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Influence of Ion Induced Local Coulomb Field and Polarity on Charge Generation and Efficiency in Poly(3‐Hexylthiophene)‐Based Solid‐State Dye‐Sensitized Solar Cells
Author(s) -
Abrusci Agnese,
Santosh Kumar R. Sai,
AlHashimi Mohammed,
Heeney Martin,
Petrozza Annamaria,
Snaith Henry J.
Publication year - 2011
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201100048
Subject(s) - dye sensitized solar cell , materials science , ultrafast laser spectroscopy , excited state , quasi solid , ion , ionic bonding , absorption (acoustics) , solar cell , energy conversion efficiency , photochemistry , lithium (medication) , optoelectronics , chemical physics , electrolyte , spectroscopy , chemistry , organic chemistry , electrode , atomic physics , composite material , physics , quantum mechanics , medicine , endocrinology
Dye‐sensitized solar cells (DSSC) are a realistic option for converting light to electrical energy. Hybrid architectures offer a vast materials library for device optimization, including a variety of metal oxides, organic and inorganic sensitizers, molecular, polymeric and electrolytic hole‐transporter materials. In order to further improve the efficiency of solid‐state dye‐sensitized solar cells, recent attention has focused on using light absorbing polymers such as poly(3‐hexylthiophene) (P3HT), to replace the more commonly used “transparent” 2,2′,7,7′‐tetrakis‐( N , N ‐di‐ p ‐methoxyphenyl‐amine)9,9′spiro‐bifluorene (spiro‐OMeTAD), in order to enhance the light absorption within thin films. As is the case with spiro‐OMeTAD based solid‐state DSSC, the P3HT‐based devices improve significantly with the addition of lithium bis(trifluoromethylsulfonyl)imide salts (Li‐TFSI), although the precise role of these additives has not yet been clarified in solid‐state DSCs. Here, we present a thorough study on the effect of Li‐TFSI in P3HT based solid‐state DSSC incorporating an indolene‐based organic sensitizer termed D102. Employing ultrafast transient absorption and cw‐emission spectroscopy together with electronic measurements, we demonstrate a fine tuning of the energetic landscape of the active cell components by the local Coulomb field induced by the ions. This increases the charge transfer nature of the excited state on the dye, significantly accelerating electron injection into the TiO 2 . We demonstrate that this ionic influence on the excited state energy is the primary reason for enhanced charge generation with the addition of ionic additives. The deepening of the relative position of the TiO 2 conduction band, which has previously been thought to be the cause for enhanced charge generation in dye sensitized solar cells with the addition of lithium salts, appears to be of minor importance in this system.