To improve the thermal stability of polymer:fullerene bulk heterojunction solar cells, a new polymer, poly2-methoxy-5-(2′-phenylethoxy)-1,4-phenylenevinylene (MPE-PPV), has been designed and ...synthesized, which showed an increased glass transition temperature (T g) of 111 °C. The thermal characteristics and phase behavior of MPE-PPV:6,6-phenyl C61-butyric acid methyl ester (60PCBM) blends were investigated by means of modulated temperature differential scanning calorimetry and rapid heating–cooling calorimetry. The thermal stability of MPE-PPV:60PCBM solar cells was compared with devices based on the reference MDMO-PPV material with a T g of 45 °C. Monitoring of the photocurrent–voltage characteristics at elevated temperatures revealed that the use of high-T g MPE-PPV resulted in a substantial improvement of the thermal stability of the solar cells. Furthermore, a systematic transmission electron microscope study of the active polymer:fullerene layer at elevated temperatures likewise demonstrated a more stable morphology for the MPE-PPV:60PCBM blend. Both observations indicate that the use of high-T g MPE-PPV as donor material leads to a reduced free movement of the fullerene molecules within the active layer of the photovoltaic device. Finally, optimization of the PPV:fullerene solar cells revealed that for both types of devices the use of 6,6-phenyl C71-butyric acid methyl ester (70PCBM) resulted in a substantial increase of current density and power conversion efficiency, up to 3.0% for MDMO-PPV:70PCBM and 2.3% for MPE-PPV:70PCBM.
Bromodomains are epigenetic reader domains, which have come under increasing scrutiny both from academic and pharmaceutical research groups. Effective targeting of the BAZ2B bromodomain by small ...molecule inhibitors has been recently reported, but no structural information is yet available on the interaction with its natural binding partner, acetylated histone H3K14ac. We have assigned the BAZ2B bromodomain and studied its interaction with H3K14ac acetylated peptides by NMR spectroscopy using both chemical shift perturbation (CSP) data and clean chemical exchange (CLEANEX-PM) NMR experiments. The latter was used to characterize water molecules known to play an important role in mediating interactions. Besides the anticipated Kac binding site, we consistently found the bromodomain BC loop as hotspots for the interaction. This information was used to create a data-driven model for the complex using HADDOCK. Our findings provide both structure and dynamics characterization that will be useful in the quest for potent and selective inhibitors to probe the function of the BAZ2B bromodomain.
A new CMOS active mixer topology can operate at low supply voltages by the use of switches exclusively connected to the supply voltages. Such switches require less voltage headroom and avoid ...gate-oxide reliability problems. Mixing is achieved by exploiting two transconductors with cross-coupled outputs, which are alternatingly activated by the switches. For ideal switching, the operation is equivalent to a conventional active mixer. This paper analyzes the performance of the switched transconductor mixer, in comparison with the conventional mixer, demonstrating competitive performance at a lower supply voltage. Moreover, the new mixer has a fundamental noise benefit, as noise produced by the switch-transistors and LO-port is common mode noise, which is rejected at the differential output. An experimental prototype with 12-dB conversion gain was designed and realized in standard 0.18-/spl mu/m CMOS to operate at only a 1-V supply. Experimental results show satisfactory mixer performance up to 4 GHz and confirm the fundamental noise benefit.
A new semiconducting polymer, PDPP3T, with alternating diketopyrrolopyrrole and terthiophene units is presented. PDPP3T has a small band gap of 1.3 eV and exhibits nearly balanced hole and electron ...mobilities of 0.04 and 0.01 cm2 V−1 s−1, respectively, in field-effect transistors (FETs). By the combination of two identical ambipolar transistors, an inverter was constructed that exhibits a gain of ∼30. When PDPP3T was combined with 60PCBM or 70PCBM in a 1:2 weight ratio, photovoltaic cells were made that provide a photoresponse up to 900 nm and an AM1.5 power conversion efficiency of 3.8 or 4.7%, respectively. In contrast to the almost constant FET mobility, the efficiency of the photovoltaic cells was found to be strongly dependent on the molecular weight of PDPP3T and the use of diiodooctane as a processing agent.
A new easily accessible, high molecular weight, alternating dithieno‐diketopyrrolopyrrolophenylene copolymer provides high electron and hole mobilities exceeding 0.02 cm2 V−1 s−1 in FETs and AM1.5 ...power conversion efficiencies of 4.6% and 5.5% in solar cells when combined with 60PCBM and 70PCBM. The performance of the solar cells strongly depends on the use of a processing agent.
