An investigation of the function of an indolene-based organic dye, termed D149, incorporated in to solid-state dye-sensitized solar cells using 2,2',7,7'- tetrakis(N,N-di-p-methoxypheny-amine)-9,9' - spirobifluorene (spiro-OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented. under low light levels, with the solar cells delivering up to 70% incident photon-to-current efficiency (IPCE) and over 6% power conversion efficiency as measured under simulated air mass (AM) 1.5 sun light at 1 and 10 mW cm(-2). However, a considerable nonlinearity. in the photocurrent as intensities approach "full sun" conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100 mW cm(-2). The influence of dye-loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, tune-correlated single-photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data ! suggest that electron transfer from the photoexcited sensitizer into the TiO2 is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro-OMeTAD dominates the charge generation process: A persistent dye bleaching signal is also observed and assigned to a remarkably high density of electrons "trapped" within the dye phase, equivalent to 1.8 x 10(17) cm(-3) under full sun illumination. it is believed that this localized space charge build-up upon the sensitizer is responsible for the non-linearity of photocurrent with intensity and nonoptimum solar. cell performance under full sun conditions.
Christophe Ballif, Aïcha Hessler-Wyser, Quentin Thomas Jeangros, Christian Michael Wolff, Daniel Anthony Jacobs, Austin George Kuba, Mostafa Rabie Shlaly Bahr Othman, Beat Ruhstaller, Anaël Morgane Jaffrès
Michael Graetzel, Shaik Mohammed Zakeeruddin, Felix Thomas Eickemeyer, Peng Wang, Ming Ren