Synthesis, optical and electrochemical properties of the A–π-D–π-A porphyrin and its application as an electron donor in efficient solution processed

A conjugated acceptor&ndash;donor&ndash;acceptor (A&ndash;&pi;-D&ndash;&pi;-A) with the Zn-porphyrin core and the di-cyanovinyl substituted thiophene (A) connected at meso positions denoted as VC62 was designed and synthesized. The optical and electrochemical properties of VC62 were investigated. This new porphyrin exhibits a broad and intense absorption in the visible and near infrared regions. Bulk-heterojunction (BHJ) solution processed organic solar cells based on this porphyrin, as electron donor material, and PC71BM ([6,6]- phenyl C71 butyric acid methyl ester), as electron acceptor material, were fabricated using THF and a pyridine&ndash; THF solvent exhibiting a power conversion efficiency of 3.65% and 5.24%, respectively. The difference in efficiencies is due to the enhancement of the short circuit current Jsc and FF of the solar cell, which is ascribed to a stronger and broader incident photon to current efficiency (IPCE) response and a better balanced charge transport in the device processed with the pyridine&ndash;THF solvent</div

A single atom change “switches-on” the solar-to- energy conversion efficiency of Zn-porphyrin based dye sensitized solar cells to 10.5%

In this work we report how crucial is the correct design of the porphyrin sensitizers in Dye Sensitized Solar Cells (DSSCs). Only a single atom change switches-on the efficiency from 2–3% to over 10% under standard measurement conditions. We used the 2,1,3-benzothiadazole (BDT) group, as a p-conjugated linker, for the porphyrin LCVC01, a thiophene moiety for the porphyrin LCVC02 and also the furan group for the LCVC03 porphyrin, as molecular spacers between the BDT fragment and the molecule anchoring group, respectively. These three porphyrins were investigated for their application in DSSC devices. All the devices were characterized and found to achieve a record cell efficiency of 10.5% for LCVC02 but only 3.84% and 2.55% for LCVC01 and LCVC03 respectively. On one hand, the introduction of a thiophene, instead of a furan group, illustrates the importance of introducing a chemical group as a spacer, such as thiophene, between the BDT and the anchoring group. On the other hand, the selection of this group has to be correct because the change of a single atom increases the charge recombination rate and decreases the device performance. These changes can be rationalized by analyzing the dye dipoles and their interactions

Organic-Ruthenium(II) Polypyridyl Complex Based Sensitizer for Dye-Sensitized Solar Cell Applications

A new high molar extinction coefficient organic-ruthenium(II) polypyridyl complex sensitizer (RD-Cou) that contains 2,2,6,6-tetramethyl-9-thiophene-2-yl-2,3,5,6,6a,11c-hexahydro1H,4H-11oxa-3a-aza-benzoanthracene-10-one as extended -conjugation of ancillary bipyridine ligand, 4,4-dicaboxy-2,26,2-bipyridine, and a thiocyanate ligand in its molecular structure has been synthesized and completely characterized by CHN, Mass, 1H-NMR, UV-Vis, and fluorescence spectroscopies as well as cyclic voltammetry. The new sensitizer was tested in dye-sensitized solar cells using a durable redox electrolyte and compared its performance to that of standard sensitizer Z-907

A–p–D–p–A based porphyrin for solution processed small molecule bulk heterojunction solar cells

In this article, we have designed and synthesized a porphyrin with the following molecular architecture A&ndash; p&ndash;D&ndash;p&ndash;A in which ethyl rhodanine end capping groups were linked to the core porphyrin donor via an octyl thiophene-ethynylene p bridge denoted as VC117 and used it as an electron donor along with ([6,6]-phenyl C71 butyric acid methyl ester) (PC71BM) as an electron acceptor for the fabrication of solution processed organic solar cells. The solution processed BHJ organic solar cell with an optimized weight ratio of 1 : 1 VC117 : PC71BM in THF (tetrahydrofuran) showed an overall power conversion efficiency (PCE) of 2.95% with short circuit current Jsc &frac14; 8.34 mA cm_x0002_2, open circuit voltage Voc &frac14; 0.82 V and fill factor FF &frac14; 0.43. Nonetheless, when the active layer of the solar cell was processed from a mixture of 4% v/v of pyridine in THF solvent, it achieved a PCE value of 4.46% and further improved up to 5.50% after thermal annealing. This is ascribed to the enhancement of both the Jsc and FF values. The higher value of Jsc is explained by the increased absorption profile of the blend, the higher incident photon to current efficiency (IPCE) response and the better crystallinity of the active layer when processed with solvent additives and thermal annealing while the enhancement of FF is due to the better charge transport capability and the charge collection efficiency of the latter device.</div

Solution processed organic solar cells based on A– D–D0–D–A small molecule with benzo[1,2-b:4,5-b0] dithiophene donor (D0) unit, cyclopentadithiophene

