Igor Tazbir

Silver Nanoparticles in PEDOT:PSS Layer for Polymer Solar Cell Application

We compare the performance of polymer solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) with silver nanoparticles (Ag NPs) incorporated in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The structure of constructed solar devices was ITO/PEDOT:PSS:Ag NPs/P3HT:PCBM/Al. Typical polyol chemistry was used to synthesize silver in water solution. Ag nanoparticles were investigated by UV-vis, atomic force microscopy (AFM), and dynamic light scattering (DLS) methods. We investigated influence of amount of silver in a hole transporting layer on the performance of bulk heterojunction polymer solar cells. The value of power conversion efficiency (PCE), equal to 2.16% under simulated 100 mW/cm2 AM 1.5G irradiation, was found for device created in air with 60 µL of Ag NPs added to 1 mL of PEDOT:PSS. Along with the increase amount of Ag NPs from 60 to 150 µL, the PCE decrease was found. Stability of solar cells with Ag was also investigated. The loss in value of PCE after 8 months was found in the range 13–47% depending on the device architecture. The solar cells were additionally measured with impedance spectroscopy.

Photosensitive self-assembling materials as functional dopants for organic photovoltaic cells

New photosensitive liquid crystalline compounds with a specific molecular structure have been designed in order to use them as functional dopants for organic photovoltaic devices. The main idea is to establish the effect of doping on the bulk-heterojunction solar cell properties and characteristics. As a part of basic characterisation, the self-assembling behaviour of three new organic compounds has been determined. The resulting photovoltaic devices with a P3HT:PCBM active layer doped by the designed photosensitive materials were investigated by UV-Vis spectroscopy, electrochemical measurements, cyclic voltammetry experiments, AFM surface morphology studies and impedance spectroscopy. The obtained results are summarised and discussed in terms of power conversion efficiency improvement considering the specific chemical structure of the compounds used as functional dopants and the annealing temperature of an active layer. The molecular structure of compounds used as a dopant has a strong effect on the value of short circuit current density. However, no significant effect of the dopant in the P3HT:PCBM active layer on the open circuit voltage and fill factor has been found.

Polymer solar cells with a TiO2:Ag layer

Photovoltaic (PV) polymer solar cells with Ag and titanium dioxide were fabricated to improve the PV performance by increasing the amount of Ag in TiO2 (by 3, 5, 7, and 10%). Sol–gel method was used to obtain amorphous or crystalline form of titanium dioxide layers. The solar cells with poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester active layer in two various positions of titanium dioxide in device were tested. Higher PV performance was received by introducing TiO2 with 5% of Ag between ITO and PEDOT:PSS in device and by heating the layer at 130 °C. The viscosity of applied PEDOT:PSS strongly influences the values of power conversion efficiency of the constructed polymer devices with titanium dioxide.

Analysis of the surface decoration of TiO2 grains using silver nanoparticles obtained by ultrasonochemical synthesis towards organic photovoltaics

In this article, we present a wet ultrasonochemical synthesis of nanocrystalline TiO2 powders in the anatase form in ethanol solution and their surface decoration using uniformly dispersed Ag metallic nanoparticles of about 4 nm at concentration of n = 0.5 to 2.5 wt% and those of 10–20 nm larger at a higher concentration than 1 wt%. The structure of the prepared composites was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman and X-ray photoelectron spectroscopy (XPS). Optical properties were determined using UV-vis spectroscopy. Six polymer solar cells with modification by an TiO2/n-Ag hole transporting layer were manufactured and studied under AM 1.5G-simulated solar illumination (100 mW cm−2). The best performance was obtained for a device with the ITO/(PEDOT:PSS):1.5%Ag in TiO2/P3HT:PCBM/Al architectures. Under these conditions, a PCE of 2.07% with open circuit voltage Voc = 0.612 V, short circuit current density Jsc = 5.94 mA cm−2, and fill factor FF = 0.57 was achieved. Additionally, devices were tested by electrochemical impedance spectroscopy under illumination and a well-fitted equivalent circuit was proposed. Finally, our idea of the linkage of TiO2/n-Ag with PEDOT:PSS and P3HT in the constructed devices taking into account the amount of Ag in TiO2 was proposed.

Towards designing polymers for photovoltaic applications: A DFT and experimental study of polyazomethines with various chemical structures

Theoretical studies of polyazomethines (PAZs) with various chemical structures designated for photovoltaic applications are presented. PAZ energy levels and optical properties were calculated within density-functional theory (DFT and TDDFT) framework for 28 oligomers (monomer, dimer and trimer) of PAZs. The correlations between chemical structure of PAZ and location of its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels were examined. It turned out that the presence of triaminophenylene, dimethoxydiphenylene and fluorine group raises the orbital energies. As a consequence, it is a factor which improves the photovoltaic efficiency of solar cell built on the base of the corresponding PAZ and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). On the contrary, quinone, 1,3,5-triazine and perfluorophenylene groups lower orbital energies and have negative influence on the photovoltaic efficiency. Moreover, calculations for methyl, ethyl and butyl analogs of P3HT as well as polythiophenes were performed and compared with the results obtained for PAZs. In addition experimental data are presented, which cover optical, electrochemical and electrical transport properties of the studied PAZs, allowing to determine HOMO and LUMO energies of the polymers and their conductivity. Finally, comparison between calculated and experimental results were made and discussed.