Two-dimensional Grazing Incidence X-ray Diffraction Research Articles

Critical Role of Non-Halogenated Solvent Additives in Eco-Friendly and Efficient All-Polymer Solar Cells.

Organic solar cells (OSCs) demonstrating high power conversion efficiencies have been mostly fabricated using halogenated solvents, which are highly toxic and harmful to humans and the environment. Recently, non-halogenated solvents have emerged as a potential alternative. However, there has been limited success in attaining an optimal morphology when non-halogenated solvents (typically o-xylene (XY)) were used. To address this issue, we studied the dependence of the photovoltaic properties of all-polymer solar cells (APSCs) on various high-boiling-point non-halogenated additives. We synthesized PTB7-Th and PNDI2HD-T polymers that are soluble in XY and fabricated PTB7-Th:PNDI2HD-T-based APSCs using XY with five additives: 1,2,4-trimethylbenzene (TMB), indane (IN), tetralin (TN), diphenyl ether (DPE), and dibenzyl ether (DBE). The photovoltaic performance was determined in the following order: XY + IN < XY + TMB < XY + DBE ≤ XY only < XY + DPE < XY + TN. Interestingly, all APSCs processed with an XY solvent system had better photovoltaic properties than APSCs processed with chloroform solution containing 1,8-diiodooctane (CF + DIO). The key reasons for these differences were unraveled using transient photovoltage and two-dimensional grazing incidence X-ray diffraction experiments. The charge lifetimes of APSCs based on XY + TN and XY + DPE were the longest, and their long lifetime was strongly associated with the polymer blend film morphology; the polymer domain sizes were in the nanoscale range, and the blend film surfaces were smoother, as the PTB7-Th polymer domains assumed an untangled, evenly distributed, and internetworked morphology. Our results demonstrate that the use of an additive with an optimal boiling point facilitates the development of polymer blends with a favorable morphology and can contribute to the widespread use of eco-friendly APSCs.

In situ observations of graphene growth and strong graphene‑nickel interactions by grazing incidence X-ray diffraction

The growth mechanisms of graphene on polycrystalline Ni by chemical vapor deposition using polymethyl methacrylate (PMMA) as solid-state carbon sources were investigated by in-situ two-dimensional grazing incidence X-ray diffraction (GIXRD). The results show that the formation of graphene can be described by four stages: The graphitization of solid-state carbon, carbon dissolution in Ni, graphene nucleation, and isothermal growth of graphene, suggesting that the graphitization mechanism is metal-induced crystallization (MIC) mechanism. The so-called induction is mutual, that is, Ni induces the growth of graphene, and reciprocally, graphene induces the rotation and reorientation of Ni. The reorientation of Ni is the enhancement of Ni(111). The rotation and reorientation of Ni occur simultaneously with the nucleation of graphene and continue throughout the growth of graphene. The rotation of Ni ends when the graphene growth stops. Further, the forces causing the rotation and reorientation of the surface Ni lattice are analyzed. It was discovered for the first time that grain rotation was caused by directional carbon diffusion and graphene-Ni interaction. In addition, when the growth temperature is the same, the time when graphene starts to grow is mainly related to the nickel matrix but not the carbon source.

In situ observation of metal ion interactions with graphene oxide layers: From the growth of metal hydroxide to metal oxide formation

The interactions between metal ions and graphene oxide (GO) nanosheets were investigated by in situ two-dimensional grazing incidence X-ray diffraction (GIXRD). We found that metal cations (Mn2+, Co2+, Cu2+, Fe3+) and GO can self-assemble into a hydroxide/GO superlattice by drop-casting a metal chloride and GO solution due to the electrostatic interactions between the positively charged hydroxide and the negatively charged GO nanosheets and the interlayer spacing of the superlattice can be controlled by the cation species. Moreover, based on this superlattice template, graphene-based metal oxide nanosheets can be facilely obtained by subsequent annealing. The growth mechanism and structural evolution of the GO/cation systems can be described in four stages: (1) hydrated cation intercalation of the GO interlayer in an aqueous solution; (2) metal hydroxide growth between the GO layers during annealing, with the formation of a superlattice structure at approximately 250 °C; (3) metal oxide nucleation between the reduced GO (rGO) interlayers with increasing temperature; and (4) complete graphene layer decomposition at a temperature of 600 °C, along with metal oxide nanosheet formation. This work gives a new perspective for understanding the interactions between and growth behaviour of metal cations and GO.

