La fundación de la Madrasa al-Adāb por la Asociación de ulemas musulmanes argelinos en la ciudad de Hennaya (Tremecén) en 1950

A biphenyl-fused BODIPY was synthesized through a facile oxidative cyclization of peripheral aryl-substituents at the β-position of the BODIPY unit. The extended π-system of the fused BODIPY induces near-infrared (NIR) absorption and strong π–π interactions in the solid state. These features are beneficial for the application of the dye as a functional material. The biphenyl-fused BODIPY dye was demonstrated to exhibit photocurrent conversion ability on the basis of its <i>n</i>-type semiconducting property

Hole Relaxation in Polymer:Fullerene Solar Cells Examined by the Simultaneous Measurement of Time-of-Flight and Time-Resolved Microwave Conductivity

To comprehensively examine charge carrier transport and relaxation, we report a new technique combining time-of-flight (TOF) and time-resolved microwave conductivity (TRMC) using a harmonic cavity. The TOF analysis affords long-range hole mobilities of 10^–4–10^–2 cm² V^–1 s^–1 for polymer:methanofullerene bulk heterojunction (BHJ) films (P3HT, PffBT4T, and PCPDTBT blended with PCBM), while TRMC transients are simultaneously recorded under an external electric field. The latter exhibits the acceleration of decay with increasing bias voltage. By analyzing the transient photocurrents and TRMC decays based on a diffusion theory with bulk charge recombination, hole relaxation is observed as a function of time (nanoseconds to microseconds) or distance (∼micrometers). Contrasting results are found among the BHJ films, which are consistent with the optimal thickness of the organic solar cells and provide the basis to interpret charge carrier dynamics from the spatiotemporal viewpoint

Spatial Inhomogeneity of Methylammonium Lead-Mixed Halide Perovskite Examined by Space- and Time-Resolved Microwave Conductivity

Reducing the spatial inhomogeneity of solution-processed, multicrystalline methylammonium lead iodide (MAPbI₃) perovskite is of great importance for improving its power conversion efficiency, suppressing point-to-point deviations, and delaying degradation during operation. Various techniques, such as conducting-mode atomic force microscopy and photoluminescence mapping, have been applied for this intriguing class of materials, revealing nonuniform electronic properties on the nanometer-to-micrometer scale. Here, we designed a new space- and time-resolved microwave conductivity system that enables mapping of the transient photoconductivity with resolution greater than ∼45 μm. We examined the effects of the precursor concentration of MAPbI₃ and the mixing of halides (I^– and Br^–) on the charge carrier dynamics, crystal size, and inhomogeneity of the films. The optoelectronic inhomogeneity of MAPbI₃ and MAPb­(I_1–<i>x</i>Br<i>_x</i>)₃ on the sub-millimeter and millimeter scales shows a general correlation with their crystallite sizes, whereas the precursor concentration and halide mixing affect the inhomogeneity in a different way, providing a basis for uniform processing of a multicrystalline perovskite film

Quantifying Hole Transfer Yield from Perovskite to Polymer Layer: Statistical Correlation of Solar Cell Outputs with Kinetic and Energetic Properties

Organic–inorganic hybrid perovskites provide not only an exceptionally rich area of research but also remarkable power conversion efficiency relevant to commercial use. However, developing efficient organic hole transport layers remains challenging, due partly to the subtle electronic behavior of perovskite and complications introduced by the use of reactive dopants. Here we show, through time-resolved microwave conductivity, the quantification of a hole transfer process from methylammonium lead triiodide perovskite to eight kinds of conjugated polymers with and without a Li dopant. The time evolution of hole transfer yield is characterized by kinetic parameters, which are further examined in conjunction with solar cell performance, energetics, and temporal profiles triggered by exposure to air at the minute scale. Using statistics and LASSO (least absolute shrinkage and selection operator) analysis, we identify an accurate descriptor that correlates with device output. This work explores the design of organic hole transport materials, and the presented evaluation technique may be employed as a facile screening method

Computer-Aided Screening of Conjugated Polymers for Organic Solar Cell: Classification by Random Forest

