An integrated DC/DC converter with online monitoring of hot-carrier degradation

An integrated DC/DC converter with online monitoring of the degradation induced by hot-carrier stress (HCD) in new generation power LDMOS transistors is proposed. In particular, when a relatively high drain voltage is applied during on-state regime (switching phase), degradation mechanisms lead to an increase of the transistor on-resistance (RON). To this purpose, the converter is able to dynamically estimate the RON of the power LDMOS and to provide its value to the user during normal operation. The presented solution, developed in STMicroelectronics 90nm BCD technology, features a non-invasive current sensing and voltage sampling architecture, which is applied to a common DC/DC boost converter to evaluate the resistance of the power LDMOS. Without lack of generality, this specific sensing structure can be applied to any kind of converter, e.g. buck or buck-boost, as it does not require any change in the main conversion circuit

PV Cell Characteristic Extraction to Verify Power Transfer Efficiency in Indoor Harvesting System

A method is proposed to verify the efficiency of low-power harvesting systems based on Photovoltaic (PV) cells for indoor applications and a Fractional Open-Circuit Voltage (FOCV) technique to track the Maximum Power Point (MPP). It relies on an algorithm to reconstruct the PV cell Power versus Voltage (P-V) characteristic measuring the open circuit voltage and the voltage/current operating point but not the short-circuit current as required by state-of-the-art algorithms. This way the characteristic is reconstructed starting from the two values corresponding to standard operation modes of dc-dc converters implementing the FOCV Maximum Power Point Tracking (MPPT) technique. The method is applied to a prototype system: an external board is connected between the transducer and the dc-dc converter to measure the open circuit voltage and the voltage/current operating values. Experimental comparisons between the reconstructed and the measured P-V characteristics validate the reconstruction algorithm. Experimental results show the method is able to clearly identify the error between the transducer operating point and the one corresponding to the maximum power transfer, whilst also suggesting corrective action on the programmable factor of the FOCV technique. The proposed technique therefore provides a possible way of estimating MPPT efficiency without sampling the full P-V characteristic

Air-Stable Benzimidazoline n-Type Dopants for Conductive Host Materials with Low Electron Affinities

Nowadays a growing interest is devoted to molecular reductants for solution-processable organic semiconductors such as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), thermoelectric generators (TEGs), organic field-effect transistors (OFETs), and circuitry in which they can increase the conductivity, reduce bulk ohmic losses and/or decrease carrier-injection barriers.[1] They can also modulate the work function (WF) of inorganic electrode materials and push the performance of inverted perovskite solar cell by boosting the conductivity of PCBM type ETMs. However, the availability of high-performance and airstable solution-processable n-doped materials remains limited, primarily due to the low electron affinity of n-type materials that strongly restricts the n-doping level. Benzimidazoline-based reductants (Figure1) have recently emerged as efficient and air-stable n-type dopants in electron transporting materials (ETMs) to increase electrical conductivities.[2] Hence we designed and synthesized a series of Benzimidazoline based compounds as air-stable n-dopants and their doping abilities have been surveyed by analysing the electron conductivity trend of organic semiconductors. Moreover an in-depth study of their electrochemical characteristics have been carried out and their molecular orbital energy levels investigated. The most efficient n-doping molecules are intended to largescale, printed electronics for energy-harvesting and storage applications

Efficient sunlight harvesting by A4 b-pyrrolic substituted ZnII porphyrins : a mini-review

Dye-Sensitized Solar Cells (DSSCs) are a highly promising alternative to conventional photovoltaic silicon-based devices, due to the potential low cost and the interesting conversion efficiencies. A key-role is played by the dye, and porphyrin sensitizers have drawn great interest because of their excellent light harvesting properties mimicking photosynthesis. Indeed, porphyrins are characterized by strong electronic absorption bands in the visible region up to the near infrared and by long-lived \u3c0* singlet excited states. Moreover, the presence of four meso and eight \u3b2-pyrrolic positions allows a fine tuning of their photoelectrochemical properties through structural modification. Trans-A2BC push-pull ZnII porphyrins, characterized by a strong and directional electron excitation process along the push-pull system, have been extensively investigated. On the other hand, A4 \u3b2-pyrrolic substituted tetraaryl ZnII porphyrins, which incorporate a tetraaryl porphyrinic core as a starting material, have received lower attention, even if they are synthetically more attractive and show several advantages such as a more sterically hindered architecture and enhanced solubility in most common organic solvents. The present contribution intends to review the most prominent A4 \u3b2-substituted ZnII porphyrins reported in the literature so far for application in DSSCs, focusing on the strategies employed to enhance the light harvesting capability of the dye and on a comparison with meso-substituted analogs

Insight into the Properties of Heteroleptic Metal Dithiolenes: Multistimuli Responsive Luminescence, Chromism, and Nonlinear Optics

A comprehensive investigation of the functional properties of heteroleptic donor-M-acceptor dithiolene complexes Bu4N[MII(L1)(L2)] is presented (M = Pd, Pt). The acceptor L1 consists of the chiral (R)-(+)α-methylbenzyldithiooxamidate ((R)-α-MBAdto), the donor L2 is 2-thioxo-1,3-dithiole-4,5-dithiolato (dmit) in 1 (Pd) and 2 (Pt), 1,2-dicarbomethoxyethylenedithiolate (ddmet) in 3 (Pd) and 4 (Pt), or [4′,5′:5,6][1,4]dithiino[2,3-b]quinoxaline-1′,3′-dithiolato (quinoxdt) in 5 (Pd) and 6 (Pt). L1 is capable of undergoing proton exchange and promoting crystal formation in noncentrosymmetric space groups. L2 has different molecular structures while it maintains similar electron-donating capabilities. Thanks to the synergy of the ligands, 1-6 behave as H+ and Ag+ switchable linear chromophores. Moreover, the compounds exhibit a H+-switchable second-order NLO response in solution, which is maintained in the bulk for 1, 3, and 4 when they are embedded into a PMMA poled matrix. 5 and 6 show unique anti-Kasha H+ and Ag+ tunable colored emission originating from the quinoxdt ligand. A correlation between the electronic structure and properties is shown through density functional theory (DFT) and time-dependent DFT calculations

