Understanding the microstructures of semiconducting polymers is critical for improving the charge transport properties of polymer field-effect transistors (PFETs). A series of diketopyrrolopyrrole-based copolymers designed by implementing the concept of intramolecular noncovalent conformational locks through the functionalization of polymer backbones with fluorine atoms or methoxy groups were synthesized and compared with their unfunctionalized analogue. In contrast to the bimodal texture of the unfunctionalized polymer, the thin films of the polymer with fluorine atoms exhibit predominantly edge-on texture with much improved crystalline ordering. The thin films of the polymer modified with methoxy groups have a principally face-on texture. These dramatic differences in thin-film texture can be correlated with the polymers’ solubilities. Furthermore, the improved crystalline ordering of these semiconductor polymers enables the fabrication of high-performance PFETs: the hole mobility of the methoxy-modified polymer is reduced by half with respect to that of the unmodified polymer, whereas the hole mobility values of the fluorine-modified polymer are up to ∼6 times higher, approximately 1.32 cm2 V–1 s–1, and exhibit pronounced thermal stability. These results provide new guidelines for the molecular design of semiconducting polymers with noncovalent conformational locks.

Organometal halide perovskite solar cells (PeSCs) are regarded as promising photovoltaics due to their outstanding power conversion efficiencies (PCEs). However, even though their PCEs are achieved over 20%, their intrinsically poor stability is a big bottleneck for their practical uses. Here, a simple method is reported using phenyl‐C61‐butyric acid methyl ester as a molecular additive to improve thermal stability of organometal halide perovskite crystals, which also improves the PCEs of the associated PeSCs. Moreover, by varying the grain size of perovskite crystals up to ≈150 µm, it is demonstrated that grain boundary plays a significant role in their thermal stability. Cells with smaller grain interface area (i.e., larger grain size) have higher thermal stability. The additive is located at grain boundaries and found to induce electron transfer reactions with halogens in the perovskite. The reaction products chemically passivate perovskite crystals and strongly bind halogen atoms at grain boundaries to their crystal lattice, preventing them from exiting from the crystal lattice, which improves thermal stability of perovskite crystals. This study offers a simple method for improving thermal stability of perovskite without any loss and opens up the possibility of the use of various molecular additives to achieve highly stable PeSCs.

This study presents an effective guide to vertical phase separation of polymer–fullerene blends based on systematic comparison of compatibility, crystallization, and processing conditions in observing the vertical morphology.

We fabricated hybrid poly­(3-hexylthiophene) nanofibers (P3HT NFs) with rigid backbone organization through the self-assembly of P3HT tethered to gold NPs (P3HT-Au NPs) in an azeotropic mixture of tetrahydrofuran and chloroform. We found that the rigidity of the P3HT chains derives from the tethering of the P3HT chains to the Au NPs and the control of the solubility of P3HT in the solvent. This unique nanostructure of hybrid P3HT NFs self-assembled in an azeotropic mixture exhibits significantly increased delocalization of singlet (S1) excitons compared to those of pristine and hybrid P3HT NFs self-assembled in a poor solvent for P3HT. This strategy for the self-assembly of P3HT-Au NPs that generate long-lived S1 excitons can also be applied to other crystalline conjugated polymers and NPs in various solvents and thus enables improvements in the efficiency of optoelectronic devices.

research has been successfully conducted to optimize the BHJ-based OPV devices, including the development of new photoactive materials, [11][12][13][14] pre or postproduction treatment methods, [15][16][17][18] and device architectures. [19][20][21][22][23][24][25][26][27][28][29] Especially, in the area of the device architecture optimization, tremendous efforts have been dedicated toward optimizing the electrode interfaces by adjusting the optical modulus [ 19 ] and promoting effi cient charge collection through Ohmic contacts. [30][31][32][33][34][35] Several reports have focused on the "carrier selectivity" at electrodes, which critically determines the photovoltaic performance of devices with non-Ohmic contact electrodes, such as inverted OPVs. [36][37][38] Since the difference in the work functions (WFs) of electrodes is usually not suffi cient to constitute the built-in potential within an inverted OPV device incorporating high work function cathodes such as the Indium Tin Oxide (ITO), the effi cient charge collection in BHJ structures, which bears an intrinsically high probability of unwanted charge recombination near the electrode, must be sought through approaches that block misdirected carriers at the electrode interface. [ 39 ] In this sense, wide bandgap semiconductor materials, such as ZnO, TiO x , MoO 3 , and their composites, have been widely studied as carrier selective layers. [40][41][42][43] However, the complexities of polymer-based blend systems and the indistinct interfaces in the multilayer structures hinder a comprehensive investigation of the charge-collecting interfaces outside of traditional empirical approaches in the respective photoactive layers. Therefore, the development of new device architectures that enable explicit control over the interfaces, as well as an improved understanding of the corresponding device operating mechanism, should be addressed before device performances may be further enhanced.Ferroelectric materials provide an interesting new strategy for precisely controlling the electrical properties of electronic devices. Inorganic ferroelectric materials, such as BiFeO 3 and NaNbO 3 , are frequently introduced to fabricate switchable fi eld-effect photovoltaic devices that enable control over the photovoltage above the bandgap, according to the polarization Interfacial energetics determines the performance of organic photovoltaic (OPV) cells based on a thin fi lm of organic semiconductor blends. Here, an approach to modulating the "carrier selectivity" at the charge collecting interfaces and the consequent variations in the nongeminate charge carrier recombination dynamics in OPV devices are demonstrated. A ferroelectric blend interfacial layer composed of a solution-processable ferroelectric poly mer and a wide bandgap semiconductor is introduced as a tunable electron selective layer in inverted OPV devices with non-Ohmic contact electrodes. The direct rendering of dipole alignment within the ferroelectric blend layer is found to increase the carrier selectivity of t...