To Reveal the Importance of the Crystallization Sequence on Micro-Morphological Structures of All-Crystalline Polymer Blends by In Situ Investigation.

In crystalline/crystalline polymer blend systems, complex competition and coupling of crystallization and morphology usually happen due to the different crystal nucleation and growth processes of polymers, making the morphology and crystallization behavior difficult to control. Herein, we probe the crystallization sequence during the film formation process (crystallize simultaneously, component A crystallizes prior to B or inverse) to illustrate the micro-morphology evolution process in poly(3-hexylthiophene) (P3HT) and poly[[N,N-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-5, 5'-(2,2'-bithiophene)] (N2200) blend using in situ UV-vis absorption spectra and in situ two-dimensional grazing incidence X-ray diffraction (2D GIXRD). When P3HT and N2200 crystallize simultaneously, a large-sized morphology structure is formed. When strengthening the solution aggregation of P3HT by increasing the solvent-polymer interaction, P3HT crystallizes prior to N2200. A P3HT-based micro-morphology structure is obtained. As the molecular weight of N2200 increases to a critical value (72.0 kDa), the crystallization of N2200 dominates the film formation process. A N2200-based micro-morphology is formed guided by N2200 domains. The results confirm that the crystallization sequence is one of the most important factors to determine the micro-morphology structure in all-crystalline polymer blends.

Modulation of perovskite crystallization processes towards highly efficient and stable perovskite solar cells with MXene quantum dot-modified SnO2

MQDs-SnO2-modulated perovskite crystallization processes visualized by in situ 2D GIXRD technique.

Orientation Control of Semiconducting Polymers Using Microchannel Molds

The molecular orientation of organic semiconductors (OSCs) is of fundamental importance to anisotropic electrical behavior as well as superior properties in practical applications. Here, a simple and effective method is demonstrated to fabricate highly oriented semiconducting polymers, poly(3-hexylthiophene) (P3HT) and poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)), by mass transfer effect under microchannel molds by diffusion and convection. Furthermore, parallel or perpendicular molecular arrangements relative to the channel direction were achieved by varying the widths of the microchannels, which are directly observed using polarized optical microscopy and two-dimensional grazing-incidence X-ray diffraction experiments. The method could enable the fabrication of organic field-effect transistors that exhibit anisotropic electrical properties indicating inter- or intrachain charge transport. The resulting platform will provide a simple approach for multidirectional orientations of anisotropic OSCs.

Templating effect of single-layer graphene supported by an insulating substrate on the molecular orientation of lead phthalocyanine.

The influence of single-layer graphene on top of a SiO2/Si surface on the orientation of nonplanar lead phthalocyanine (PbPc) molecules is studied using two-dimensional grazing incidence X-ray diffraction. The studies indicate the formation of a mixture of polymorphs, i.e., monoclinic and triclinic forms of PbPc with face-on (lying down) and edge-on (standing up) PbPc orientations, respectively. The formation of monoclinic fractions is attributed to the presence of the graphene layer directing the π interactions between the highly delocalized macrocycles. The competing interfacial van der Waals forces and molecule–molecule interactions lead to the formation of a small fraction of triclinic moieties. The nanoscale electrical characterization of the thin PbPc layer on graphene by means of conducting atomic force microscopy shows enhanced vertical conductance with interconnected conducting domains consisting of ordered monoclinic crystallites through which the charge transfer occurs via tunneling. These results show the importance of a templating layer to induce the formation of a required phase of PbPc suitable for specific device applications.

Highly Efficient and Air Stable Ternary Organic Solar Cell Enabled By Employing a Perylenediimide-Based Acceptor

