Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction

Use of efficient anode cathode buffer layer (CBL) is crucial to improve the efficiency of organic photovoltaic cells. Here we show that using a double CBL, Ca/Alq3, allows improving significantly cell performances. The insertion of Ca layer facilitates electron harvesting and blocks hole collection, leading to improved charge selectivity and reduced leakage current, whereas Alq3 blocks excitons. After optimisation of this Ca/Alq3 CBL using CuPc as electron donor, it is shown that it is also efficient when SubPc is substituted to CuPc in the cells. In that case we show that the morphology of the SubPc layer, and therefore the efficiency of the cells, strongly depends on the deposition rate of the SubPc film. It is necessary to deposit slowly (0.02 nm/s) the SubPc films because at higher deposition rate (0.06 nm/s) the films are porous, which induces leakage currents and deterioration of the cell performances. The SubPc layers whose formations are kinetically driven at low deposition rates are more uniform, whereas those deposited faster exhibit high densities of pinholes

Laser–induced photo-detachment diagnostic for interrogating pulsed ECR–driven plasmas: Application to H−^− and D−^− negative ions

International audienceThe present work is devoted to an experimental setup tailored to study time-resolved processes relative to negative ion formation in ECR-driven plasmas. It refers to a laser-induced electron photo-detachment system synchronized with H2 and D2 ECR-plasmas being sustained by 2.45 GHz bursts in the kHz range. The system is combined with electrostatic probe time-resolved measurements and information is obtained both on the formation path and the yield enhancement of H − and D − negative ions

H−^{-} and D−^{-} production efficiency in a multi-dipole ECR-plasma source as a function of gas pressure

International audienceThe electron cyclotron resonance (ECR) negative ion source “Prometheus I” is operated either with high purity H2 (> 99.999%) or D2 (> 99.8%) to probe H$^{-}$ and D$^{-}$ ions, respectively, and examine the isotope effect within a wide range of gas pressure. These ions are predominantly formed in the bulk plasma by dissociative attachment (DA) of low-energy (cold) electrons to highly ro-vibrationally excited molecules. The latter result mainly from the radiative decay and excitation (EV) process sustained by high-energy (hot) electrons heated in the ECR zones. Langmuir probe and laser photo-detachment measurements are realized within the pressure range 0.27 to 2.67 Pa under constant microwave power (0.9 kW). It is revealed that: (i) the plasma potential, cold electron temperature, and cold electron density tend to be higher in deuterium; (ii) no pronounced difference in the hot electron density and temperature is found between the two plasmas; and (iii) overall a similar H$^{-}$ and D$^{-}$ negative ion yield (up to 6×10$^{9}$ cm$^{-3}$; under the present conditions) is achieved. However, for equal plasma densities an isotope effect is exhibited showing higher H$^{-}$ density over the entire pressure range. Finally, the n$_{H}$- / n ratio is constantly higher than the n$_{D}$- / n$_{e}$ one and they both peak around 1.33 Pa

Laser-induced photodetachment diagnostic for interrogating pulsed ECR-driven plasmas: Application to H- and D- negative ions

Discharges sustained in the pulsed mode of operation are of great interest on a fundamental level as they may unveil important information on the plasma kinetics. The present work is devoted to an experimental setup tailored to study time-resolved processes relative to negative ion formation in ECR-driven plasmas. It refers to a laser-induced electron photo-detachment system synchronized with H 2 and D 2 ECR-plasmas, sustained by 2.45 GHz bursts in the kHz range. The system is combined with electrostatic probe time-resolved measurements and information is obtained both on the formation path and the yield enhancement of H − and D − negative ions