Owing to the diverse chemical structures, organic photovoltaic (OPV) applications with a bulk heterojunction framework have greatly evolved over the last two decades, which has produced numerous organic semiconductors exhibiting improved power conversion efficiencies (PCEs). Despite the recent fast progress in materials informatics and data science, data-driven molecular design of OPV materials remains challenging. We report a screening of conjugated molecules for polymer–fullerene OPV applications by supervised learning methods (artificial neural network (ANN) and random forest (RF)). Approximately 1000 experimental parameters including PCE, molecular weight, and electronic properties are manually collected from the literature and subjected to machine learning with digitized chemical structures. Contrary to the low correlation coefficient in ANN, RF yields an acceptable accuracy, which is twice that of random classification. We demonstrate the application of RF screening for the design, synthesis, and characterization of a conjugated polymer, which facilitates a rapid development of optoelectronic materials

Photon Upconversion through a Cascade Process of Two-Photon Absorption in CsPbBr₃ and Triplet–Triplet Annihilation in Porphyrin/Diphenylanthracene

Photon upconversion constitutes an exceptionally rich area of research in photonics and electronics, where low-energy light is converted to high-energy light through nonlinear processes represented by two-photon absorption (TPA) and triplet–triplet annihilation (TTA). Here, we report a cascade process of TPA in inorganic perovskite quantum dots (PQDs) of CsPbBr₃ and TTA in an organic molecule (9,10-diphenylanthracene) mediated by an octaethylporphyrinatoplatinum­(II) (PtOEP) sensitizer. This sequential energy transfer enables upconversion from four photons from a near-infrared femtosecond laser at 800 nm to one photon at 430 nm with a large anti-Stokes shift of ∼1.3 eV. We characterize the energy transfer from PQDs to PtOEP by picosecond lifetime spectroscopy and a Stern–Volmer plot of the steady-state photoluminescence while considering dynamic and static quenching as well as trivial absorption and Förster (fluorescence) resonance energy transfer. The serial connection of TPA and TTA achieved in a simple system opens up an attractive avenue in nonlinear photonics and harvesting of low-energy photons

Fluorination of Benzothiadiazole–Benzobisthiazole Copolymer Leads to Additive-Free Processing with Meliorated Solar Cell Performance

Processing solvents and conditions have unique importance in the performance of bulk heterojunction organic solar cells. In the present work, we have investigated the role of a primary solvent and solvent additive in the device performance of two benzobisthiazole (BBTz)-based push–pull type polymers. In an inverted cell structure, the BBTz-<i>co</i>-fluorinated benzothiadiazole polymer (PBBTzFT) with a PC₇₁BM acceptor showed additive-free enhanced performance with a power conversion efficiency (PCE) of 6.4% from a 1,2-dichlorobenzene solvent, while the BBTz-<i>co</i>-pyridylthiadiazole polymer (PBBTzPT) showed maximum performance from a chlorobenzene (CB) solution with a 1,8-diiodooctane (DIO) additive (PCE = 2.3%). The detailed investigation by atomic force microscopy and two-dimensional grazing incidence X-ray diffraction corroborates that the fluorination of benzothiadiazole brought about optimal morphology without a solvent additive, the PCE of which is comparable with the previous nonfluorinated analogue (PCE = 6.5%) processed from CB with DIO

Improved Understanding of the Electronic and Energetic Landscapes of Perovskite Solar Cells: High Local Charge Carrier Mobility, Reduced Recombination, and Extremely Shallow Traps