Organic solar cells (OSCs) are regarded as one of the promising photovoltaic technologies to address the issues of energy crisis and environmental pollution all over the world, and are thus considered as the next generation of solar cells. 1 However, the devices power conversation efficiency and stability of the devices are still important factors to limit the commercial application of OSCs. 2 To this end, enhancement of photon absorption is an attractive strategy for the increase of PCE. Recently, developing the ternary OSCs with three materials of complementary absorption spectra is an efficient method to enhance the photon harvesting of single junction devices while having a fairly simple fabrication process. Meanwhile, the morphology of active layers can be finely optimized by selecting the third component and adjusting its contents to improve performance of ternary OSCs. 3 Herein, we synthesized highly air-stable perylenediimide (PDI)-based non-fullerene material and integrated it into common organic solar cells as the third component to form the ternary OSCs. This cascade band structure showed a better energy level alignment and the complimentary absorption, thus demonstrating a high ternary device efficiency of 8.71% that represented 14.6% enhancement with respect to the corresponding binary OSCs. Besides, morphology was characterized by two-dimensional grazing-incidence X-ray diffraction (2D-GIXRD) and photo-induced force microscopy (PiFM) and results suggest improved compatibility between organic materials in OSCs, which could reduce the electronic trap states to inhibit the charge recombination and increase the stability of devices. The ternary OSCs thus exhibited good air stability, photo-stability and humidity. Our work provides a very promising approach to enhance the photovoltaic performance while demonstrating highly stable devices, which could contribute to the future development of the large area manufacturing in an ambient condition and roll-to roll processing on flexible substrates. Reference 1. Yu T., Xu X. P., Zhang G. J., Wan J. H., Li Y., Peng Q., advanced functional materials, 2017, 1701491.2. Li P. D., Mainville M., Zhang Y. L., leclerc M., Sun B. Q., Izquierdo R., Ma D. L., small, 2019, 1804671.3. An Q. S., Zhang F. J., Gao w., Sun Q. Q., Zhang M., Yang C. L., Zhang J., nano energy, 2018, 45, 177-183.

Effect of Backbone Sequence of a Naphthalene Diimide-Based Copolymer on Performance in n-Type Organic Thin-Film Transistors.

We report two newly synthesized naphthalene diimide (NDI)-based conjugated polymers, poly[(E)-2,7-bis(2-decyltetradecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone-vinylene-thiophene-vinylene] (PNDI-VTV) and poly[(E)-2,7-bis(2-decyltetradecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone-vinylene-selenophene-vinylene] (PNDI-VSV) with different donor units as electron-transporting organic semiconductors for organic field-effect transistors (OFETs). Furthermore, we study the effect of vinylene position on electron transport in the NDI polymers by using two similar polymers but with thiophene-vinylene-thiophene (PNDI-TVT) instead of vinylene-thiophene-vinylene or selenophene-vinylene-selenophene (PNDI-SVS) instead of vinylene-selenophene-vinylene. By incorporating vinylene between thiophene (or selenophene) units, the resulting NDI-based polymers PNDI-VTV and PNDI-VSV show larger backbone planarity than PNDI-TVT and PNDI-SVS. The polymers with a shorter acceptor monomer unit (PNDI-VTV and PNDI-VSV) show a strong face-on orientation, whereas those with a longer monomer unit (PNDI-TVT and SVS) exhibit a mixed face-on and edge-on orientation by two-dimensional grazing incidence X-ray diffraction. Optimized PNDI-VTV and PNDI-VSV OFETs exhibit electron mobilities of 0.043 and 0.7 cm2/(V·s), which is quite lower than those of PNDI-TVT and PNDI-SVS. In addition, the activation energies for electron transport of PNDI-VTV and PNDI-VSV were larger than those of PNDI-TVT and PNDI-SVS. Overall, this research provides the insight that the molecular alignment on the substrate can be controlled by the sequence of rigid acceptor monomer molecules for improving the electron transport of NDI polymers.

Cone-jet printing of aligned silver nanowire/poly(ethylene oxide) composite electrodes for organic thin-film transistors

Abstract Aligned silver nanowire (AgNWs) conductive electrodes are printed through an electrohydrodynamic (EHD) jet printing via cone-jet mode. We investigate effects of poly(ethylene oxide) (PEO) addition to AgNW inks in terms of surface energy, ink viscosity, and electrical conductivity. The optimized PEO content in the ink is determined to be ∼10 wt%, at which well-defined AgNWs/PEO composite electrodes aligned along the printing direction can be prepared by cone-jet mode of EHD jet printing. We fabricate bottom contact organic thin film transistors (OTFTs) with TIPS-pentacene/PS blend as a semiconducting layer to take advantage of printed AgNWs/PEO electrodes. The resulting devices exhibit stable transfer characteristics for 12 h even in ambient air with average field-effect mobility (μFET), threshold voltage (Vth) and on/off current ratio (Ion/Ioff) of 0.51 cm2/V, −2.0 V, and ∼106, respectively. To understand the characteristics of OTFTs based on AgNWs/PEO composite electrodes in detail, we examine crystalline morphology and molecular orientation of TIPS-pentacene/PS blend on various substrates through field emission scanning electron microscopy and two-dimensional grazing incidence X-ray diffraction, respectively.