Solution processed small molecule A&ndash;D&ndash;D0&ndash;D&ndash;A, denoted as BDT(CDTRH)2, consists of 2-ethylhexoxy substituted BDT (donor D&#39; unit) as the central building block and 3-ethylrhodanine (RH) as the end capped terminal (acceptor group) unit, with a p-linkage of cyclopentadithiophene (CDT) (donor D). We have designed and synthesized it, and we have investigated its optical and electrochemical properties, finding that its energy levels are compatible with the energy levels of fullerene derivatives for efficient exciton dissociation. This small molecule has been used as an electron donor along with PC71BM as the electron acceptor for the fabrication of solution processed small molecule bulk heterojunction (BHJ) solar cells. The BHJ solar cell processed with BDT(CDTRH)2 : PC71BM (1 : 1 wt ratio) showed a power conversion efficiency (PCE) of 4.58% with Jsc &frac14; 8.66 mA cm_x0002_2, Voc &frac14; 0.98 V and FF &frac14; 0.54. The high Voc value of the device has been attributed to the deeper HOMO energy level of BDT(CDTRH)2. The overall PCE of the device has been increased up to 6.02% (Jsc &frac14; 10.42 mA cm_x0002_2, Voc &frac14; 0.94 V FF &frac14; 0.62) when the blend was processed with 3% v/v CN/CF solvent. This increase is mainly due to an increase in Jsc and FF, which was linked to the increase in crystallinity and favorable nanomorphology of the active layer improving exciton dissociation and achieving a more balanced charge transport in the device.</div

D‑π‑A Porphyrin Employing an Indoline Donor Group for High Efficiency Dye-Sensitized Solar Cells

Dye-sensitized solar cell (DSC) devices were fabricated using a novel donor-(π bridge)-acceptor (D-π-A) porphyrin sensitizer, <b>VC-70</b>, in which an indoline is linked directly to the porphyrin core and functions as the donor group. The best efficiencies of <b>VC-70</b> and reference <b>YD2-</b><i><b>o</b></i><b>-C8</b> devices were found to be 7.31 and 7.60%, respectively, and AMG 1.5 illumination and device properties were fully characterized using transient absorption, charge extraction, and transient photovoltage techniques. A notable effect on TiO₂ conduction band energetics and electron lifetime was observed following light soaking of <b>VC-70</b> devices under AMG 1.5 illumination. Upon cosensitization of <b>VC-70</b> with the organic dye <b>D205</b> an improved efficiency of 8.10% was obtained

Organic-Ruthenium(II) Polypyridyl Complex Based Sensitizer for Dye-Sensitized Solar Cell Applications

A new high molar extinction coefficient organic-ruthenium(II) polypyridyl complex sensitizer (RD-Cou) that contains 2,2 ,6,6 -tetramethyl-9-thiophene-2-yl-2,3,5,6,6a,11c-hexahydro1H,4H-11oxa-3a-aza-benzoanthracene-10-one as extended π-conjugation of ancillary bipyridine ligand, 4,4 -dicaboxy-2,2 :6 ,2 -bipyridine, and a thiocyanate ligand in its molecular structure has been synthesized and completely characterized by CHN, Mass, 1 H-NMR, UV-Vis, and fluorescence spectroscopies as well as cyclic voltammetry. The new sensitizer was tested in dye-sensitized solar cells using a durable redox electrolyte and compared its performance to that of standard sensitizer Z-907

Solvent Annealing Control of Bulk Heterojunction Organic Solar Cells with 6.6% Efficiency Based on a Benzodithiophene Donor Core and Dicyano Acceptor Units

A novel semiconductor organic molecule, denoted as <b>VC89</b>, having A-D-D1-D-A structure, was synthesized and all relevant physical and chemical features for its application in solar cells were investigated. The structure comprises 2-ethylhexoxy substituted BDT (donor D1 unit) as a core and a dicyano acceptor unit (DCV) as the terminal acceptor group (A) linked through cyclopentadithiophene (CDT) (donor D) moiety. The BHJ OSC <b>VC89</b>:PC₇₁BM (1:2), processed with chloroform (CF) as solvent, showed an overall power conversion efficiency (PCE) of 4.63% with short circuit current <i>J</i>_SC = 9.28 mA/cm², open circuit voltage <i>V</i>_OC = 0.96 V, and fill factor (FF) = 0.52. When the active layer was processed using DIO as a solvent additive (3% v/v in CF), the corresponding solar cell showed a PCE of 6.05% with <i>J</i>_SC = 10.96 mA/cm², <i>V</i>_OC = 0.92, and FF = 0.60. The PCE was further improved to 6.66% with <i>J</i>_SC = 11.68 mA/cm², <i>V</i>_OC = 0.92, and FF = 0.62, when the DIO/CF (3% v/v)-processed active layer was treated with THF vapors (solvent vapor annealing, SVA). The increase in PCE was due to the enhancement in both the <i>J</i>_SC and FF due to the use of the dicyano groups as electron acceptor units. On one hand, <i>J</i>_SC is determined by the enhancement of the film light absorbance, which is reflected in a better IPCE and better charge collection. On the other hand, we show herein that the use of solvent annealing after treatment with chemical additives also leads to better nanomorphologies that substantially improve the solar cell efficiency