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/PC 71 BM solar cells.

In this communication, we report the design a low bandgap D-A copolymer consist of fluorinated thiadiazoloquinoxaline (TDQ) as strong acceptor and benzothiophene (BT), denoted as P(ffFITDQ(x)-BT) exhibit broad absorption profile covering from 350 nm to 1000 nm with optical bandgap of 1.26 eV. P(ffFITDQ(x)-BT) showed highest occupied molecular orbital (HOMO) energy level of -5.46 eV which is deeper than that for nonfluorinated counterpart copolymer. The photovoltaic properties were evaluated using conventional devices with a structure of ITO/PEDOT:PSS/P(ffFITDQ(x)-BT):PC71BM/Al. After the optimizations of the P(ffFITDQ(x)-BT) to PC71BM weight ratios, and concentration of the solvent additive (DIO), the devices showed overall power conversion efficiency of 7.27%. The higher value of PCE of this device is higher than that of nonfluorinated copolymer (5.80%) is attributed to the higher values of both J(sc) and FF, related to the higher hole mobility and better exciton dissociation efficiency. Moreover, employing a low boiling point solvent additive, i.e. o-chlorobenzaldehyde (CBA) (boiling point 132 degrees C) for active layer deposition and after the optimization of concentration of CBA, the resulted PSC showed overall PCE of 8.10%, which is higher than the PSC based on active processed with DIO/CB, related to the better balanced charge transport, induced by the fast removal of residues of solvent. To our best of our knowledge, PCE of 8.10% is also the highest for the PSCs with low bandgap of below 1.30 eV. (C) 2017 Elsevier B.V. All rights reserved.

We synthesized an ultra low bandgap terpolymer denoted as P containing fluorinated-fluorene attached thiadiazoloquinoxaline and benzothiadiazole acceptors and thiophene as donor in its backbone and investigated its optical and electrochemical properties. This terpolymer is used for as donor along with PC71BM as electron acceptor in solution processed polymer solar cells (PSCs). The P showed a shows strong absorption band from 650 nm to 1100 nm with an optical bandgap of 1.12 eV and highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of -5.25 eV and -3.87 eV, respectively. After the optimization of P to PC71BM weight ratio, the optimized weight ratio 1: 2 in chlorobenzene (CB) solution, the PSC showed overall power conversion efficiency of 4.10% (J(sc) of 10.96 mA/cm(2), V-oc of 0.68 V and FF of 0.55). After the solvent additive (3 v% DIO) followed by subsequent thermal annealing (SA-TA) the PCE has been increased up to 7.54% with Jsc of 16.12 mA/cm(2), Voc of 0.65 V and FF of 0.72. The increase in the PCE is related with the enhancement in the both Jsc and FF, attributed optimized nanoscale morphology of the active layer for both efficient exciton dissociation and charge transport towards the electrodes and balanced charge transport in the device, induced by the TSA treatment of the active layer. This is the highest PCE of PSCs with an energy loss about 0.47 eV with the low bandgap of 1.12 eV. (C) 2017 Elsevier B.V. All rights reserved.

We report the synthesis of a D-A random terpolymer denoted as P2 consists of one thiophene donor unit and three acceptor benzothiadiazole (BT), pyrrolodithienoquinoxalinedione (PDQD) and thiadiazoloquinoxaline (TDQ) units by Stille-coupling reaction and investigated its optical and electrochemical properties. We have compared its properties with the parent copolymer P1. The P2 exhibits bandgap of about 1.18 eV which is lower than that of P1 (1.50 eV), indicating strength of accepting units controls both the optical and electrochemical bandgap. We have used terpolymer P2 as electron donor along with [6,6]-phenyl C-71 butyric acid methyl ester (PC71BM) as electron acceptor for the fabrication of solution processed bulk heterojunction polymer solar cells (PSCs). PSC based on an optimized P2:PC71BM (1:2 by weight) active layer processed with 3v % DIO/DCB solution, displayed a power conversion efficiency (PCE) of 7.22%, which is higher than that for P1 based polymer solar cell (PCE = 6.56%) processed under same conditions. The higher value of PCE for P2:PC71BM may be related to more favorable phase separated morphology of active layer as compared to P1:PC71BM, beneficial for the exciton dissociation and charge transport, as evidenced from the larger hole mobility. (C) 2016 Elsevier B.V. All rights reserved.

Two ultra low bandgap (Eg ≤ 1.2 eV) D–A copolymers, with UV to near-IR absorption, are synthesized and used as donors for polymer solar cells, obtaining PCEs of 7.27% and 6.68%.

Two D–A copolymers, F1 and F2, with fluorene and thiazole units were substituted, respectively, on a thiadiazoloquinoxaline (TDQ) unit to enhance the electron-accepting strength of TDQ.

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 : PC 71 BM (1: 2, v/v) and P2 : PC 71 BM (1: 1, v/v) have open-circuit voltage V oc , short circuit current J sc , and efficiency of 0.79 and 0.84 V, 8.32 and 9.54 mA/cm 2 , 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 V oc 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 J sc and filling factor.

Two low bandgap D-A1–D-A2 conjugated (with/without fluorine substitution) copolymers, with benzothiadiazole and thiadiazoloquinoxaline acceptors, were used to fabricate BHJ polymer solar cells that achieved up to 7.21% power conversion efficiency.

