Adrien Bou

Indium tin oxide-free transparent and conductive electrode based on SnOx | Ag | SnOx for organic solar cells

A SnOx | Ag | SnOx multilayer deposited by E-beam evaporation is proposed as transparent anode for a (poly-3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction based Organic Solar Cell (OSC). Such multilayers are studied and manufactured with the objective to give to the electrode its best conductivity and transparency in the visible spectral range. A transfer matrix method numerical optimization of the thicknesses of each layer of the electrode is developed to limit the number of test samples which would have been manufactured whether an empirical method was chosen. Optical characterization of the deposited SnOx and Ag thin films is performed to determine the dispersion of the complex refractive indices which are used as input parameters in the model. A satisfying agreement between numerical and experimental optical properties is found. The bare tri-layer electrodes show low sheet resistance (as low as 6.7 Ω/□) and the whole Glass | SnOx | Ag | SnOx structure prese...

Optical and electrical properties of structured multilayer with tunable transparency rate

An experimental study has been carried out on structured multilayer with tunable transparency rate. In this paper, we present the optical and electrical characterization of an oxide | metal | oxide structured electrode manufactured by e-beam deposition and patterned by a lift-off process. The obtained samples are made of grids with different geometrical parameters that lead to varying surface coverage rate on glass. The electrical and optical parameters of SnOx|Ag|SnOx grids are investigated to determine the efficiency, sustainability and limitations of such structures. A linear relationship between the transmittance of the electrodes and the increase of the surface coverage rate is obtained. Coupled to an optimization process, we are able to define a high transparency in a chosen spectral range. Electrical results show a relative stability of the resistivity from 2.9 × 10 − 4 Ω.cm for an as-grown electrode to 5.6 × 10 − 4 Ω.cm for a structured electrode with a surface coverage rate of 59%.

Optical role of the thin metal layer in a TiOx/Ag/TiOx transparent and conductive electrode for organic solar cells

One possible alternative to ITO, the most commonly used transparent and conductive electrode (TCE) for Organic Solar Cells (OSCs) and other optoelectronic components, is to use an oxide|metal|oxide multilayer. Glass|cathode|ZnO (20 nm)|P3HT:PCBM (250 nm)|PEDOT:PSS (50 nm)|Ag (150 nm) inverted OSC structures are realized, where the cathode can be a TiOx|Ag|TiOx or ITO reference TCE. The sizing of the TiOx|Ag|TiOx (TAT) TCE structure is numerically realized by optimization of the normalized squared electric field inside the active P3HT:PCBM layer. The optimized TAT design in the whole design is different from the one involving optimization of transparency at the output of the trilayer structure in air. A photovoltaic efficiency of 2.7% is obtained for OSC with the TiOx (22 nm)|Ag (15 nm)|TiOx (19 nm) structure and can be compared to the 3.14% of efficiency obtained with the ITO reference. The short-circuit current density is identified as the crucial photoelectrical parameter. The morphology of the silver layer in TAT can give rise to an exaltation of the electromagnetic field, leading to an enhanced and undesirable absorption inside the metal layer. This exaltation is dependent of the thickness of the metal layer and induces changes in current density proportional to the normalized squared electric field inside this layer. The lost in short-circuit current density is estimated between 0.3 and 0.6 mA cm−2, and is comparable to a thickness variation of 20 nm for both TiOx layers or 2.5 nm of the silver layer. We define an exaltation coefficient of the bare electrode, which can be considered as a factor of merit to qualify the quality of the optical role of the silver layer and thereby of the trilayer electrode.

Numerical and experimental study of SnOx | Ag | SnOx multilayer as indium-free transparent electrode for organic solar cells

We propose a SnOx | Ag | SnOx multilayer, deposited in a continuous vacuum atmosphere by E-beam evaporation, as transparent anode for a (poly-3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction based Organic Solar Cell (OSC). Optical characterization of the deposited SnOx is performed to determine the dispersion of the complex refractive index. A Transfer Matrix Method (TMM) numerical optimization of the thicknesses of each layer of the electrode is realized to limit the number of manufactured samples. A numerical study using the morphology of the silver inserted between the oxide layers as input data is performed with a Finite Difference Time Domain (FDTD) method to improve the accordance between measurement and optical model. Multilayers are manufactured with the objective to give to the electrode its best conductivity and transparency in the visible spectral range by using the results of the optical optimization. These bare tri-layer electrodes show low sheet resistance (<10 Ω/□) and mean transparency on [400-700] nm spectral band as high as 67 % for the whole Glass | SnOx | Ag | SnOx structure. The trilayer is then numerically studied inside a P3HT:PCBM bulk heterojunction based OSC structure. Intrinsic absorption inside the sole active layer is calculated giving the possibility to perform optical optimization on the intrinsic absorption efficiency inside the active area by considering the media embedding the electrodes.

Enhanced light trapping using plasmonic nanoparticles

Plasmonics is a new light trapping method used in photovoltaic (PV) solar cells. A significant enhancement of the scattered and absorbed incident light due to the use of silver nanoparticles (Ag-NPs) was observed, which yield to the exaltation of the electromagnetic field in the vicinity of these NPs. In this context, we investigate optically and morphologically the effect of the NPs size dependence on the localized surface plasmon resonance. Extinction, absorption and scattering cross sections are calculated using Mie theory.