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In this work, macro- and nanodiagnostic procedures for working, third-generation photovoltaic devices based on a modified polymer:fullerene (P3HT:PCBM) absorber were conducted using atomic force microscopy (AFM) and impedance spectroscopy (IS) equipment. All experiments were performed both in the dark and under irradiation with a specific light wavelength. Photoactive Kelvin probe force microscopy (p-KPFM) and impedance spectroscopy (p-IS) experiments were conducted on half- and whole-solar cell devices. Based on the p-KPFM measurements, the surface potential (SP) and surface photovoltage (SPV) on top of the active layer at the micro/nanoscale were estimated for various light wavelengths (red, green, blue, and white). For light in the red spectrum range, which was associated with an optical absorption edge and acceptor states that occurred in the band gap of the P3HT material after doping the donor polymer with iodine, the SPV was measured at levels of 183 mV, 199 mV, and 187 mV for the samples with 0%, 5% and 10% iodine doping, respectively. In addition, a macroscale investigation enabling the determination of the electrical parameters of the studied organic solar cells (OSCs) was carried out using p-IS. Based on the data obtained during p-IS experiments, it was possible to propose a series electrical equivalent circuit to define and describe the charge transfer phenomenon in the OSCs. Estimations of data obtained from the fitting of the experimental results of p-IS under white light allowed us to evaluate the average diffusion time of electric charges at 8.15 µs, 16.66 µs, and 24.15 µs as a function of organic layer thickness for the device without doping and with 5% and 10% iodine doping. In this study, we demonstrated that correlating information obtained at the macro- and nanoscale enabled a better understanding of the electrical charge distribution of OSCs for indoor applications. [ABSTRACT FROM AUTHOR]

The paper presents synthesis and characterization of nine new thiazolyl-(phenyldiazenyl)-2H-chromen-2-one dyes. The impact of substituent structure in thiazole ring in the synthesized azocoumarin derivatives on electrochemical properties, photoisomerization process and photovoltaic response was examined. The dyes were electrochemically active and undergo reduction and oxidation processes. They showed low electrochemically estimated energy band gap in the range of 1.71–2.13 eV. Photoisomerization process of the synthesized molecules was studied in various solvents such as ethanol, chloroform and N,N-dimethylformamide (DMF) upon the UV illumination. It was found that novel azodyes showed reversible trans-cis-trans isomerization and exhibited long thermal back to the trans form, that was even 7 days in DMF. Selected azocoumarin were molecularly dispersed in polystyrene for preparation of guest-host azopolymer systems to study the cis-trans thermal isomerization of obtained dyes in solid state. The photovoltaic activity of the azochromophores was tested in bulk-heterojunction solar cells. They acting as weak donors in device with structure ITO/PEDOT:PSS/dye:PC70BM/Al. No photovoltaic response of cells with azocoumarin derivatives bearing 4-fluorobenzene, 3,4-dichlorobenzene, or 4-(1-adamantyl) unit was found. Additionally, dye which showed the best activity was examined in three-component solar cells ITO/PEDOT:PSS/PTB7:PC70BM:dye/PFN/Al. [ABSTRACT FROM AUTHOR]

Optical and structural properties of a blend thin film of (1:1 wt.) of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) doped with iodine (I2) and then exposed to a stepwise heating were reported and compared with the properties of doped P3HT films. The UV-Vis(T) absorption measurements were performed in situ during annealing runs, at the precisely defined temperatures, in a range of 20–210 °C. It was demonstrated that this new method allows one to observe the changes of absorption spectra, connected with the iodine release and other structural processes upon annealing. In addition, the thermally-induced changes of the exciton bandwidth (W) and the absorption edge parameters, i.e., the energy gap (EG) and the Urbach energy (EU) were discussed in the context of different length of conjugation and the structural disorder in polymers and blends films. During annealing, several stages were distinguished and related to the following processes as: the iodine escape and an increase in P3HT crystallinity, the orderly stacking of polymer chains, the thermally inducted structural defects and the phase separation caused by an aggregation of PCBM in the polymer matrix. Moreover, the detailed X-ray diffraction studies, performed for P3HT and P3HT:PCBM films, before and after doping and then after their thermal treatment, allowed us to consider the structural changes of polymer and blend films. The effect of iodine content and the annealing process on the bulk heterojunction (BHJ) solar cells parameters was checked, by the impedance spectroscopy (IS) measurements and the J-V characteristics registration. All of the investigated P3HT:PCBM blend films showed the photovoltaic effect; the increase in power conversion efficiency (PCE) upon iodine doping was demonstrated. [ABSTRACT FROM AUTHOR]