lizhendong

Synthesis of fluorene-based conjugated polyelectrolytes was achieved via Suzuki polycondensation in water and completely open to air. The polyelectrolytes were conveniently purified by dialysis and analysis of the materials showed properties expected for fluorene-based conjugated polyelectrolytes. The materials were then employed in solar cell devices as an interlayer in conjunction with ZnO. The double interlayer led to enhanced power conversion efficiency of 10.75 % and 15.1 % for polymer and perovskite solar cells, respectively.

Fluorene-based conjugated polyelectrolytes were prepared by using a green synthetic route with polymerization in water and in air. High-performance polymer and perovskite solar cells were fabricated using the polyelectrolytes in the cathode interlayer giving power conversion efficiency of 10.75 % and 15.1 %.

Mercury telluride (HgTe) colloidal quantum dots (CQDs) have been developed as promising materials for the short and mid-wave infrared photodetection applications because of their low cost, solution processing, and size tunable absorption in the short wave and mid-infrared spectrum. However, the low mobility and poor photogain have limited the responsivity of HgTe CQD-based photodetectors to only tens of mA W⁻¹. Here, HgTe CQDs are integrated on a TiO₂ encapsulated MoS₂ transistor channel to form hybrid phototransistors with high responsivity of ≈10⁶ A W⁻¹, the highest reported to date for HgTe QDs. By operating the phototransistor in the depletion regime enabled by the gate modulated current of MoS₂, the noise current is significantly suppressed, leading to an experimentally measured specific detectivity D* of ≈10¹² Jones at a wavelength of 2 µm. This work demonstrates for the first time the potential of the hybrid 2D/QD detector technology in reaching out to wavelengths beyond 2 µm with compelling sensitivity.

High-performance hybrid MoS₂/TiO₂/HgTe photodetectors with a responsivity of 10⁶ A W⁻¹, sensitivity of 10¹² Jones, temporal response of <4 ms, and spectral coverage beyond 2 µm, which benefit from the long wavelength light absorption of HgTe quantum dots, huge photogain mechanism, and low noise current, can provide a new platform for mid and long-wave infrared photodetector applications.

Organometallic perovskites, solution-processable materials with outstanding optoelectronic properties and high refractive index, provide a unique platform for alldielectric metamaterials operating at visible frequencies. In article number 1604268, Cesare Soci and co-workers realize perovskite metasurfaces with structural coloring tunable across visible frequencies, which also yields a three-fold increase of luminescence emission in comparison with unstructured perovskite films.

A wide bandgap small molecular acceptor, SFBRCN, containing a 3D spirobifluorene core flaked with a 2,1,3-benzothiadiazole (BT) and end-capped with highly electron-deficient (3-ethylhexyl-4-oxothiazolidine-2-yl)dimalononitrile (RCN) units, has been successfully synthesized as a small molecular acceptor (SMA) for nonfullerene polymer solar cells (PSCs). This SMA exhibits a relatively wide optical bandgap of 2.03 eV, which provides a complementary absorption to commonly used low bandgap donor polymers, such as PTB7-Th. The strong electron-deficient BT and RCN units afford SFBRCN with a low-lying LUMO (lowest unoccupied molecular orbital) level, while the 3D structured spirobifluorene core can effectively suppress the self-aggregation tendency of the SMA, thus yielding a polymer:SMA blend with reasonably small domain size. As the results of such molecular design, SFBRCN enables nonfullerene PSCs with a high efficiency of 10.26%, which is the highest performance reported to date for a large bandgap nonfullerene SMA.

A wide bandgap small molecular acceptor, SFBRCN, containing a 3D spirobifluorene core flanked with two 2,1,3-benzothiadiazole groups and end-capped with two highly electron-deficient (3-ethylhexyl-4-oxothiazolidine-2-yl)dimalononitrile units, has been successfully synthesized as a small molecular acceptor for nonfullerene polymer solar cells with a high efficiency of 10.26%.

