythiophenes.

Novel p-type semiconducting polymers that can facilitate ion penetration, and operate in accumulation mode are much desired in bioelectronics. Glycol side chains have proven to be an efficient method to increase bulk electrochemical doping and optimize aqueous swelling. One early polymer which exemplifies these design approaches was p(g2T-TT), employing a bithiophene-co-thienothiophene backbone with glycol side chains in the 3,3' positions of the bithiophene repeat unit. In this paper, the analogous regioisomeric polymer, namely pgBTTT, was synthesized by relocating the glycol side chains position on the bithiophene unit of p(g2T-TT) from the 3,3' to the 4,4' positions and compared with the original p(g2T-TT). By changing the regio-positioning of the side chains, the planarizing effects of the S-O interactions were redistributed along the backbone, and the influence on the polymer's microstructure organization was investigated using grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. The newly designed pgBTTT exhibited lower backbone disorder, closer π-stacking, and higher scattering intensity in both the in-plane and out-of-plane GIWAXS measurements. The effect of the improved planarity of pgBTTT manifested as higher hole mobility (μ) of 3.44 ± 0.13 cm2 V-1 s-1. Scanning tunneling microscopy (STM) was in agreement with the GIWAXS measurements and demonstrated, for the first time, that glycol side chains can also facilitate intermolecular interdigitation analogous to that of pBTTT. Electrochemical quartz crystal microbalance with dissipation of energy (eQCM-D) measurements revealed that pgBTTT maintains a more rigid structure than p(g2T-TT) during doping, minimizing molecular packing disruption and maintaining higher hole mobility in operation mode.

Structural and Trap‐State Density Enhancement in Flash Infrared Annealed Perovskite Layers

AbstractPerovskite solar cells are well‐known for their high energy conversion efficiency, low‐temperature processing, and cost‐effective production. Flash infrared annealing (FIRA) of slot‐die cast perovskite precursors offers an attractive manufacturing route using high‐throughput roll‐to‐roll technology. Despite the recent progress in FIRA perovskite annealing, the optimal composition of the perovskite precursor is yet to be developed. Here, the effect of methylammonium chloride (MACl) on the perovskite structure and trap‐state density as a function of the FIRA annealing time is investigated. In situ real‐time grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) is employed to monitor the perovskite layer formation during FIRA annealing with millisecond temporal resolution. In addition, the density of states in the bandgap is estimated using ex situ energy‐resolved electrochemical impedance spectroscopy. Evidence is found that adding 10% MACl into the perovskite precursor solution significantly improves the crystallographic orientation of the perovskite layers while reducing the trap‐state density by one order of magnitude. In addition, using time‐resolved GIWAXS, the most favorable time window for the FIRA processing of perovskite films with the lowest mosaicity and trap‐state density is identified. The results are of general importance for elucidating the appropriate temporal windows in complex and fast‐evolving crystallization processes.