over 30% detailed balance limiting efficiency, as well as to its earth-abundant and environment-benign constituents. [1-3] The increase in power conversion efficiency to a record of 12.6% in the last decade has demonstrated the huge potential of these materials. [4,5] However, as one of the most complicated compound semiconductors, kesterite has much more intricate defect chemistry than its counterparts, Cu(In,Ga)Se 2 (CIGS) and CdTe, [6-8] making the control of intrinsic defects a major challenge. Deep intrinsic defects like Sn Zn antisites and related [Cu Zn +Sn Zn ] clusters act as deep recombination centers, leading to the short carrier lifetime. [7,9,10] Additionally, the large population of defect clusters like [2Cu Zn +Sn Zn ] introduces considerable potential (i.e., band or electrostatic) fluctuation. [11] Consequently, the performance of CZTSSe solar cells are currently stagnated by the large open-circuit voltage (V OC) deficit. [12,13] To address the detrimental intrinsic defects and defect clusters in CZTSSe absorber, multiple strategies have been employed. As suggested by the first-principle calculations, the formation energy of intrinsic defects and Kesterite-based Cu 2 ZnSn(S,Se) 4 semiconductors are emerging as promising materials for low-cost, environment-benign, and high-efficiency thin-film photo voltaics. However, the current state-of-the-art Cu 2 ZnSn(S,Se) 4 devices suffer from cation-disordering defects and defect clusters, which generally result in severe potential fluctuation, low minority carrier lifetime, and ultimately unsatisfactory performance. Herein, critical growth conditions are reported for obtaining high-quality Cu 2 ZnSnSe 4 absorber layers with the formation of detrimental intrinsic defects largely suppressed. By controlling the oxidation states of cations and modifying the local chemical composition, the local chemical environment is essentially modified during the synthesis of kesterite phase, thereby effectively suppressing detrimental intrinsic defects and activating desirable shallow acceptor Cu vacancies. Consequently, a confirmed 12.5% efficiency is demonstrated with a high V OC of 491 mV, which is the new record efficiency of pure-selenide Cu 2 ZnSnSe 4 cells with lowest V OC deficit in the kesterite family by E g /q-Voc. These encouraging results demonstrate an essential route to overcome the long-standing challenge of defect control in kesterite semiconductors, which may also be generally applicable to other multinary compound semiconductors.

A series of hydrophobically associating poly(N-isopropylacryamide) (PNIPAM) containing low amounts (0.06−0.88 mol %) of fluorocarbon (CF3(CF2)7 - ) was prepared by copolymerization of NIPAM and 2-(N-ethylperfluorooctanesulfonamido)ethyl methacrylate. Hydrophobic association of the copolymers in an aqueous medium was investigated by fluorospectroscopy in which both pyrene (Py) and fluorocarbon-substituted pyrene (PyCORf) were used as probes. In comparison with unmodified pyrene, using PyCORf with the same fluorocarbon substituent as in the PNIPAM copolymers proved to be more informative for monitoring hydrophobic associations of the copolymers due to its affinity for the microdomains of the fluorocarbon chains. Both the monomer emission intensity, I 375, and the monomer to excimer ratio of intensities, I 375/I 550, of PyCORf were good indicators of the dependence of the association on the fluorocarbon content of the copolymers and their concentration.

Dielectric capacitors have the highest charge/discharge speed among all electrical energy devices, but lag behind in energy density. Here we report dielectric ultracapacitors based on ferroelectric films of Ba(Zr0.2,Ti0.8)O3 which display high-energy densities (up to 166 J cm–3) and efficiencies (up to 96%). Different from a typical ferroelectric whose electric polarization is easily saturated, these Ba(Zr0.2,Ti0.8)O3 films display a much delayed saturation of the electric polarization, which increases continuously from nearly zero at remnant in a multipolar state, to a large value under the maximum electric field, leading to drastically improved recyclable energy densities. This is achieved by the creation of an adaptive nano-domain structure in these perovskite films via phase engineering and strain tuning. The lead-free Ba(Zr0.2,Ti0.8)O3 films also show excellent dielectric and energy storage performance over a broad frequency and temperature range. These findings may enable broader applications of dielectric capacitors in energy storage, conditioning, and conversion.

Fluorocarbon-containing hydrophobically associating polymers have been synthesized by copolymerization of acrylic acid with a small amount of C8 fluorocarbon-containing methacrylate. The association behavior of the fluorocarbon-modified poly(acrylic acid) (FA) over a broad pH range has been investigated by a fluorescent probe technique and viscosity measurements. The copolymer has the strongest intermolecular association and maximum viscosity at the acidic condition of pH 5.5. Both pyrene and fluorocarbon-substituted pyrene (PyCORf) are usable to detect this strong association and its dependences on both the fluorocarbon content and polymer concentration. Less acidic pH causes progressive disruptions of hydrophobic association, leading to a dramatic decrease in viscosity. At pH > 7, the stretched polymer chains reach a viscosity plateau much lower than the maximum viscosity but still higher than the viscosity of the poly(acrylic acid) homopolymer. This indicates that relatively weak associations are present. PyCORf, due to its high affinity to the fluorocarbon domains, is effective in monitoring the formation of this kind of weak association while pyrene fails to do so.