Recent advances in the approaches for improving the photovoltaic performance of porphyrin-based DSSCs

Among other photovoltaic techniques including perovskite solar cells and organic solar cells, dye-sensitized solar cells (DSSCs) are considered to be a potential alternative to conventional silicon solar cells. Porphyrins are promising dyes with the properties of easy modification and superior light-harvesting capability. However, porphyrin dyes still suffer from a number of unfavorable aspects, which need to be addressed in order to improve the photovoltaic performance. This feature article briefly summarizes the recent progress in improving the Voc and Jsc of porphyrin-based DSSCs in terms of molecular engineering by modifying the porphyrin macrocycle, donor and acceptor moieties of the porphyrin dyes, coadsorption of the porphrin dyes with bulky coadsorbents like chenodeoxycholic acid (CDCA), and cosensitization of the porphyrin dyes with metal-free organic dyes. Notably, concerted companion (CC) dyes are described in detail, which have been constructed by linking a porphyrin dye subunit and a metal-free organic dye subunit with flexible alkoxy chains to achieve panchromatic absorption and concerted enhancement of Voc and Jsc. In one sentence, this article is expected to provide further insights into the development of high performance DSSCs through the design and syntheses of efficient porphyrin dyes and CC dyes in combination with device optimization to achieve simultaneously elevated Voc and Jsc, which may inspire and promote further progress in the commercialization of the DSSCs.

An Investigation on Gel-State Electrolytes for Solar Cells Sensitized with β-Substituted Porphyrinic Dyes

The presence of a liquid electrolyte in dye-sensitized solar cells (DSSCs) is known to limit the time stability of these devices due to leakage and evaporation phenomena. To overcome this issue, gel-state electrolytes may represent a good solution in order to maintain stability and good performances, albeit at lower costs. In the present work, two different kinds of gel-electrolytes, based on poly (methyl methacrylate) (PMMA) and nanoclay agents, were investigated in DSSC-devices sensitized using β-substituted Zn-porphyrins (namely ZnPC4 and ZnPC12) with enveloping alkoxy chains of different lengths, able to produce a coverage of the photoanode surface. The highest power conversion efficiency (PCE) values equal to 1.06 ± 0.04% and 1.55 ± 0.26% were obtained for ZnPC12 (with longer alkoxy chains) with PMMA- and nanoclay-based electrolytes respectively. The properties of the photoanode/electrolyte interface as well as the influence of the gelling agents on the final properties of the obtained devices were thoroughly characterized.

Synthesis of donor-π-acceptor porphyrins for DSSC: DFT-study, comparison of anchoring mode and effectiveness

In this study two pairs of novel zinc-porphyrin complexes (ZnP1 ZnP2 ZnP3 and ZnP4) were synthesized as sensitizers for DSSC and their photophysical, computational studies and photovoltaic properties were investigated. Structures of proposed dyes are based on a molecular design that relies on donor/[Formula: see text]-bridge/acceptor interactions. Compounds differ by anchoring mode to the titanium dioxide surface: ZnP2 and ZnP4 porphyrins possess carboxyl anchoring groups while ZnP1 and ZnP3 porphyrins have similar structure but without anchors and attached to the surface by isonicotinic acid ligands. All the zinc-porphyrin derivatives bear hexyloxy-chains at the para-positions of their phenyl rings and ZnP3 and ZnP4 contain 1,3,5-triazine fragments as efficient electron transfer bridges. Electron density distribution of the frontier molecular orbitals was calculated based on the density functional theory (DFT). The test DSSC was manufactured and its parameters were measured to compare the effectiveness of the proposed sensitizers. Our results reveal that dyes with an anchoring group directly in their structure demonstrated several times higher efficiency. The use of the triazine fragment proved effective for the introduction of acceptor substituents bearing anchor groups. As a result, the highest efficiency of 4.33% was achieved using the dye ZnP4.

