Efficiency-limiting processes in cyclopentadithiophene-bridged donor-acceptor-type dyes for solid-state dye-sensitized solar cells

Abstract

The charge generation and recombination processes in three novel push-pull photosensitizers for dye-sensitized solar cells (DSSCs) are studied by ps-μs transient absorption (TA) and quasi-steady-state photoinduced absorption (PIA) spectroscopy. The three cyclopentadithiophene-based photosensitizer dye molecules exhibit comparably low power conversion efficiencies ranging from 0.8% to 1.7% in solid-state DSSCs. We find that the photocurrents increase in the presence of Li-salt additives. Both TA and PIA measurements observe long-lived dye cations created by electron injection from the dyes' excited state for two dyes from the series. However, the third dye shows significantly lower performance as a consequence of the less efficient electron injection even after the addition of Li-salts and faster electron-hole recombination on the ns-μs time scale. In essence, the prerequisites for this class of donor-π bridge-acceptor photosensitizers to reach higher charge generation efficiencies are a combination of strong dipole moments and fine tuning of the electronic landscape at the titania-dye interface by Li-salt addition.

Effect of Electron-Withdrawing/-Donating Groups on the Sensitizing Action of the Novel Organic Dye “3-(5-(4-(Diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic Acid” for N-Type Dye-Sensitized Solar Cells: A Theoretical Study

“…Therefore, the ultrafast transfer of excited electrons to the CBs of the semiconductor is realized to lead to an efficient electron–hole separation and ultimately electricity generation. Since the discovery and successful synthesis of the novel organic dyepolyene–diphenylaniline, also known as D5 , with an overall efficiency of ∼5%, many experimental and theoretical studies have been performed to improve the DSSC performance through appropriate modifications of donor, ,,,− π-spacer, ,,− and acceptor − subunits. Recently, novel organic dyes with a D–A′−π–A configuration including an extra internal acceptor A′ within the traditional D−π–A structure have been introduced.…”

Alkylated Indolo[3,2,1-Jk]carbazoles as New Building Blocks for Solution Processable Organic Electronics

“…[17,18] However, the development of more feasible synthetic approaches based on palladium catalyzed methodologies, [8,19,20] paved the way for the increased use of the ICz scaffold in organic electronics. In recent years the ICz scaffold became especially important as building block in dye sensitized [21][22][23] and perovskite solar cells, [24] and OLEDs. Particularly successful was the application of ICz as integral functional unit in host materials for PhOLEDs [8][9][10][25][26][27] and TADF-OLEDs, [28] but also as building block for fluorescent [12,27,29,30] and TADF emitters.…”

Direct and Energy-Transfer-Mediated Charge-Transfer State Formation and Recombination in Triangulene-Spacer-Perylenediimide Multichromophores: Lessons for Photovoltaic Applications

“…Photoinduced electronic energy transfer (EET) and charge transfer (CT) processes are of key interest in photosynthesis, [1][2][3] photocatalysis, [4][5] organic light emitting diodes, [6][7] organic photovoltaic cells, [8][9][10][11][12][13][14] and many related photophysical phenomena where long-distance charge separation is essential. [15][16][17][18][19] These processes are, however, rather intricate already in simple molecular donor-acceptor type dyads, [20][21][22] where EET can proceed via the CT state, enabling fast energy transfer between the donor and the acceptor units even with orthogonal transition dipoles. 23 Moreover, Förster or Redfield theories, which are successful in describing long-range EET, cannot rationalize it in small molecular dyads with large electronic couplings between the states.…”

“…Photoinduced electronic energy-transfer (ET) and charge-transfer (CT) processes are of key interest in photosynthesis, − photocatalysis, , organic light-emitting diodes, , organic photovoltaic (OPV) cells, − and many related photophysical phenomena where long-distance charge separation is essential. − These processes are, however, rather intricate already in simple molecular donor–acceptor-type dyads, − where ET can proceed via the CT state, enabling fast ET between the donor and the acceptor units even with orthogonal transition dipoles . Moreover, Förster or Redfield theories, which are successful in describing long-range ET, cannot rationalize it in small molecular dyads with large electronic couplings between the states. − The situation is even more complex in symmetric donor–acceptor–donor or acceptor–donor–acceptor triads, where the symmetry of the CT state (quadrupolar vs dipolar) also depends on the strength of the electronic coupling between the donor and acceptor units and stabilization by the environment. , The molecular structure can therefore be used to control the CT mechanism by, for example, varying the length of the conjugated spacer, thereby controlling the coupling between the donor and acceptor in the multichromophore …”