Alternative Face-on Thin Film Structure of Pentacene

Pentacene attracts a great deal of attention as a basic material used in organic thin-film transistors for many years. Pentacene is known to form a highly ordered structure in a thin film, in which the molecular long axis aligns perpendicularly to the substrate surface, i.e., end-on orientation. On the other hand, the face-on oriented thin film, where the molecular plane is parallel to the substrate, has never been found on an inert substrate represented by SiO2. As a result, the face-on orientation has long been believed to be generated only on specific substrates such as a metal single crystal. In the present study, the face-on orientation grown on a SiO2 surface has first been identified by means of visible and infrared p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) together with two-dimensional grazing incidence X-ray diffraction (2D-GIXD). The combination of the multiple techniques readily reveals that the face-on phase is definitely realized as the dominant component. The face-on film is obtained when the film growth is kinetically restricted to be prevented from transforming into the thermodynamically stable structure, i.e., the end-on orientation. This concept is useful for controlling the molecular orientation in general organic semiconductor thin films.

Molecular Orientation Change in Naphthalene Diimide Thin Films Induced by Removal of Thermally Cleavable Substituents

The potential of naphthalene-1,8:4,5-tetracarboxylic diimide (NDI-H) as a transparent electron-transporting material was examined. A soluble precursor was designed and synthesized having two tert-butoxycarbonyl solubilizing substituents at the imide moieties. This precursor molecule, NDI-Boc, is converted to the hydrogen-substituted NDI-H by heating the spin-coated precursor films. The molecular orientation during the thermal conversion of NDI-Boc to NDI-H was examined using two-dimensional grazing incidence X-ray diffraction (2D-GIXD) and p-polarized multiple-angle incidence resolution spectrometry. It was revealed that, driven by the formation of intermolecular hydrogen bonds, the molecular orientation changes from tilted edge-on to face-on orientation. In situ 2D-GIXD measurements confirmed that the change of molecular orientation is simultaneously caused by the cleaving of the Boc substituents. Time-resolved microwave conductivity measurements were used to show that the resulting NDI-H film has anisot...

Current mapping of lead phthalocyanine thin films in the presence of gaseous dopants.

The structural organization and its effect on conducting pathways in lead phthalocyanine (PbPc) thin films, a nonplanar phthalocyanine, deposited on Si and highly oriented pyrolytic graphite (HOPG) substrates in the presence of iodine and ammonia vapors are presented. Two-dimensional grazing incidence X-ray diffraction studies reveal that the crystalline ordering in pristine PbPc films on Si and HOPG substrates undergoes a drastic molecular rearrangement and surface reconstruction upon iodine doping. The structural rearrangement leads to morphological changes and higher surface roughness in iodine doped PbPc (I-PbPc) films. The obvious enhancement in the current values of I-PbPc is attributed to the introduction of holes as charge carriers. Nanoscale current mapping reveals the presence of percolation pathways in I-PbPc films, on both Si and HOPG substrates, being responsible for the observed high conductance in contrast to the isolated conducting domains in the pristine PbPc system. The broad distribution of current values across various conducting domains on Si is attributed to a mixture of crystalline phases and disordered fractions of I-PbPc, while the narrow distribution of current values observed in the case of HOPG arises from the majorly disordered PbPc molecules. These films also show enhanced sensitivity towards ammonia that is almost four times higher in magnitude than for pristine PbPc films. The current maps show that the adsorption of ammonia molecules disrupts the iodine percolation pathways, thereby imposing a detrimental effect on the conductivity of the PbPc films.

Synthesis and Physicochemical Properties of Dibenzo[2,3- d:2',3'- d']anthra[1,2- b:5,6- b']dithiophene (DBADT) and Its Derivatives: Effect of Substituents on Their Molecular Orientation and Transistor Properties.