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 PC 60 BM and PC 70 BM on photovoltaic characteristics was also studied.

CuInS2 and ZnS are miscible so that quaternary ZnS-CuInS2 alloys can be obtained. This opens the possibility to tune optical properties of the material in a wide range via control of the elemental composition. In the present work, ZnS-CuInS2 nanorods were synthesized by means of colloidal chemistry. Their absorption properties were studied in detail, and different types of optical transitions identified. In view of optoelectronic applications, the nanoparticles were examined for their suitability as absorber material in hybrid polymer/nanoparticle solar cells. Therefore, the nanorods were combined with a common low band gap polymer. Cyclic voltammetry and electron spin resonance were used to study the alignment of the energy levels at the heterojunction as well as the possibility of charge transfer. The material combination forms a type II heterojunction, but with the nanoparticles acting as electron donor material. The blends were implemented in hybrid solar cells. Although the photocurrent density and efficiency achieved were relatively low, the system showed a high open-circuit voltage exceeding the value 1 V. (C) 2015 Elsevier B.V. All rights reserved.

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.

Colloidally synthesized CuInS2 nanocrystals are a promising candidate for hybrid solar cell applications due to suitable optical and transport properties of copper indium disulfide and being it an eco-friendly material. However, as opposite to solar cells where CuInS2 is synthesized in situ in a conductive polymer matrix, advances in the field of hybrid solar cells containing colloidal CuInS2 nanocrystals that are blended after synthesis with a polymer are still negligible. Here, we report about the influence of pyridine, alkylamine, and hexanethiol stabilizing ligands on the morphology of the active layer and the electrical characteristics of solar cells based on elongated and pyramidal CuInS2 nanocrystals blended with poly(3-hexylthiophene) (P3HT). All CuInS2 nanocrystals used within this study had a wurtzite crystal structure as revealed by X-ray diffraction. With pyridine as ligand, the morphology was found to depend strongly on the shape of the nanocrystals. Strong agglomeration was observed in the case of elongated nanocrystals and explains the low performance of corresponding solar cells. Employment of hexanethiol as ligand resulted in an improvement of the morphology of the CuInS2/P3HT layers and enhancement of the rectification ratio of the laboratory solar cells. Nevertheless, it was found that morphology of the active layer is not the main limiting factor in the CuInS2/P3HT system. According to cyclic voltammetry measurements, unsuitable alignment of the energy levels for CuInS2 nanocrystals and P3HT was observed. Taking this fact into account, appropriate donor materials for CuInS2 based bulk heterojunctions are discussed.

Alkylamines were recently found to be suitable ligands for CdSe quantum dots with respect to applications in polymer/nanoparticle solar cells. However, the physical origin of the superior performance with respect to more widely used pyridine-capped quantum dots still remains unclear. Here, we report about the details of the surface modification procedure of CdSe quantum dots with alkylamines and subsequent application of the nanoparticles for the fabrication of hybrid CdSe/poly-3-hexylthiophene (P3HT) solar cells. As-synthesized nanocrystals were subjected to a pyridine treatment as an intermediate step to remove the high molecular weight species from the sample, and then the exchanges with octylamine and butylamine were carried out. Investigation based on nuclear magnetic resonance (NMR), X-ray spectroscopy (EDX), and thermal gravimetric analysis (TGA) demonstrated that pyridine ligand exchange as intermediate step is an effective procedure to reduce undesirable impurities which otherwise impede further surface modification and, therefore, the final performance of the CdSe/P3HT hybrid cells. Laboratory samples with butylamine- and octylamine-capped CdSe nanoparticles and P3HT were prepared and characterized by current-voltage (I-V) and external quantum efficiency (EQE) measurements. In order to find out the optimum parameters of the butylamine-capped CdSe/P3HT samples, we looked at the influence of the active layer thickness and annealing temperature on the solar cell performance. Power conversion efficiency (PCE) of 2.0% was reached for butylamine-stabilized CdSe quantum dots and P3HT. The superior performance with respect to pyridine-capped quantum dots was found to be mainly due to a higher photocurrent. Deeper analysis of the photocurrent improvement was performed by detailed comparison of the EQE spectra and investigations on the charge carrier generation and recombination processes by light-induced electron spin resonance (I-ESR). Therefrom, we have done a model based on different charge carrier trap states at the nanocrystal surface.

Colloidal CdSe quantum dots (QDs) are suitable as electron acceptors in polymer/nanoparticle bulk heterojunction hybrid solar cells. For this application, a thick organic ligand shell which is typically surrounding the QDs after synthesis needs to be removed. Ligand exchange with pyridine is the most widely used method for this purpose. Although this approach is already 15 years old, detailed studies on the effectiveness of ligand exchange with pyridine for solar cell applications are still missing. In the present work hybrid solar cells were prepared from CdSe QDs initially capped with oleic acid (OA), and the impact of single and multiple pyridine treatment was thoroughly investigated. NMR was applied to determine the composition of the ligand shell as well as to distinguish the bound and free ligands before and after ligand exchange. It is shown that after a single pyridine treatment some amount of OA is still present in the samples. By using thermal gravimetric analysis (TGA) we could obtain also quan...