Heterogeneity in Dye鈥揟iO2 Interactions Dictate Charge Transfer Efficiencies for Diketopyrrolopyrrole-Based Polymer Sensitized Solar Cells

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• 作者：Ajay Jha ; Vineeth B. Yasarapudi ; Hadiya Jasbeer ; Catherine Kanimozhi ; Satish Patil ; Jyotishman Dasgupta
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：December 26, 2014
• 年：2014
• 卷：118
• 期：51
• 页码：29650-29662
• 全文大小：521K
• ISSN：1932-7455

文摘

Power conversion efficiency of a solar cell is a complex parameter which usually hides the molecular details of the charge generation process. For rationally tailoring the overall device efficiency of the dye-sensitized solar cell, detailed molecular understanding of photoinduced reactions at the dye-TiO₂ interface has to be achieved. Recently, near-IR absorbing diketopyrrolopyrrole-based (DPP) low bandgap polymeric dyes with enhanced photostabilities have been used for TiO₂ sensitization with moderate efficiencies. To improve the reported device performances, a critical analysis of the polymer鈥揟iO₂ interaction and electron transfer dynamics is imperative. Employing a combination of time-resolved optical measurements complemented by low temperature EPR and steady-state Raman spectroscopy on polymer鈥揟iO₂ conjugates, we provide direct evidence for photoinduced electron injection from the TDPP-BBT polymer singlet state into TiO₂ through the C鈺怬 group of the DPP-core. A detailed excited state description of the electron transfer process in films reveals instrument response function (IRF) limited (<110 fs) charge injection from a minor polymer fraction followed by a picosecond recombination. The major fraction of photoexcited polymers, however, does not show injection indicating pronounced ground state heterogeneity induced due to nonspecific polymer鈥揟iO₂ interactions. Our work therefore underscores the importance of gathering molecular-level insight into the competitive pathways of ultrafast charge generation along with probing the chemical heterogeneity at the nanoscale within the polymer鈥揟iO₂ films for optimizing photovoltaic device efficiencies.