A solution‐processed polymer tandem cell fabricated by stacking two single cells in series is demonstrated. The two bulk‐heterojunction subcells have complementary absorption maxima at λmax ∼ 850 nm ...and λmax ∼ 550 nm, respectively. A composite middle electrode is applied that serves both as a charge‐recombination center and as a protecting layer for the first cell during spin‐coating of the second cell. The subcells are electronically coupled in series, which leads to a high open‐circuit voltage of 1.4 V, equal to the sum of each subcell. The layer thickness of the first (bottom) cell is tuned to maximize the optical absorption of the second (top) cell. The performance of the tandem cell is presently limited by the relatively low photocurrent generation in the small‐bandgap polymer of the top cell. The combination of our tandem architecture with more efficient small‐bandgap materials will enable the realization of highly efficient organic solar cells in the near future.
A solution‐processed organic photovoltaic tandem cell (see figure and cover) is demonstrated that is constructed from two polymers (PTBEHT/PCBM, PFDTBT/PCBM) with complementary absorption spectra that absorb from the UV to the near‐IR. The tandem solar cell is electrically connected in series and the open‐circuit voltage of the tandem is the sum of the open‐circuit voltages of the two subcells.
The structures of a dimeric mutant of the Lac repressor DNA-binding domain complexed with the auxiliary operators
O2 and
O3 have been determined using NMR spectroscopy and compared to the structures ...of the previously determined Lac–
O1 and Lac–nonoperator complexes. Structural analysis of the Lac–
O1 and Lac–
O2 complexes shows highly similar structures with very similar numbers of specific and nonspecific contacts, in agreement with similar affinities for these two operators. The left monomer of the Lac repressor in the Lac–
O3 complex retains most of these specific contacts. However, in the right half-site of the
O3 operator, there is a significant loss of protein–DNA contacts, explaining the low affinity of the Lac repressor for the
O3 operator. The binding mode in the right half-site resembles that of the nonspecific complex. In contrast to the Lac–nonoperator DNA complex where no hinge helices are formed, the stability of the hinge helices in the weak Lac–
O3 complex is the same as in the Lac–
O1 and Lac–
O2 complexes, as judged from the results of hydrogen/deuterium experiments.
In organic solar cells, photoexcitation of the donor or acceptor phase can result in different efficiencies for charge generation. We investigate this difference for four different 2-pyridyl ...diketopyrrolopyrrole (DPP) polymer–fullerene solar cells. By comparing the external quantum efficiency spectra of the polymer solar cells fabricated with either 60PCBM or 70PCBM fullerene derivatives as acceptor, the efficiency of charge generation via donor excitation and acceptor excitation can both be quantified. Surprisingly, we find that to make charge transfer efficient, the offset in energy between the HOMO levels of donor and acceptor that govern charge transfer after excitation of the acceptor must be larger by ∼0.3 eV than the offset between the corresponding two LUMO levels when the donor is excited. As a consequence, the driving force required for efficient charge generation is significantly higher for excitation of the acceptor than for excitation of the donor. By comparing charge generation for a total of 16 different DPP polymers, we confirm that the minimal driving force, expressed as the photon energy loss, differs by about 0.3 eV for exciting the donor and exciting the acceptor. Marcus theory may explain the dichotomous role of exciting the donor or the acceptor on charge generation in these solar cells.
A wideband IM3 cancellation technique for CMOS attenuators is presented. With proper transistor width ratios, the dominant distortion currents of transistor switches cancel each other. As a result, a ...high IIP3 robust to PVT variations can be achieved without using large transistors. Two prototypes in a 0.16 μm standard bulk CMOS process are presented: a Π-attenuator with four discrete settings obtains +26 dBm IIP3 and +3 dBm 1 dB-compression point (CP) for 50 MHz to 5 GHz with only 0.0054 mm 2 active area, and a similar T-attenuator system which obtains +27 dBm IIP3 and +13 dBm CP for 50 MHz to 5.6 GHz with only 0.0067 mm 2 active area.
Tin oxide nanoparticles are employed as an electron transporting layer in solution‐processed polymer solar cells. Tin oxide based devices yield excellent performance and can interchangeably be used ...in conventional and inverted device configurations. In combination with poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer, tin oxide forms an effective interconnecting layer (ICL) for tandem solar cells. Conventional and inverted tandem cells with this ICL provide efficiencies up to 10.4% in good agreement with optical‐electrical modeling simulations. The critical advantage of tin oxide in an ICL in a conventional tandem structure over the commonly used zinc oxide is that the latter requires the use of a pH‐neutral formulation of PEDOT:PSS to fabricate the ICL, limiting the open‐circuit voltage (VOC) because of its low work function. The SnO2/PEDOT:PSS ICL, on the other hand, provides a nearly loss‐free VOC.
Solution‐processed layers of PEDOT:PSS and SnO2 nanoparticles serve as an interconnecting layer (ICL) for solution‐processed tandem polymer solar cells in p‐i‐n and n‐i‐p configurations, providing power conversion efficiencies over 10%. The resilience of SnO2 against acidic PEDOT:PSS dispersions enables fabricating p‐i‐n tandem cells with negligible loss in an open‐circuit voltage, giving it a distinct advantage compared to ubiquitously used ZnO.
PDF
