N. A. Radychev

Properties of CdSe films produced via spray pyrolysis of [Cd((NH2)2CSe)2Cl2]

Data are presented on microwave photoconductivity kinetics in CdSe films prepared via spray pyrolysis of aqueous solutions of thiourea complexes on quartz and glass-ceramic substrates at temperatures from 300 to 600°C. The films were characterized by x-ray diffraction and optical absorption and reflection spectroscopies. Microwave photoconductivity (excitation with 8-ns laser pulses at 337 nm) was measured at 295 K by a resonator method in the 9-and 36-GHz ranges. The results indicate that the photoresponse decay kinetics depend on deposition temperature and incident intensity. In the films deposited below 400°C, the photoresponse decay follows a first-order rate law. At deposition temperatures above 450°C, the photoresponse decay cannot be represented by a first-or second-order rate law at low excitation intensities and approaches second-order kinetics at high intensities (> 1015 photons/cm2 per pulse). Analysis of the photoresponse decay kinetics in terms of the interaction between free and trapped electrons, holes, and ions allowed us to formulate a model for the processes involved and to evaluate the rate constant of electron-hole recombination in CdSe: (4–6) × 10−11 cm3/s.

Kinetics of electron-ion processes in CdTe-based solid solutions in the CdTe-CdI2 system

Single-crystal and polycrystalline CdTe-CdI2 solid solutions containing 0.016 to 0.350 mol % CdI2 have been studied using microwave photoconductivity measurements. The results demonstrate that the magnitude of their photoresponse and the shape of the photoresponse decay curve depend on the doping level and the degree of dispersion. The observed effect of doping level on the photogenerated electron decay kinetics in cadmium telluride is interpreted in terms of self-compensation, which leads to redistribution of trap energies. The recombination rate constant for free electrons and holes in CdTe is determined to be (3 ± 1) × 10−11 cm3/s, independent of the doping level and the degree of dispersion of the samples.

Novel Low-Band-Gap Conjugated Polymers Based on Benzotrithiophene Derivatives for Bulk Heterojunction Solar Cells

Two novel conjugated donor–acceptor copolymers P1 and P2 based on acylbenzotrithiophene derivatives were prepared under Stille reaction conditions. Molecular weights of the polymers were determined by gel permeation chromatography. Thermal properties were studied by TGA and DSC methods, while optical and electrochemical properties were studied by UV spectroscopy and cyclic voltammetry. Effect of different fullerene derivatives PC60BM and PC70BM on photovoltaic characteristics was also studied.

New Donor-Acceptor Benzotrithiophene-Containing Conjugated Polymers for Solar Cells

In the present study four new low band gap alternating donor-acceptor copolymers based on benzotrithiophene were synthesized under Stille reaction conditions. All polymers show good solubility in common organic solvents and a broad absorption in the visible region of the solar spectrum. The band gap of polymer films and HOMO levels of polymers were obtained from the voltammograms and vary in the range 1.4–2.4 eV and −5.0 – 5.4 eV, respectively. Open circuit voltage and efficiency of the developed polymer solar cells are in the range 0.33–0.57 V and 0.01–0.14 %, respectively.

Opto-Electrical Properties of Composite Materials Based on Two Benzotrithiophene Copolymers and Fullerene Derivatives

Two donor–acceptor copolymers based on a benzotrithiophene acceptor unit and an electron-donor segment of 4,8-didodecyloxybenzo[1,2-b;4,5-b ]dithiophene were investigated in the view of photovoltaic application. We provided the complete synthesis procedure supported with NMR spectra of the monomers obtained. The resulting copolymers, labeled P1 and P2 in this work, exhibit strong absorption in the visible region with a similar band gap of about 2.2 eV. In spite of the chemical similarity of both copolymers, the photovoltaic and carrier transport properties of the P1- and P2-based devices demonstrated a noticeable difference. Applying an optimization procedure, a power conversion efficiency of 4.6% has been achieved for the P2/PC71BM solar cells.

New narrow-band-gap thiazoloquinoxaline-containing polymers and their use in solar cells with bulk heterojunction

Two new regioregular polymers P1 and P2 with structure of type D–A1–D–A2 have been prepared. The polymers exhibit strong light absorption in the range 300–1100 nm and have band gaps of 1.09 and 1.11 eV, respectively. The HOMO and LUMO energies for P1 and P2 are–5.08/–3.81 and–5.16/–3.85 eV, respectively. Polymer solar cells (PSC) based on P1: PC71BM (1: 2, v/v) and P2: PC71BM (1: 1, v/v) have open-circuit voltage Voc, short circuit current Jsc, and efficiency of 0.79 and 0.84 V, 8.32 and 9.54 mA/cm2, 3.5 and 4.7%, respectively. The PSC based on P2 exhibits higher characteristics due to the presence of fluorine atoms in the structure: their strong electron-withdrawing properties decrease the HOMO level of polymer P2 as compared with that of P1, which increases the Voc value. Moreover, the formation of additional S∙∙∙F contacts leads to the growth of ordering and crystallinity of polymer P2 as compared with P1, which favors an increase in the values of Jsc and filling factor.