Francis Lin

Pinhole-Free and Surface-Nanostructured NiOx Film by Room-Temperature Solution Process for High-Performance Flexible Perovskite Solar Cells with Good Stability and Reproducibility

Recently, researchers have focused on the design of highly efficient flexible perovskite solar cells (PVSCs), which enables the implementation of portable and roll-to-roll fabrication in large scale. While NiOx is a promising material for hole transport layer (HTL) candidate for fabricating efficient PVSCs on a rigid substrate, the reported NiOx HTLs are formed using different multistep treatments (such as 300-500 °C annealing, O2-plasma, UVO, etc.), which hinders the development of flexible PVSCs based on NiOx. Meanwhile, the features of nanostructured morphology and flawless film quality are very important for the film to function as highly effective HTL of PVSCs. However, it is difficult to have the two features coexist natively, particularly in a solution process that flawless film will usually come with smooth morphology. Here, we demonstrate the flawless and surface-nanostructured NiOx film from a simple and controllable room-temperature solution process for achieving high performance flexible PVSCs with good stability and reproducibility. The power conversion efficiency (PCE) can reaches a promising value of 14.53% with no obvious hysteresis (and a high PCE of 17.60% for PVSC on ITO glass). Furthermore, the NiOx-based PVSCs show markedly improved air stability. Regarding the performance improvement, the flawless and surface-nanostructured NiOx film can make the interfacial recombination and monomolecular Shockley-Read-Hall recombination of PVSC reduce. In addition, the formation of an intimate junction of large interfacial area at NiOx film/the perovskite layer improve the hole extraction and thus PVSC performances. This work contributes to the evolution of flexible PVSCs with simple fabrication process and high device performances.

Toward All Room-Temperature, Solution- Processed, High-Performance Planar Perovskite Solar Cells: A New Scheme of Pyridine-Promoted Perovskite Formation

A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs). The PVSCs show high efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrates, respectively, which are the best efficiencies reported to date for PVSCs fabricated by room-temperature solution-processed techniques. The flexible PVSCs show a remarkable power-per-weight of 23.26 W g-1 .

Dithienopicenocarbazole Based Acceptors for Efficient Organic Solar Cells with Optoelectronic Response Over 1000 nm and an Extremely Low Energy Loss.

Two cheliform non-fullerene acceptors, DTPC-IC and DTPC-DFIC, based on a highly electron-rich core, dithienopicenocarbazole (DTPC), are synthesized, showing ultra-narrow bandgaps (as low as 1.21 eV). The two-dimensional nitrogen-containing conjugated DTPC possesses strong electron-donating capability, which induces intense intramolecular charge transfer and intermolecular π-π stacking in derived acceptors. The solar cell based on DTPC-DFIC and a spectrally complementary polymer donor, PTB7-Th, showed a high power conversion efficiency of 10.21% and an extremely low energy loss of 0.45 eV, which is the lowest among reported efficient OSCs.

High‐Efficiency Nonfullerene Organic Solar Cells with a Parallel Tandem Configuration

In this work, a highly efficient parallel connected tandem solar cell utilizing a nonfullerene acceptor is demonstrated. Guided by optical simulation, each of the active layer thicknesses of subcells are tuned to maximize its light trapping without spending intense effort to match photocurrent. Interestingly, a strong optical microcavity with dual oscillation centers is formed in a back subcell, which further enhances light absorption. The parallel tandem device shows an improved photon-to-electron response over the range between 450 and 800 nm, and a high short-circuit current density (J SC ) of 17.92 mA cm-2 . In addition, the subcells show high fill factors due to reduced recombination loss under diluted light intensity. These merits enable an overall power conversion efficiency (PCE) of >10% for this tandem cell, which represents a ≈15% enhancement compared to the optimal single-junction device. Further application of the designed parallel tandem configuration to more efficient single-junction cells enable a PCE of >11%, which is the highest efficiency among all parallel connected organic solar cells (OSCs). This work stresses the importance of employing a parallel tandem configuration for achieving efficient light harvesting in nonfullerene-based OSCs. It provides a useful strategy for exploring the ultimate performance of organic solar cells.

Room temperature formation of organic–inorganic lead halide perovskites: design of nanostructured and highly reactive intermediates

Recently, organic–inorganic lead halide perovskites have been intensively studied for use in solar cells because of their low cost and high performance. Most of the efficient perovskite solar cells (PVSCs) need layer-dependent high-temperature treatment for each layer of the multilayered structures, increasing the fabrication complexity. In addition, high temperature processes hinder their applications in flexible devices. Therefore, it is highly desirable to develop room-temperature processed methods for controllably forming perovskite films which can simplify the complicated device process and promote emerging flexible device technologies. In this work, we propose a room-temperature scheme of ligand-promoted formation of high quality perovskite films through the judicious design of nanostructured PbI2·(L)x intermediates, where L denotes the ligand. The high quality perovskite films are free of pinholes and impurities, and have high crystallinity. Using our room-temperature crystallization of perovskite films, we have fabricated highly efficient room-temperature solution-processed PVSCs with a power conversion efficiency (PCE) of 17.21% (the current best PVSCs based on perovskite fabricated at room temperature have a PCE of <16%). Meanwhile, we have experimentally investigated the effects of different ligands on building the nanostructured PbI2·(L)x intermediates, and thus the purity, morphology, and optoelectronic performances of the resultant perovskite films. Through thermodynamic and kinetic studies, we theoretically study the reactivity of nanostructured PbI2·(L)x intermediates, thus elucidating the possible mechanism of ligand-promoted perovskite formation. Furthermore, with the experimental and theoretical studies, we establish the selection rules for identifying ideal ligands for the formation of high-quality perovskite films. This work offers a fundamental understanding of ligand effects on the formation of perovskite films for the future design of high-performance and low-cost perovskite-based optoelectronic devices.

Long-lived, Non-Geminate, Radiative Recombination of Photogenerated Charges in a Polymer:Small-Molecule Acceptor Photovoltaic Blend

Minimization of open-circuit-voltage ( VOC) loss is required to transcend the efficiency limitations on the performance of organic photovoltaics (OPV). We study charge recombination in an OPV blend comprising a polymer donor with a small molecule nonfullerene acceptor that exhibits both high photovoltaic internal quantum efficiency and relatively high external electroluminescence quantum efficiency. Notably, this donor/acceptor blend, consisting of the donor polymer commonly referred to as PCE10 with a pseudoplanar small molecule acceptor (referred to as FIDTT-2PDI) exhibits relatively bright delayed photoluminescence on the microsecond time scale beyond that observed in the neat material. We study the photoluminescence decay kinetics of the blend in detail and conclude that this long-lived photoluminescence arises from radiative nongeminate recombination of charge carriers, which we propose occurs via a donor/acceptor CT state located close in energy to the singlet state of the polymer donor. Additionally, crystallographic and spectroscopic studies point toward low subgap disorder, which could be beneficial for low radiative and nonradiative losses. These results provide an important demonstration of photoluminescence due to nongeminate charge recombination in an efficient OPV blend, a key step in identifying new OPV materials and materials-screening criteria if OPV is to approach the theoretical limits to efficiency.

New push–pull polyene chromophores containing a Michler's base donor and a tricyanofuran acceptor: multicomponent condensation, allopolar isomerism and large optical nonlinearity

The high chemo-selectivity of bis-aldehydes for condensation with both basic and acidic active methylene compounds facilitates a one-pot, three-component reaction to produce dipolar polyene chromophores as the major products for electro-optics.