The Rational Control of Precursor Concentration in Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have attracted tremendous attention due to their ideal optoelectronic properties, such as high color purity, high fluorescence quantum yield, and tunable light color. The perovskite layer plays a decisive role in the performance of PeLEDs and the solvent engineering of the perovskite layer is the key technological breakthrough in preparing high quality films. In this study, we have proposed the strategy of adding different amounts of solvents to the perovskite precursor solution to optimize the morphology of perovskite films and device performance. As a result, with the decreasing concentration of perovskite precursor solution, the perovskite film morphology is smoother and more favorable for carrier injection and combing, which induces an enhanced external quantum efficiency. The maximum luminance of PeLEDs was increased from 1667 cd/m2 to 9857 cd/m2 and the maximum current efficiency was increased from 6.7 cd/A to 19 cd/A. This work provides a trend to achieve improved film morphology and device performance for perovskite optoelectronic devices.

Recent Advances of Film–Forming Kinetics in Organic Solar Cells

Solution–processed organic solar cells (OSC) have been explored widely due to their low cost and convenience, and impressive power conversion efficiencies (PCEs) which have surpassed 18%. In particular, the optimization of film morphology, including the phase separation structure and crystallinity degree of donor and acceptor domains, is crucially important to the improvement in PCE. Considering that the film morphology optimization of many blends can be achieved by regulating the film–forming process, it is necessary to take note of the employment of solvents and additives used during film processing, as well as the film–forming conditions. Herein, we summarize the recent investigations about thin films and expect to give some guidance for its prospective progress. The different film morphologies are discussed in detail to reveal the relationship between the morphology and device performance. Then, the principle of morphology regulating is concluded with. Finally, a future controlling of the film morphology and development is briefly outlined, which may provide some guidance for further optimizing the device performance.

Templated Growth of Fullerene C60 Crystals by Triptycene in Polymer Blend Films

<p>Molecular semiconductors such as fullerene C60 have become ubiquitous components of organic electronic devices, owing to their electronic structure and favourable material processing properties. In most conjugated polymer-fullerene films that form the active layer in bulk heterojunction (BHJ) organic solar cells, organisation of the fullerene phases to the correct nanoscale dimensions for exciton charge separation and transportation to the device electrodes is driven by excess fullerene addition. While this approach can deliver acceptable film morphology for a BHJ solar cell, it is not optimal as the photoactive polymer component of the film becomes diluted by C60 thereby reducing device efficiency. This motivates a supramolecular approach as an alternative method to control fullerene assembly and give morphological control of conjugated polymer films. Triptycene (TPC) is a readily available molecule whose rigid paddle wheel structure and hydrophobicity present three excellent C60 binding cavities. Triptycene has the potential to template the macroscopic assembly of fullerene molecules within a polymer-fullerene blend film, thereby controlling phase separation without excess fullerene addition. In this project, the ability of TPC to template the assembly of C60 was investigated in single crystals, polymer films, and in functional electronic devices. Blue-shifted fluorescence from TPC·C60 co-crystals was used as a spectroscopic signature to probe the molecular environment of C60 dispersed through an optically transparent polystyrene polymer film, and confirm that TPC hosts C60 molecules within the polymer matrix. Ultraviolet-visible (UV-Vis) spectroscopy of the polystyrene:C60:TPC films confirmed a reduction in the orbital overlap between adjacent C60 molecules providing further evidence that TPC had spatially separated C60 molecules upon templating the macroscopic assembly. When TPC was added to conjugated polymer poly[2-methoxy-5-(2-ethyhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and MEHPPV: C60 films as a blend additive, fluorescence spectroscopy identified two unique effects: (1) the suppression of excimer states when TPC spatially separated the conjugated polymer chains, and (2) the assembly of C60 into larger domains to drive polymer and C60 phase separation, giving morphological control of the polymer film. The fabrication of polystyrene:C60:TPC sandwich devices showed the electronic conduction of C60 was unaltered by spatial separation and reduction in electronic coupling between neighbouring C60 molecules caused by TPC templation. MEHPPV: C60 BHJ solar cells suffered a loss in photocurent when TPC was added to the active layer when compared to fabricated devices that used excess fullerene addition to control film morphology. However, due to time constraints, only one polymer film composition was able to be tested. Since the polymer film morphology was shown to be sensitive to the molar ratios of C60 and TPC, there is immense potential to further investigate TPC as a blend additive in conjugated polymer films and optimise the film composition to obtain desirable morphology for a BHJ solar cell. The functionalisation of TPC could provide a method to further enhance interactions between TPC and C60 and provide greater control over C60 self-assembly within a polymer film.</p>