The intriguing photoactive features of organic–inorganic hybrid perovskites have enabled the preparation of a new class of highly efficient solar cells. However, the fundamental properties, upon which the performance of these devices is based, are currently under-explored, making their elucidation a vital issue. Herein, we have investigated the local mobility, recombination, and energetic landscape of charge carriers in a prototype CH₃NH₃PbI₃ perovskite (PVK) using a laser-flash time-resolved microwave conductivity (TRMC) technique. PVK was prepared on mesoporous TiO₂ and Al₂O₃ by one or two-step sequential deposition. PVK on mesoporous TiO₂ exhibited a charge carrier mobility of 20 cm² V^–1 s^–1, which was predominantly attributed to holes. PVK on mesoporous Al₂O₃, on the other hand, exhibited a 50% lower mobility, which was resolved into balanced contributions from both holes and electrons. A general correlation between crystal size and mobility was revealed irrespective of the fabrication process and underlying layer. Modulating the microwave frequency from 9 toward 23 GHz allowed us to determine the intrinsic mobilities of each PVK sample (60–75 cm² V^–1 s^–1), which were mostly independent of the mesoporous scaffold. Kinetic and frequency analysis of the transient complex conductivity strongly support the superiority of the perovskite, based on a significant suppression of charge recombination, an extremely shallow trap depth (10 meV), and a low concentration of these trapped states (less than 10%). The transport mechanism was further investigated by examining the temperature dependence of the TRMC maxima. Our study provides a basis for understanding perovskite solar cell operation, while highlighting the importance of the mesoporous layer and the perovskite fabrication process

Hetero Bis-Addition of Spiro-Acetalized or Cyclohexanone Ring to 58π Fullerene Impacts Solubility and Mobility Balance in Polymer Solar Cells

Fullerene bis-adducts are increasingly being studied to gain a high open circuit voltage (<i>V</i>_oc) in bulk heterojunction organic photovoltaics (OPVs). We designed and synthesized homo and hetero bis-adduct [60]­fullerenes by combining fused cyclohexanone or a five-membered spiro-acetalized unit (SAF₅) with 1,2-dihydromethano (CH₂), indene, or [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). These new eight 56π fullerenes showed a rational rise of the lowest unoccupied molecular orbital (LUMO). We perform a systematic study on the electrochemical property, solubility, morphology, and space-charge-limited current (SCLC) mobility. The best power conversion efficiency (PCE) of 4.43% (average, 4.36%) with the <i>V</i>_oc of 0.80 V was obtained for poly­(3-hexylthiophene) (P3HT) blended with SAF₅/indene hetero bis-adduct, which is a marked advancement in PCE compared to the 0.9% of SAF₅ monoadduct. More importantly, we elucidate an important role of mobility balance between hole and electron that correlates with the device PCEs. Besides, an empirical equation to extrapolate the solubilities of hetero bis-adducts is proposed on the basis of those of counter monoadducts. Our work offers a guide to mitigate barriers for exploring a large number of hetero bis-adduct fullerenes for efficient OPVs

p/n Switching of Ambipolar Bithiazole–Benzothiadiazole-Based Polymers in Photovoltaic Cells

Two new alternating copolymers <b>P1</b> and <b>P2</b>, of bithiazole (BT) and benzothiadiazoles (BTZ), differing in their side chain positioning at the thiophene units which sandwich the BT unit, were designed and synthesized. Both polymers exhibited broad absorption ranging from 300 to 700 nm with a narrow optical bandgap in the film state. Control over structural ordering of polymer chains was achieved in <b>P1</b> by treating with a small amount of additive (1,8-octanedithiol, ODT) as evident by a large red shift of absorption peak and also from the XRD measurements. In contrast, no such effects were observed in the case of <b>P2</b> in the presence of additive. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) experiments revealed that the transient photoconductivity of <b>P1</b> is far superior to that of <b>P2</b>, which is further increased when processed with ODT. The charge carrier mobility, as determined by the space-charge-limited current (SCLC) technique, indicates that <b>P1</b> exhibits both electron and hole mobilities with a clear dominance of the latter. The charge carrier mobilities become higher and more balanced for ODT-modified <b>P1</b> films compared to that of <b>P1</b> alone. TRMC analysis revealed that the photoconductivity of <b>P1</b> reduced when blended with PCBM in the absence of additive, whereas significant enhancement was obtained in presence of additive. The blend with P3HT exhibited an increase in photoconductivity in both the presence and absence of additive. In complete accordance with the TRMC results, in the absence of additive, <b>P1</b> acted as an n-type material (P3HT as donor), whereas in presence of additive, it exhibited ambipolar nature acting as both n-type and p-type (P3HT as donor and PCBM as acceptor, respectively) material. Switching of the major charge carrier species was demonstrated simply by the presence of additive for <b>P1</b> in the present paper