Search

Ternary bulk heterojunctions using a wide band gap polymer P3HT and a narrow band gap polymer PTB7 as donors and ICBA as acceptor have been fabricated using a novel dual-feed approach in an ultrasonic spray. The binary blend of two donor polymers in a BHJ formed by a conventional method in which the two donor polymers are mixed intimately in a common solvent may lead to unfavourable phase morphology due to unfavourable interaction between them and puts constraints on the composition of the polymer blend in the BHJ. The unfavourable interaction may cause severe molecular disorder leading to charge recombination trap site, and thereby decreases the device performance. In the new method proposed in this paper intimate mixing of two donor polymers is avoided, which removes the constraint on the fraction of second donor in the first. Moreover, it also results in better polymer ordering leading to significantly higher hole mobility compared to that achieved with conventional method. The steady state photoluminescence study depicts more efficient FRET in P3HT:PTB7 binary blend prepared with dual channel method as compared to that prepared with single channel mode. With this method, ternary BHJ can be prepared even with higher concentration of the third component to have maximum power absorption, without compromising its optoelectronic properties. Although the superior properties of BHJ formed with the new dual-feed method did not reflected in similar performance in device functioning, with better choice of the donors and acceptor and with more control on nanoscale morphology through selection of proper solvents the device performance may improve to acceptable level. This report opens a new way of BHJ preparation in ternary organic solar cell fabrication.

A comprehensive study regarding the effect of different solvent vapours on organolead halide perovskite properties is lacking. In the present work, the impact of exposing CH3NH3PbI3 films to the vapours of commonly available solvents has been studied. The interaction with perovskite has been correlated to solvent properties like dielectric constant, molecular dipole moment, Gutmann donor number and boiling point. Changes in the crystallinity, phase, optical absorption, morphologies at both nanometer and micrometer scale, functional groups and structures were studied using X-ray diffraction, UV-visible absorption, FE-SEM, FTIR and Raman spectroscopies. Among the aprotic solvents DMSO and DMF vapours deteriorate the crystallinity, phase, and optical, morphological and structural properties of the perovskite films in a very short time, but due to the difference in solvent property values acetone affects the perovskite properties differently. Polar protic 2-propanol and water vapours moderately affect the perovskite properties. However 2-propanol can solvate the organic cation CH3NH3+ more efficiently as compared to water and a considerable difference was found in the film properties especially the morphology at the nanoscale. Nonpolar chlorobenzene vapour minutely affects the perovskite morphology but toluene was found to enhance perovskite crystallinity. Solvent properties can be effectively used to interpret the coordination ability of a solvent. The present study can be immensely useful in understanding the effects of different solvent vapours and also their use for post-deposition processing (like solvent vapour annealing) to improve their properties.

Organometallic halide perovskite based solar cells are considered as the foundation of future photovoltaic technology. In these types of solar cells, it has been emphasized that the bulk heterojunction active layer architecture may show superior performance than the bilayer active layer architecture due to the increase in the interfacial area by intermixing both donor and acceptor phases in the bulk heterojunction. Organometallic halide perovskite with suitable acceptor in bulk heterojunction architecture can be a promising active layer in perovskite solar cells. Conventionally, the perovskite and acceptor are mixed together in a single solvent before thin film formation. Though this offers a one-step synthesis way, limited solubility of perovskite and acceptor in single solvent puts major constraint on the formation of bulk heterojunction through one-step solution processable method. This paper describes a new way of one-step synthesis of bulk heterojunction using surfactant free microemulsion in slot die method, which removes the constraint of limited solubility of the two phases in a single solvent. Emulsion of DMSO (solvent for CH3NH3PbI3) and cyclohexane (solvent for PCBM) stabilized with acetone was used for making perovskite:fullerene bulk heterojunction. Solvent evaporation dynamics has been simulated to get deeper understanding of emulsion solidification leading to bulk heterojunction formation. Structural and optical studies support the formation of bulk heterojunction for efficient charge separation at donor:acceptor interfaces. A perovskite solar cell employing this bulk heterojunction has also been reported.

Synthesis of monomorphic, SnS nanoparticles without using a capping agent is a difficult task with chemical route of synthesis. This paper reports on synthesis of tin monosulfide (SnS) nanopartilces with dimension in the quantum-dot regime using surfactant free microemulsion with single microemulsion scheme. This has been achieved by reaction in microreactors in the CME (C: chlorobenzene, M: methanol and E: ethylene glycol) microemulsion system. This is an easy and controllable chemical route for synthesis of SnS nanoparticles. Nanoparticle diameter showed prominent dependence on microemulsion concentration and marginal dependence on microemulsion temperature in the temperature range studied. The SnS nanoparticles formed with this method form stable dispersion in Tolune.

We here present a way of preparing the polymer: fullerene BHJ using dual feed method which can lead to formation of pure phases. In this report, we present results of our initial experiments in this direction. The effect of process parameters on the thickness and surface roughness of the active layer has been discussed. The structural and optical properties have been studied using the optical microscope, UV—visible spectroscopy and photoluminescence spectroscopy. Significant PL quenching indicates efficient charge separation in the BHJ formed using this technique. We have also compared the BHJ thin films prepared with this dual feed ultrasonic technique with the single feed spray method. The BHJ formed using this technique has been used as an active layer in OSC.