We performed a kinetic analysis of the sequential deposition method (SDM) to investigate how to form perovskite (CH 3 NH 3 PbI 3 ) phases, and the effects of processing conditions on the final perovskite morphology. The reaction was found to consist of two periods with distinct kinetics. During the first period, perovskite crystals nucleated on the lead iodide (PbI 2 ) surface, and the reaction proceeded until the surface was completely converted to perovskites. The reaction during this period determined the surface morphology of the perovskites. We were able to extract the value of the rate of the phase transformation during the first period by applying the Johnson−Mehl−Avrami−Kolmogorov model, in which the rate r is related to the average grain size R by R ∝ r −1/3 . In this way, r was used to predict the surface morphology of the perovskite under certain processing conditions. During the second period, the remaining lead iodide under the top perovskite layer was converted. Methylammonium iodide (CH 3 NH 3 I, MAI) molecules apparently diffused into the buried PbI 2 through intergrain gaps of the top perovskite layers. Added MAI molecules reacted with PbI 2 but also generated single-crystal perovskite nanorods, nanoplates, and nanocubes. The current study has furthered the understanding of detailed features of the SDM, enabled a reliable prediction of the final perovskite morphology resulting from specified processing conditions, and contributed to a reproducible fabrication of high-quality perovskite films.

Two donor-acceptor copolymers, PBDT and PNDT, containing 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:3,4-b']dithiophene (BDT) and 4,9-bis(2-ethylhexyloxy)naphtho[1,2-b:5,6-b']dithiophene (NDT), respectively, as an electron-rich unit and 5,6-difluoro-2,1,3-benzothiadiazole (2FBT) as an electron-deficient unit, were synthesized and compared. The introduction of the NDT core into the conjugated backbone was found to effectively improve both light harvesting and the charge carrier mobility by enhancing chain planarity and backbone linearity; the NDT copolymer has stronger noncovalent interactions and smaller bond angles than those of the BDT-based polymer. Moreover, the introduction of the NDT core brings about a drastic change in the molecular orientation into the face-on motif and results in polymer:PCBM blend films with well-mixed interpenetrating nanofibrillar bulk-heterojunction networks with small-scale phase separation, which produce solar cells with higher short-circuit current density and fill factor values. A conventional optimized device structure containing PNDT:PC71BM was found to exhibit a maximum solar efficiency of 6.35%, an open-circuit voltage of 0.84 V, a short-circuit current density of 11.92 mA cm(-2), and a fill factor of 63.5% with thermal annealing, which demonstrates that the NDT and DT2FBT moieties are a promising electron-donor/acceptor combination for high-performance photovoltaics.

Mixed-halide perovskites, CH 3 NH 3 PbI 3−x Cl x , can be used to fabricate highly efficient perovskite solar cells; the presence of chlorine ions affects the perovskite morphology and enhances optoelectronic properties. However, the reported device performances of mixed-halide perovskites are comparable to those of triiodide perovskites, CH 3 NH 3 PbI 3 . Thus, the benefits of the presence of Cl − ions in mixed-halide perovskites are uncertain. To clarify the effects of Cl − on the optoelectronic properties of perovskite devices, a suitable device structure is required. In this study, lateral-structured perovskite devices are fabricated and their electrical properties are investigated. A clear contrast is found between the optoelectronic properties of the mixed-halide and triiodide perovskite; a suitable platform is also constructed for the spectroscopic analysis. Scanning photocurrent spectroscopy is used to visualize the charge carrier diffusion in the perovskite films and it is found that the charge carrier diffusion length of the mixed-halide perovskite is longer. It is also demonstrated by using conducting atomic force microscopy that the charge carrier pathways in the mixed-halide perovskite are more efficient, which means that it has longer charge carrier recombination life-times and higher photocurrents. This lateral-structured device has an architecture that makes it suitable for the observation of charge carrier diffusion and spectroscopic analysis.