ABSTRACT
The addition of small seeding particles into a supersaturated solution is one among the most effective approaches to obtain high-quality semiconductor materials via increased crystallization rates. However, limited study is conducted on this approach for the fabrication of perovskite solar cells. Here, a new strategy-"heterogenous seeding-induced crystallization (hetero-SiC)" to assist the growth of FAPbI3 -based perovskite is proposed. In this work, di-tert-butyl(methyl)phosphonium tetrafluoroborate is directly introduced into the precursor, which forms a low-solubility complex with PbI2 . The low-solubility complex can serve as the seed to induce crystallization of the perovskite during the solvent-evaporation process. Various in situ measurement tools are used to visualize the hetero-SiC process, which is shown to be an effective way of manipulating the nucleation and crystal growth of perovskites. The hetero-SiC process greatly improves the film quality, reduces film defects, and suppresses nonradiative recombination. A hetero-SIC proof-of-concept device exhibits outstanding performance with 24.0% power conversion efficiency (PCE), well over the control device with 22.2% PCE. Additionally, hetero-SiC perovskite solar cell (PSC) stability under light illumination is enhanced and the PSC retains 84% of its initial performance after 1400 h of light illumination.
ABSTRACT
The benchmark tin oxide (SnO2) electron transporting layers (ETLs) have enabled remarkable progress in planar perovskite solar cell (PSCs). However, the energy loss is still a challenge due to the lack of "hidden interface" control. We report a novel ligand-tailored ultrafine SnO2 quantum dots (QDs) via a facile rapid room temperature synthesis. Importantly, the ligand-tailored SnO2 QDs ETL with multi-functional terminal groups in situ refines the buried interfaces with both the perovskite and transparent electrode via enhanced interface binding and perovskite passivation. These novel ETLs induce synergistic effects of physical and chemical interfacial modulation and preferred perovskite crystallization-directing, delivering reduced interface defects, suppressed non-radiative recombination and elongated charge carrier lifetime. Power conversion efficiency (PCE) of 23.02% (0.04 cm2) and 21.6% (0.98 cm2, VOC loss: 0.336 V) have been achieved for the blade-coated PSCs (1.54 eV Eg) with our new ETLs, representing a record for SnO2 based blade-coated PSCs. Moreover, a substantially enhanced PCE (VOC) from 20.4% (1.15 V) to 22.8% (1.24 V, 90 mV higher VOC, 0.04 cm2 device) in the blade-coated 1.61 eV PSCs system, via replacing the benchmark commercial colloidal SnO2 with our new ETLs.
ABSTRACT
Epitaxial growth gives the highest-quality crystalline semiconductor thin films for optoelectronic devices. Here, a universal solution-processed bottom-up quasi-epitaxial growth of highly oriented α-formamidinium lead triiodide (α-FAPbI3 ) perovskite film via a two-step method is reported, in which the crystal orientation of α-FAPbI3 film is precisely controlled through the synergetic effect of methylammonium chloride and the large-organic cation butylammonium bromide. In situ GIWAXS visualizes the BA-related intermediate phase formation at the bottom of film, which serves as a guiding template for the bottom-up quasi-epitaxial growth in the subsequent annealing process. The template-guided epitaxially grown BAFAMA perovskite film exhibits increased crystallinity, preferred crystallographic orientation, and reduced defects. Moreover, the BAFAMA perovskite solar cells demonstrate decent stability, maintaining 95% of their initial power conversion efficiency after 2600 h ambient storage, and 4-time operation condition lifetime enhancement.
ABSTRACT
Several breakthroughs in organic optoelectronic devices with new applications and performance improvement have been made recently by exploiting novel properties of charge transfer complexes (CTCs). In this work, a CTC film formed by coevaporating molybdenum(VI) oxide and pentacene (MoO3:pentacene) shows a strong dipole of 2.4 eV with direction controllability via pre-biasing with an external voltage. While CTCs are most widely known for their much red-shifted energy gaps, there is so far no report on their controllable dipoles. By controlling this dipole with an electrical pre-bias in a MoO3:pentacene CTC based device, current changes over 2 orders of magnitude can be achieved. Kelvin probe force microscopy further confirms that surface potential of the MoO3:pentacene film can be modulated by an external electric field. It is shown for the first time that a dipole of controllable direction can be set up inside a CTC layer by pre-biasing. This concept is further tested by incorporating the CTC layer in organic photovoltaic (OPV) devices. It was demonstrated that by pre-biasing the OPV devices in different directions, their open circuit voltages (Voc) can be significantly tuned via the built-in potentials.
ABSTRACT
Polymer dots (Pdots) have emerged as a new type of fluorescent probe material for biomedical applications and have attracted great interest due to their excellent optical properties and biocompatability. In this work, we report on a red-emitting P3HT Pdot fluorescent probe for intracellular bioimaging. The as-prepared Pdot fluorescent probe exhibits good stability and has a large Stokes shift (121 nm) compared to molecules in tetrahydrofuran (THF). Furthermore, the probe shows low cytotoxicity, broad absorption spectrum, resistance against photodegradation, and good water dispersibility. These advantageous characteristics make P3HT Pdots a promising fluorescent probe material for bioimaging.
Subject(s)
Fluorescent Dyes/chemistry , Fluorescent Dyes/pharmacology , Optical Imaging/methods , Quantum Dots/chemistry , A549 Cells , HumansABSTRACT
High performance organic photovoltaic devices typically rely on type-II P/N junctions for assisting exciton dissociation. Heremans and co-workers recently reported a high efficiency device with a third organic layer which is spatially separated from the active P/N junction; but still contributes to the carrier generation by passing its energy to the P/N junction via a long-range exciton energy transfer mechanism. In this study the authors show that there is an additional mechanism contributing to the high efficiency. Some bipolar materials (e.g., subnaphthalocyanine chloride (SubNc) and subphthalocyanine chloride (SubPc)) are observed to generate free carriers much more effectively than typical organic semiconductors upon photoexcitation. Single-layer devices with SubNc or SubPc sandwiched between two electrodes can give power conversion efficiencies 30 times higher than those of reported single-layer devices. In addition, internal quantum efficiencies (IQEs) of bilayer devices with opposite stacking sequences (i.e., SubNc/SubPc vs SubPc/SubNc) are found to be the sum of IQEs of single layer devices. These results confirm that SubNc and SubPc can directly generate free carriers upon photoexcitation without assistance from a P/N junction. These allow them to be stacked onto each other with reversible sequence or simply stacking onto another P/N junction and contribute to the photocarrier generation.
ABSTRACT
We show the effects of chlorine incorporation in the crystallization process of perovskite film based on a lead acetate precursor. We demonstrate a fabrication process for fast grain growth with highly preferred {110} orientation upon only 5 min of annealing at 100 °C. By studying the correlation between precursor composition and morphology, the growth dynamic of perovskite film in the current system is discussed. In particular, we found that both lead acetate precursor and Cl incorporation are beneficial to perovskite growth. While lead acetate allows fast crystallization process, Cl improves perovskite crystallinity. Planar perovskite solar cells with optimized parameters deliver a best power conversion efficiency of 15.0% and average efficiency of 14.0% with remarkable reproducibility and good stability.