We have synthesized dibenzo[2,3- d:2',3'- d']anthra[1,2- b:5,6- b']dithiophene (DBADT) and several derivatives bearing alkyl and phenyl groups at various positions. The optical and electrochemical properties of the synthesized compounds were investigated. All the fabricated OFET devices exhibited typical p-type behavior under ambient conditions, and diphenyl-substituted analogue-based OFET devices showed excellent mobility, as high as 0.66 cm2 V-1 s-1. The surface morphology and molecular orientation in thin films were also investigated using atomic force microscopy (AFM) and two-dimensional grazing incidence X-ray diffraction (2D-GIXD). It was found that the substituents and their positions affect the molecular orbitals, molecular orientation, and morphology of the thin films, producing different FET performance.

Preferential Orientation of Tetrahedral Silicon-Based Hosts in Phosphorescent Organic Light-Emitting Diodes.

Vacuum-processed diphenylbis(3-(pyridine-2-yl)phenyl)silane (2PTPS), diphenylbis(3-(pyridine-3-yl)phenyl)silane (3PTPS), and diphenylbis(3-(pyridine-4-yl)phenyl)silane (4PTPS) have been used as electron-transporting host materials combined with tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as the hole-transporting host, which induce balanced charge carrier transport for high-efficiency phosphorescent organic light-emitting diodes. The 4PTPS-based organic light-emitting diodes with tris[2-phenylpyridinato-C2,N]iridium(III) [Ir(ppy)3] dopant showed highest current efficiency and external quantum efficiency of 53.54 cd/A and 15.61%, compared to 2PTPS (40.75 cd/A, 11.84%) and 3PTPS (29.35 cd/A, 8.54%). These results were attributed to the well-aligned structure with preferential horizontal orientation of the emitting material layer by the diffraction intensity distribution as a function of azimuthal angle in two-dimensional grazing incidence X-ray diffraction analysis. The molecular orientation of TCTA:4PTPS material with a narrow azimuthal intensity distribution had better priority to the horizontal direction than the other TCTA:2PTPS and TCTA:3PTPS materials, which is related to the charge transport as well as the device efficiency. We found that the preferential horizontal orientation of the co-host material with a balanced charge carrier was not affected by Ir(ppy)3 dopant with a homoleptic structure and bis-[2-(4,6-difluorophenyl)pyridinato-N,C2](picolinato)iridium [Firpic] dopant with a heteroleptic structure in the co-host/dopant system.

Surface crystallographic structures of cellulose nanofiber films and overlayers of pentacene

Cellulose nanofibers or nanocellulose is a promising recently developed biomass and biodegradable material used for various applications. In order to utilize this material as a substrate in organic electronic devices, thorough understanding of the crystallographic structures of the surfaces of the nanocellulose composites and of their interfaces with organic semiconductor molecules is essential. In this work, surface crystallographic structures of nanocellulose films (NCFs) and overlayers of pentacene were investigated by two-dimensional grazing-incidence X-ray diffraction. The NCFs are found to crystallize on solid surfaces with the crystal lattice preserving the same structure of the known bulk phase, whereas distortion of interchain packing toward the surface normal direction is suggested. The pentacene overlayers on the NCFs are found to form the thin-film phase with an in-plane mean crystallite size of over 10 nm.

Synthesis and Characterization of Polycyclic Aromatic Hydrocarbons with Different Spatial Constructions Based on Hexaphenylbenzene Derivatives.

In recent years, low-bandgap polymers have attracted much attention in a wide range of fields. The synthesis of these compounds has been focused on three factors according to the Roncali bandgap theory: 1) the degree of bond-length alternation (Eδr ), 2) the aromatic resonance energy of the cycle (ERes ), and 3) the substituted groups (ESub ). Herein, we have designed and prepared low-bandgap polymers in a different way by using the factors Eθ (the deviation from planarity of the polymer chain) and EInt (the interaction of the molecular chains in the solid state). Thus, three polycyclic aromatic hydrocarbons with different spatial constructions, based on hexaphenylbenzene derivatives, were prepared in this work: linear (P1-OX), V (P2-OX), and zigzag (P3-OX) types. These well-defined polymers exhibited interesting optical and electrochemistry behavior due to their different extents of planarity. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry gave the incremental orderly molecular weight distributions of P1, P2, and P3, the weight-average molecular weights (M‾w ) of which were 9000, 5500, and 69 000, respectively. Their lamellar layer structures and π-π intermolecular stacking were demonstrated by using two-dimensional grazing-incidence X-ray diffraction, which revealed the edge-on chain conformation. Finally, the materials were perfectly adapted to fabricate high-performance organic field-effect transistor devices, which revealed that these compounds could have great prospects as semiconductors.