Inorganic-organic lead-halide perovskite solar cells have reached efficiencies above 22% within a few years of research. Achieved photovoltages of >1.2 V are outstanding for a material with a bandgap of 1.6 eV – in particular considering that it is solution processed. Such values demand for low non-radiative recombination rates and come along with high luminescence yields when the solar cell is operated as a light emitting diode. This progress report summarizes the developments on material composition and device architecture, which allowed for such high photovoltages. It critically assesses the term “lifetime”, the theories and experiments behind it, and the different recombination mechanisms present. It attempts to condense reported explanations for the extraordinary optoelectronic properties of the material. Amongst those are an outstanding defect tolerance due to antibonding valence states and the capability of bandgap tuning, which might make the dream of low-cost highly efficient solution-processed thin film solar cells come true. Beyond that, the presence of photon recycling will open new opportunities for photonic device design.

Perovskite solar cells show exceptionally high photovoltages. This progress report discusses the current understanding of the main material properties that are responsible for the high electronic quality of the metal-halide perovskites. Amongst them is a pronounced defect tolerance, which facilitates low non-radiative recombination rates and high luminescence yields.

Perovskite solar cells (PSCs) have recently demonstrated high efficiencies of over 22%, but the thermal stability is still a major challenge for commercialization. In this work, the thermal degradation process of the inverted structured PSCs induced by the silver electrode is thoroughly investigated. Elemental depth profiles indicate that iodide and methylammonium ions diffuse through the electron-trasnporting layer and accumulate at the Ag inner surface. The driving force of forming AgI then facilitates the ions extraction. Variations on the morphology and current mapping of the MAPbI₃ thin films upon thermal treatment reveal that the loss of ions occurs at the grain boundaries and leads to the reconstruction of grain domains. Consequently, the deteriorated MAPbI₃ thin film, the poor electron extraction, and the generation of AgI barrier result in the degradation of efficiencies. These direct evidences provide in-depth understanding of the effect of thermal stress on the devices, offering both experimental support and theoretical guidance for the improvement on the thermal stability of the inverted PSCs.

Silver-electrode-induced thermal degradation of the inverted perovskite solar cells is investigated with direct evidences. The diffusion of iodide and methylamine ions is directly observed in the elemental depth profile during thermal treatment only when the Ag electrode is introduced. The loss of ions leads to the reconstruction of the grain boundaries and forming thick PbI₂ gaps between crystal grains.

Low-molecular-weight organic gelators are widely used to influence the solidification of polymers, with applications ranging from packaging items, food containers to organic electronic devices, including organic photovoltaics. Here, this concept is extended to hybrid halide perovskite-based materials. In situ time-resolved grazing incidence wide-angle X-ray scattering measurements performed during spin coating reveal that organic gelators beneficially influence the nucleation and growth of the perovskite precursor phase. This can be exploited for the fabrication of planar n-i-p heterojunction devices with MAPbI₃ (MA = CH₃NH₃⁺) that display a performance that not only is enhanced by ≈25% compared to solar cells where the active layer is produced without the use of a gelator but that also features a higher stability to moisture and a reduced hysteresis. Most importantly, the presented approach is straightforward and simple, and it provides a general method to render the film formation of hybrid perovskites more reliable and robust, analogous to the control that is afforded by these additives in the processing of commodity “plastics.”

Organic gelators, widely used in the processing of commodity “plastics,” are applied to hybrid halide perovskites solidification. They are shown to beneficially influence the nucleation and growth of the perovskite sol–gel precursor phase, leading to a material characterized by a higher stability to moisture and a reduced hysteresis in planar n-i-p heterojunction solar cells.