Efficient Sunlight Harvesting by A4 β-Pyrrolic Substituted ZnII Porphyrins: A Mini-Review

Dye-Sensitized Solar Cells (DSSCs) are a highly promising alternative to conventional photovoltaic silicon-based devices, due to the potential low cost and the interesting conversion efficiencies. A key-role is played by the dye, and porphyrin sensitizers have drawn great interest because of their excellent light harvesting properties mimicking photosynthesis. Indeed, porphyrins are characterized by strong electronic absorption bands in the visible region up to the near infrared and by long-lived π^* singlet excited states. Moreover, the presence of four meso and eight β-pyrrolic positions allows a fine tuning of their photoelectrochemical properties through structural modification. Trans-A₂BC push-pull Zn^II porphyrins, characterized by a strong and directional electron excitation process along the push-pull system, have been extensively investigated. On the other hand, A₄ β-pyrrolic substituted tetraaryl Zn^II porphyrins, which incorporate a tetraaryl porphyrinic core as a starting material, have received lower attention, even if they are synthetically more attractive and show several advantages such as a more sterically hindered architecture and enhanced solubility in most common organic solvents. The present contribution intends to review the most prominent A₄ β-substituted Zn^II porphyrins reported in the literature so far for application in DSSCs, focusing on the strategies employed to enhance the light harvesting capability of the dye and on a comparison with meso-substituted analogs.

Porphyrins for Second Order Nonlinear Optics (NLO): An Intriguing History

This short review outlines the main results obtained by our research group over the last 15 years in the field of porphyrins and metal porphyrins for second order nonlinear optics (NLO). This overview aims to provide a general framework of the key factors which affect the second order NLO response of porphyrin chromophores. The pivotal role of the porphyrin ring as π-conjugated linker, the nature of the metal center, the substitution pattern which features the geometrical arrangement of donor and acceptor substituents in the different classes of porphyrin NLO-phores, as well as the aggregation phenomena and the role of solvents are addressed in detail.

Designing Push-Pull Porphyrins for Efficient Dye-Sensitized Solar Cells

Over the past decade, tremendous effort has been made to improve the light-harvesting ability of push-pull porphyrin dyes. Despite notable success achieved in this direction, push-pull porphyrin dyes still suffer from a poor light-harvesting efficiency owing to the lack of absorption between the Soret and Q-bands. To tackle this issue, here we design a series of push-pull porphyrin dyes with anchoring groups either at meso- or β-position using calculations based on first-principles time-dependent density functional theory. In contrast to the common perception, we find that porphyrin dyes bearing an electron-donor at the meso-position and an electron-acceptor at the β-position produce an additional extended band between the Soret and Q-bands appearing at around 500 nm due to S₀ → S₃ excitation, leading to a much higher light-harvesting performances compared to meso- and β-disubstituted ones. In addition, changing the π-conjugated linker at the acceptor site from ethylene linker (C═C) to acetylene linker (C≡C) further improves the light-harvesting ability of meso-β-porphyrin dyes, making them promising candidates for dye-sensitized solar cell application.

4D-π-1A type β-substituted ZnII-porphyrins: ideal green sensitizers for building-integrated photovoltaics

Two novel green β-substituted Zn^II-porphyrins, G1 and G2, based on a 4D-π-1A type substitution pattern have been synthesized. Their enhanced push-pull character, by reduction of H-L energy gaps, promotes broadening and red-shifting of absorption bands. The effective synthetic pathway and the remarkable spectroscopic properties make G2 ideal for BIPV application.

Coupling of Zinc Porphyrin Dyes and Copper Electrolytes: A Springboard for Novel Sustainable Dye-Sensitized Solar Cells

The combination of β-substituted Zn²⁺ porphyrin dyes and copper-based electrolytes represents a sustainable route for economic and environmentally friendly dye-sensitized solar cells. Remarkably, a new copper electrolyte, [Cu(2-mesityl-1,10-phenanthroline)₂]^+/2+, exceeds the performance reached by Co^2+/3+ and I^-/I₃^- reference electrolytes.

Effect of functional groups on sensitization of dye-sensitized solar cells (DSSCs) using free base porphyrins

Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A[Formula: see text]B and A[Formula: see text] free base porphyrin dyes having different functional groups, as sensitizers. The two step synthesis and the effect of different functional groups and their positions on the photosensitization properties of these porphyrin dyes are reported. The highest power conversion efficiencies ([Formula: see text] of 3.26%, 2.94% and 2.84% were achieved for the DSSC fabricated using 5,10,15-tris(4[Formula: see text]-pyridyl)-20-(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]TriPyMCPP), 5,10,15,20-tetrakis(4[Formula: see text]-aminophenyl)porphyrin (H[Formula: see text]TAPP) and 5-(4[Formula: see text]-pyridyl)-10,15,20-tris(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]MPyTriCPP) dyes, respectively. The electron donating amino group is shown to enhance the power conversion efficiency while pyridyl appended porphyrin sensitizers are shown to be superior sensitizers as compared to carboxyphenylporphyrins. The investigation of effect of functional group and position of functional group of porphyrin dye on DSSC can serve as an important tool to guide further selection and synthesis of potential candidates as sensitizers.

