Indolizine‐Based Donors as Organic Sensitizer Components for Dye‐Sensitized Solar Cells

Abstract

Strong electron‐donating functionality is desirable for many organic donor‐π‐bridge‐acceptor (D‐π‐A) dyes. Strategies for increasing the electron‐donating strength of common nitrogen‐based donors include planarization of nitrogen substituents and the use of low resonance‐stabilized energy aromatic ring‐substituted nitrogen atoms. Organic donor motifs based on the planar nitrogen containing heterocycle indolizine are synthesized and incorporated into dye‐sensitized solar cell (DSC) sensitizers. Resonance active substitutions at several positions on indolizine in conjugation with the D‐π‐A π‐system are examined computationally and experimentally. The indolizine‐based donors are observed to contribute electron density with strengths greater than triarylamines and diarylamines, as evidenced by UV/Vis, IR absorptions, and oxidation potential measurements. Fluorescence lifetime studies in solution and on TiO2 yield insights in understanding the performance of indolizine‐based dyes in DSC devices.

Facile synthesis of indolizines using layered double hydroxides@poly(p‐phenylenediamine) as a catalyst with a green tool (neat technology)

“…This catalyst allows the synthesis of indolizines at a temperature of over 120°C and a period of 18 h . Benzylated indolizines were synthesized using Pd 2 (dba) 3 catalyst under reflux conditions with dimethylformamide (DMF) solvent for 16 h . Also, various indolizines have been synthesized through one‐pot, two‐step 1,3‐dipolar cycloadditions in recyclable [Omim]Br with high yields and a broad substrate scope .…”

Molecular Design Principles for Near‐Infrared Absorbing and Emitting Indolizine Dyes

“…For sensitizers bearing the common donor–π‐bridge–acceptor ( D –π–A) architecture, improvement in the donor subunit has been a driving force in the development of high performance sensitizers . Most all‐organic sensitizers with >10 % efficiency utilize phenylamine donor subunits as either triphenylamine or indoline.…”

A low recombination rate indolizine sensitizer for dye-sensitized solar cells

“…While these amine donors are considered "strong" electron donors, the development of groups with increased electron donating strengths while maintaining dye stability is desirable for achieving ideal sensitizer bandgaps with many πbridges and acceptors. [16][17][18] A landmark milestone is set for efficient photon conversion up to 1000 nm, and several sensitizers are already demonstrating the viability of utilizing lower energy photons. [19][20][21][22][23][24][25] Narrowing the sensitizer bandgap to near-ideal levels requires the minimization of non-productive, power-diminishing electron transfer events such as recombination of already-injected electrons with the oxidized redox shuttle or dye.…”

“…To this end, we recently described a series of donor subunits based on indolizine, which was found to be a very strong donor relative to aryl amine donors. 16 The reported indolizine donors (such as AH3) show good performance in model systems especially given the lack of recombination pathways reducing features in the dye designs. Below, we report the synthesis of a heavily alkylated indolizine donor (AH7) with good TiO 2 surface blanketing to lower recombination ( Figure 1).…”

“…The E (S+/S*) potential was calculated to be lowest for AH7 when compared with D35 and AH3, which was attributed to synergistic band-gap narrowing due to competing local aromaticity (proaromaticity) present in the indolizine subunit excited-state as previously reported. 16,31 All dyes were observed to have suitable oxidation potentials to function as DSC sensitizers with driving forces for electron injection and dye regeneration estimated to be adequate for AH7, which has the lowest driving forces for electron transfers when compared with each dye (~430 mV for injection and ~310 mV for regeneration with Co(bpy) 3 ).…”