Organic single-crystalline heterojunctions are composed of different single crystals interfaced together. The intrinsic highly ordered heterostructure in these multicomponent solids holds the capacity for multifunctions, as well as superior charge-transporting properties, promising high-performance electronic applications such as ambipolar transistors and solar cells. However, this kind of heterojunction is not easily available and the preparation methods need to be developed. Recent advances in the efficient strategies that have emerged in yielding high-quality single-crystalline heterojunctions are highlighted here. The advantages and limitations of each strategy are also discussed. The obtained single-crystalline heterojunctions have started to exhibit rich physical properties, including metallic conduction, photovoltaic effects, and so on. Further structural optimization of the heterojunctions to accommodate the electronic device configuration is necessary to significantly advance this research direction.

The recent progress of organic single-crystalline heterojunctions with single crystals interfaced together is highlighted, with a focus on the advances in the efficient strategies for fabricating high-quality heterostructures and exploring the resulting devices from the viewpoint of both their fundamental physics and electronic applications.

A fullerene derivative (α-bis-PCBM) is purified from an as-produced bis-phenyl-C₆₁-butyric acid methyl ester (bis-[60]PCBM) isomer mixture by preparative peak-recycling, high-performance liquid chromatography, and is employed as a templating agent for solution processing of metal halide perovskite films via an antisolvent method. The resulting α-bis-PCBM-containing perovskite solar cells achieve better stability, efficiency, and reproducibility when compared with analogous cells containing PCBM. α-bis-PCBM fills the vacancies and grain boundaries of the perovskite film, enhancing the crystallization of perovskites and addressing the issue of slow electron extraction. In addition, α-bis-PCBM resists the ingression of moisture and passivates voids or pinholes generated in the hole-transporting layer. As a result, a power conversion efficiency (PCE) of 20.8% is obtained, compared with 19.9% by PCBM, and is accompanied by excellent stability under heat and simulated sunlight. The PCE of unsealed devices dropped by less than 10% in ambient air (40% RH) after 44 d at 65 °C, and by 4% after 600 h under continuous full-sun illumination and maximum power point tracking, respectively.

Significantly improved performance of mixed perovskite solar cells, using a facile α-bis-PCBM-containing perovskite growth method during device fabrication, is reported. The newly developed perovskite solar cell exhibits an enhanced power conversion efficiency of 20.8%, along with enhanced stability under heat and illumination.

A ternary nonfullerene polymer solar cell with a high efficiency of 9.70% is realized by using an n-type organic semiconductor ITIC acceptor and two polymer donors of medium bandgap polymer J51 and narrow bandgap polymer PTB7-Th with the polymer weight ratio of 0.8:0.2.

Photodetectors with excellent detecting properties over a broad spectral range have advantages for the application in many optoelectronic devices. Introducing imperfections to the atomic lattices in semiconductors is a significant way for tuning the bandgap and achieving broadband response, but the imperfection may renovate their intrinsic properties far from the desire. Here, by controlling the deviation from the perfection of the atomic lattice, ultrabroadband multilayer MoS₂ photodetectors are originally designed and realized with the detection range over 2000 nm from 445 nm (blue) to 2717 nm (mid-infrared). Associated with the narrow but nonzero bandgap and large photoresponsivity, the optimized deviation from the perfection of MoS₂ samples is theoretically found and experimentally achieved aiming at the ultrabroadband photoresponse. By the photodetection characterization, the responsivity and detectivity of the present photodetectors are investigated in the wavelength range from 445 to 2717 nm with the maximum values of 50.7 mA W⁻¹ and 1.55 × 10⁹ Jones, respectively, which represent the most broadband MoS₂ photodetectors. Based on the easy manipulation, low cost, large scale, and broadband photoresponse, this present detector has significant potential for the applications in optoelectronics and electronics in the future.

Ultrabroadband multilayer MoS₂ photodetectors with the optical response up to 4.7 µm are designed and realized. Their detection properties, ranging from 445 nm (blue) to 2717 nm (mid-infrared), are investigated at room temperature by controlling the S defects, which show the broadest detecting range with low-cost fabrication process and have potential applications in many optoelectronic devices.