4D-π-1A Type β-Substituted ZnII-Porphyrins : Ideal Green Sensitizers for Building-Integrated Photovoltaics [4D-pi-1A type beta-substituted Zn-II-porphyrins: ideal green sensitizers for building-integrated photovoltaics]

Two novel green \u3b2-substituted ZnII-porphyrins, G1 and G2, based on a 4D-\u3c0-1A type substitution pattern have been synthesized. Their enhanced push-pull character, by reduction of H-L energy gaps, promotes broadening and red-shifting of absorption bands. The effective synthetic pathway and the remarkable spectroscopic properties make G2 ideal for BIPV application

Electronic properties of electron-deficient Zn(II) porphyrins for HBr splitting

Two different high potential Zn(II) porphyrin designs carrying either 4 or 5 meso pentafluorophenyl moieties as electron acceptor groups and a further electron withdrawing branch inserted in either the \u3b2 (1) or meso (2) position were tested in photoelectrosynthetic cells for HBr splitting. Photoaction spectra in the presence of HBr showed that red photons up to 700 nm could be harvested and converted and that 2 performed better than 1, thanks to better electronic properties of the excited state, favored by the insertion of the benzothiadiazole electron withdrawing group. Photoanodic performances in the presence of HBr, however, remained low, due to inefficient regeneration of the oxidized sensitizer as a result of an insufficient driving force for Br- oxidation

Influence of alkoxy chains envelope on the interfacial photoinduced processes in tetraarylporphyrin-sensitized solar cells

The introduction of alkoxy chains in the molecular architecture of meso push-pull porphyrins is of paramount importance aiming at high performing dye-sensitized solar cells (DSSCs) based on these specific sensitizers. Recently, we have demonstrated that the same approach is fruitful even if it is applied to tetraarylporphyrins with an acceptor/anchoring substituent in the \u3b2-pyrrolic position. In particular, among the ortho-ortho, the ortho-para and the ortho-functionalization of the aryl rings with an octyloxy chain, we identified the latter as the most performing in the series, showing a good balance between the dye loading and the reduction of \u3c0-\u3c0 aggregation. Herein, focusing our attention on the mono-ortho-functionalized molecular structure, we have investigated the effect of the alkoxy chain length and nature on the reduction of dye-to-dye aggregation as well as on the enhancement of light harvesting capabilities, finding an almost linear relationship between the device photon conversion efficiency (PCE) and the alkoxy chain length both in the presence and in the absence of a co-disaggregating agent

The reaction of molibdenum(VI) dioxo derivatives with hetrocumulenes

The reactions of ArNSO (Ar = p-MeC6H4) with cis-Mo(O)2(chel)2 (chel = S2CNEt2, CH3COCH- COCHH3) give the molybdenum(VI) oxo-arylimido derivatives, Mo(O)(NAr)(hel)2, and sulphur dioxide. From cis-Mo(O)2(S2CNEt2)2 and CyNCO (Cy = C6H11) the dimeric Mo2O3(S2CNEt2)4 is obtained, with the concomitant formation of carbon dioxide and biuret, (CyNHCO)2NCy. The spectroscopic properties of the molybdenum(VI) oxo-arylimido derivatives are reported and the possible reaction mechanisms are discussed

Tailoring Transition Metal Complexes for Nonlinear Optics Applications. 2. A Theoretical Investigation of the Second-Order Nonlinear Optical Properties of M(CO)5L Complexes (M = Cr, W; L = Py, PyCHO, Pyz, PyzBF3, BPE, BPEBF3)

The authors report an ab initio study of 2nd-order nonlinear optical (NLO) properties and absorption electronic spectra of push-pull transition metal chromophores [M(CO)5L] (M = Cr, W; L = pyridine (Py), 4-formyl-pyridine (PyCHO), pyrazine (Pyz), trans-1,2-bis(4-pyridyl)ethylene (BPE)). Pyz and BPE are considered either with 1 N atom free or interacting with the strong acceptor BF3. All of the mol. properties were calcd. using 2 different and methodol. independent approaches: the time dependent and coupled perturbed d. functional theories (TDDFT and CPDFT) and the sum-over-states (SOS) approach, where the excited states are obtained via the single CI (SCI) ab initio method. DFT results are in acceptable agreement with the exptl. energy values of electronic transitions (with the exception of chromophores with the large greek p-delocalization, like BPE); SCI calcns. overestimate excitation energies and produce an inversion in the order of dM greek pi*L and dM greek p*CO transitions. The SCI-SOS approach gives 1st-order hyperpolarizabilities, basically in agreement as trend and values with the expts. and seems to be a tool generally suitable for the evaluation of these properties also for transition metal complexes. However, the 1st-order hyperpolarizabilities computed using the CPDFT approach are consistently overestimated in comparison with the exptl. results, esp. in the case of a ligand with large greek p-delocalization. Also the 2-level approxn. taking into account only the lowest energy charge transfer excitation (e.g., dM greek p*L) is not applicable to chromophores with the extended greek p-delocalized ligand (BPE) coordinated to a transition metal, due to significant contributions originating from intraligand greek pL greek p*L transitions. This study reports a detailed anal. and comparison of electronic NLO effects of transition metal complexes computed with DFT and ab initio SCI-SOS methodol