Fluorinated Dithienylethene–Naphthalenediimide Copolymers for High-Mobility n-Channel Field-Effect Transistors

We develop two donor–acceptor copolymers based on a fluorinated dithienylethene building block, namely PNFDTE1 and PNFDTE2, in which naphthalenediimide (NDI) acts as an acceptor unit. Thermogravimetric analysis displayed both copolymers having good thermal stability with high decomposition temperatures over 400 °C. Broad absorption spectra were observed in the UV–vis–NIR region, with the absorption maxima being 720 and 724 nm for PNFDTE1 and PNFDTE2, respectively. Cyclic voltammetry tests exhibited deep-lying lowest unoccupied molecular orbital energy levels of ca. −4.0 eV. Two-dimensional grazing incidence X-ray diffraction patterns showed that different packing modes for two polymers result in the variation in charge transport properties. Backbone fluorination effectively decreases electron injection barrier, thereby facilitating electron mobility. An impressive electron mobility of 3.20 cm2 V–1 s–1 was achieved in air for PNFDTE1-based polymer field-effect transistors fabricated on the poly(ethylene te...

Development of Novel Conjugated Polyelectrolytes as Water-Processable Interlayer Materials for High-Performance Organic Photodiodes

A series of novel conjugated polyelectrolytes composed of two different building blocks with different composition ratios were designed and synthesized for application as a functional layer in high-performance organic photodiodes (OPDs). A homopolymer and two random copolymers were prepared using different molar ratios of dibromo 1,4-bis(4-sulfonatobutoxy)benzene (SPh) and dibromo 1,4-bis(4-tetraethylene glycol)benzene (EGPh): EG20 with SPh:EGPh ratio of 0.8:0.2 and EG40 with a ratio of 0.6:0.4. Structural analyses by two-dimensional grazing-incidence X-ray diffraction and near-edge X-ray absorption fine structure spectroscopy studies proved that a higher EGPh content could induce more organized polymer chains with face-on orientation of EG20 and EG40. Such an orientation of EG20 and EG40 along with the ordered crystalline organization yielded effective molecular dipole moments in the thin films when applied as an interlayer between ZnO and an active layer of inverted OPDs. As confirmed by ultraviolet pho...

Following the TRMC Trail: Optimization of Photovoltaic Efficiency and Structure-Property Correlation of Thiophene Oligomers.

Semiconducting conjugated oligomers having same end group (N-ethylrhodanine) but different central core (thiophene: OT-T, bithiophene: OT-BT, thienothiophene: OT-TT) connected through thiophene pi-linker (alkylated terthiophene) were synthesized for solution processable bulk-heterojunction solar cells. The effect of the incorporation of an extra thiophene to the central thiophene unit either through C-C bond linkage to form bithiophene or by fusing two thiophenes together to form thienothiophene on the optoelectronic properties and photovoltaic performances of the oligomers were studied in detail. Flash photolysis time-resolved microwave conductivity (FP-TRMC) technique shows OT-TT has significantly higher photoconductivity than OT-T and OT-BT implying that the former can outperform the latter two derivatives by a wide margin under identical conditions in a bulk-heterojunction solar cell device. However, the initial photovoltaic devices fabricated from all three oligomers (with PC71BM as the acceptor) gave power conversion efficiencies (PCEs) of about 0.7%, which was counterintuitive to the TRMC observation. By using TRMC results as a guiding tool, solution engineering was carried out; no remarkable changes were seen in the PCE of OT-T and OT-BT. On the other hand, 5-fold enhancement in the device efficiency was achieved in OT-TT (PCE: 3.52%, VOC: 0.80 V, JSC: 8.74 mA cm(-2), FF: 0.50), which was in correlation with the TRMC results. The structure-property correlation and the fundamental reasons for the improvement in device performance upon solvent engineering were deduced through UV-vis absorption, atomic force microscopy, bright-field transmission electron microscopy, photoluminescence quenching analysis and two-dimensional grazing incidence X-ray diffraction studies.