Templated Growth of Fullerene C60 Crystals by Triptycene in Polymer Blend Films

<p>Molecular semiconductors such as fullerene C60 have become ubiquitous components of organic electronic devices, owing to their electronic structure and favourable material processing properties. In most conjugated polymer-fullerene films that form the active layer in bulk heterojunction (BHJ) organic solar cells, organisation of the fullerene phases to the correct nanoscale dimensions for exciton charge separation and transportation to the device electrodes is driven by excess fullerene addition. While this approach can deliver acceptable film morphology for a BHJ solar cell, it is not optimal as the photoactive polymer component of the film becomes diluted by C60 thereby reducing device efficiency. This motivates a supramolecular approach as an alternative method to control fullerene assembly and give morphological control of conjugated polymer films. Triptycene (TPC) is a readily available molecule whose rigid paddle wheel structure and hydrophobicity present three excellent C60 binding cavities. Triptycene has the potential to template the macroscopic assembly of fullerene molecules within a polymer-fullerene blend film, thereby controlling phase separation without excess fullerene addition. In this project, the ability of TPC to template the assembly of C60 was investigated in single crystals, polymer films, and in functional electronic devices. Blue-shifted fluorescence from TPC·C60 co-crystals was used as a spectroscopic signature to probe the molecular environment of C60 dispersed through an optically transparent polystyrene polymer film, and confirm that TPC hosts C60 molecules within the polymer matrix. Ultraviolet-visible (UV-Vis) spectroscopy of the polystyrene:C60:TPC films confirmed a reduction in the orbital overlap between adjacent C60 molecules providing further evidence that TPC had spatially separated C60 molecules upon templating the macroscopic assembly. When TPC was added to conjugated polymer poly[2-methoxy-5-(2-ethyhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and MEHPPV: C60 films as a blend additive, fluorescence spectroscopy identified two unique effects: (1) the suppression of excimer states when TPC spatially separated the conjugated polymer chains, and (2) the assembly of C60 into larger domains to drive polymer and C60 phase separation, giving morphological control of the polymer film. The fabrication of polystyrene:C60:TPC sandwich devices showed the electronic conduction of C60 was unaltered by spatial separation and reduction in electronic coupling between neighbouring C60 molecules caused by TPC templation. MEHPPV: C60 BHJ solar cells suffered a loss in photocurent when TPC was added to the active layer when compared to fabricated devices that used excess fullerene addition to control film morphology. However, due to time constraints, only one polymer film composition was able to be tested. Since the polymer film morphology was shown to be sensitive to the molar ratios of C60 and TPC, there is immense potential to further investigate TPC as a blend additive in conjugated polymer films and optimise the film composition to obtain desirable morphology for a BHJ solar cell. The functionalisation of TPC could provide a method to further enhance interactions between TPC and C60 and provide greater control over C60 self-assembly within a polymer film.</p>

Processing and Preparation Method for High-Quality Opto-Electronic Perovskite Film

The key to improving the energy conversion efficiency of perovskite solar cells lies in the optimization of the film morphology. The optical and electrical properties of the perovskite film, such as light absorption, carrier diffusion length, and charge transport, are all directly affected by the film morphology. Therefore, this review starts from the perovskite solar cells structure, and it summarizes the state-of-art perovskite film fabrication technologies and the caused film morphology to the performance perovskite solar cells. The spin coating method has an enormous waste of materials and only a small area of the device can be utilized. It is difficult to be used in commercial manufacturing. However, due to the high efficiency of this preparation method, it is irreplaceable in the initial research and development of perovskite materials, and so this method will be popular for a long time in the laboratory. Chemical vapor deposition and thermal vapor deposition have high technical requirements and a good repeatability of processing and manufacturing, and large-scale production can be realized. It may be the first technology to admit industrial application; the scratch coating method and slot-die have significant technical aspects. The similarity of the roll-to-roll manufacturing technology is also an efficient preparation method. Still, to achieve high-efficiency devices, it is necessary to consider the thickness control of each functional layer, and to find or prepare perovskite paste. Finally, we summarized the various fabrication processes and the prospects for the commercialization of perovskite solar cells. We predict that to achieve the commercialization of perovskite solar cells, the existing fabrication technologies should be optimized and more studies should be conducted.