The effect of net carriers at the interconnection layer in tandem organic solar cells

Tandem cell with structure of indium tin oxide (ITO)/ molybdenum oxide (MoO3)/ fullerene (C60) / copper phthalocyanine (CuPc)/ C60 / tris-8-hydroxy- quinolinato aluminum (Alq3)/Al was fabricated to study the effect of net carriers at the interconnection layer. The open circuit voltage and short circuit current were found to be 1.15 V and 0.56 mA/cm2, respectively. Almost the same performance (1.05 V, 0.58 mA/cm2) of tandem cell with additional recombination layer (ITO/MoO3/C60/Alq3/Al/Ag/MoO3/CuPc/C60/Alq3/Al) demonstrates that carrier balance is more crucial than carrier recombination. The net holes at the interconnection layer caused by more carrier generation from the back cell on one hand would enhance the recombination with electrons from the front cell and on the other hand would quench the excitons produced in CuPc of the back cell.

Improved Photocatalytic Water Splitting Activity of Highly Porous WO3 Photoanodes by Electrochemical H+ Intercalation

WO3 photoanodes are widely used in photoelectrochemical catalysis, but typically the as-synthesized material is annealed before application. It is therefore desirable to explore less energy-intensive treatments. In this study, WO3 films of up to 3.9 μm thickness were obtained by galvanostatic anodization of tungsten foil in a neutral-pH Na2SO4 and NaF electrolyte, also containing a NaH2PO2 additive (to suppress O2 accumulation on the pore walls). Additionally, the WO3 photoanodes were modified by applying a cathodic reduction (H+ intercalation) and anodic activation treatment in-situ. XPS spectra revealed that intercalation modifies WO3 films; the amount of W5+-O and O-vacancy bonds was increased. Furthermore, subsequent activation leads to a decrease of the W5+ signal, but the amount of O-vacancy bonds remains elevated. The as-prepared and reduced (intercalated & activated) films were tested as OER photoanodes in acidic 0.1 M Na2SO4 media, under illumination with a 365 nm wavelength LED. It was observed that thinner films generated larger photocurrents. The peculiarities detected by XPS for reduced films correlate well with their improved photocatalytic activity. Photo-electrochemical impedance and intensity modulated photocurrent spectroscopies were combined with steady-state measurements in order to elucidate the effects of H+ intercalation on photoelectrochemical performance. The reduction results in films with enhanced photoexcited charge carrier generation/separation, improved conductivity, and possibly even suppressed bulk recombination. Thus, the intercalation & activation adopted in this study can be reliably used to improve the overall activity of as-synthesized WO3 photoanodes, and particularly of those that are initially poorly photoactive.

Effect of contact barrier height on performances of BaSi2 heterojunction and homojunction solar cells

The effects of contact barrier height on performances of Si/BaSi2 p–n heterojunction, BaSi2 p–n homojunction and Si/BaSi2/Si p–i–n heterojunction were numerical calculated. Band energy diagram, built-in electric field, carrier generation and carrier transportation distributed in the devices are comprehensively investigated. BaSi2 p–n homojunction solar cells are very sensitive to front contact barrier height due to the high light absorption coefficient of front p-BaSi2 layer. Si/BaSi2 p–n heterojunction and BaSi2 p–n homojunction solar cells with donor concentration [Formula: see text] less than [Formula: see text] are apparently affected by back contact barrier height. The ideal [Formula: see text]-Si/BaSi2/[Formula: see text]-Si p–n solar cell achieves a high [Formula: see text] of 1.131 V, suggesting a promising and alternative structure to gain excellent BaSi2-based solar cells once the Urbach tail states and defects can be effectively eliminated. The results help to fundamentally understand operation mechanism and provide intuitive guidance for achieving high-efficiency BaSi2 solar cells.

Parameterization of charge transport process with avalanche multiplication in irradiated Si p-i-n structures at T = 1.9 K

The study is devoted to the treatment of in situ radiation tests results for silicon p-i-n detectors of relativistic protons, which showed the two-stage process of charge transport with avalanche multiplication at a temperature of 1.9 K. The goal of the work is to extract the carrier transport parameters from the experimental data obtained by transient current technique. For that, the impact of a spatial nonuniformity of carrier generation by the laser and spreading of the drifting carrier cloud due to diffusion on the current pulse response formation were considered. The mathematical procedure proposed for the current pulse simulation showed a key contribution of avalanche multiplication in the signal formation and allowed direct estimation of the multiplication factor from the experimental pulses. It is found that this factor only slightly depends on the bias voltage, which suggests the electric field inside the detector to be affected by the space-charge-limited current.

Effect of Laser Parameters on Optical Stealth Transmission System Performance

The performance of an optical stealth transmission system based on gain-switched laser depends largely on the laser parameters. Modulation frequency, bias current, and modulation current are considered to study the covertness and bit error rate performance of the optical stealth transmission system. According to optical stealth carrier generation with time spreading and all-optical encoding, the stealth signals are derived. A complementary encoding scheme is adopted in the system simulation. The simulation results show that the temporal and spectral characteristics of the generated stealth signal can be changed by adjusting the bias current, modulation current, and modulation frequency. However, there is a trade-off between bit error rate performance and covertness of the stealth channel. Under the premise of error-free transmission, the bias current and modulation frequency should be reduced and the modulation current should be improved to optimize the covertness of the stealth channel.

Hot Carrier Photocurrent through MOS Structure

Flow of photocurrent through the metal-oxide-semiconductor structure induced by the pulsed infrared CO2 laser is investigated experimentally. In the case of a perfect insulator, the photocurrent has a photocapacitive character. Its rise is based on the hot carrier phenomenon; no carrier generation is present, only redistribution of laser-heated carriers takes place at the semiconductor surface. The magnitude of this displacement current is related to the capacitance of the structure and is dependent on the rate of the laser pulse change as well as on the laser light intensity. This effect can find application in the detection of fast infrared laser pulses as well as in the development of infrared photovaractors. Operation of such devices would not require cryogenic temperatures what is usually needed by the long-wavelength infrared semiconductor technique.