Natural α-methylenelactam analogues: Design, synthesis and evaluation of α-alkenyl-γ and δ-lactams as potential antifungal agents against Colletotrichum orbiculare

In our continued efforts to improve the potential utility of the α-methylene-γ-lactone scaffold, 62 new and 59 known natural α-methylenelactam analogues including α-methylene-γ-lactams, α-arylidene-γ and δ-lactams, and 3-arylideneindolin-2-ones were synthesized as the bioisosteric analogues of the α-methylenelactone scaffold. The results of antifungal and cytotoxic activity indicated that among these derivatives compound (E)-1-(2, 6-dichlorobenzyl)-3-(2-fluorobenzylidene) pyrrolidin-2-one (Py51) possessed good selectivity with the highest antifungal activity against Colletotrichum orbiculare with IC₅₀ = 10.4 μM but less cytotoxic activity with IC₅₀ = 141.2 μM (against HepG2 cell line) and 161.2 μM (against human hepatic L02 cell line). Ultrastructural change studies performed by transmission electron microscope showed that Py51 could cause important cell morphological changes in C. orbiculare, such as plasma membrane detached from cell wall, cell wall thickening, mitochondria disruption, a dramatic increase in vacuolation, and eventually a complete loss in the integrity of organelles. Significantly, mitochondria appeared one of the primary targets, as confirmed by their remarkably aberrant morphological changes. Analysis of structure-activity relationships revealed that incorporation of the aryl group into the α-exo-methylene and the N-benzyl substitution increased the activity. Meanwhile, the α-arylidene-γ-lactams have superiority in selectivity over the 3-arylideneindolin-2-ones. Based on the results, the N-benzyl substituted α-(2-fluorophenyl)-γ-lactam was identified as the most promising natural-based scaffold for further discovering and developing improved crop-protection agents.

Effects of Bulky Substituents of Push-Pull Porphyrins on Photovoltaic Properties of Dye-Sensitized Solar Cells

To evaluate the effects of substituent bulkiness around a porphyrin core on the photovoltaic properties of porphyrin-sensitized solar cells, long alkoxy groups were introduced at the meso-phenyl group (ZnPBAT-o-C8) and the anchoring group (ZnPBAT-o-C8Cn, n = 4, 8) of an asymmetrically substituted push-pull porphyrin with double electron-donating diarylamino groups and a single electron-withdrawing carboxyphenylethynyl anchoring group. The spectroscopic and electrochemical properties of ZnPBAT-o-C8 and ZnPBAT-o-C8Cn were found to be superior to those of a push-pull porphyrin reference (YD2-o-C8), demonstrating their excellent light-harvesting and redox properties for dye-sensitized solar cells. A power conversion efficiency (η) of the ZnPBAT-o-C8-sensitized solar cell (η = 9.1%) is higher than that of the YD2-o-C8-sensitized solar cell (η = 8.6%) using iodine-based electrolyte due to the enhanced light-harvesting ability of ZnPBAT-o-C8. In contrast, the solar cells based on ZnPBAT-o-C8Cn, possessing the additional alkoxy chains in the anchoring group, revealed the lower η values of 7.3% (n = 4) and 7.0% (n = 8). Although ZnPBAT-o-C8Cn exhibited higher resistance at the TiO2-dye-electrolyte interface by virtue of the extra alkoxy chains, the reduced amount of the porphyrins on TiO2 by excessive addition of coadsorbent chenodeoxycholic acid (CDCA) for mitigating the aggregation on TiO2 resulted in the low η values. Meanwhile, the ZnPBAT-o-C8-sensitized solar cell showed the lower η value of 8.1% than the YD2-o-C8-sensitized solar cell (η = 9.8%) using cobalt-based electrolyte. The smaller η value of the ZnPBAT-o-C8-sensitized solar cell may be attributed to the insufficient blocking effect of the bulky substituents of ZnPBAT-o-C8 under the cobalt-based electrolyte conditions. Overall, the alkoxy chain length and substitution position around the porphyrin core are important factors to affect the cell performance.