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Organic Light Emitting Diode Material Process and Devices Part 5

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Tham khảo tài liệu 'organic light emitting diode material process and devices part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Organometallic Materials for Electroluminescent and Photovoltaic Devices 91 In addition to the blocking effect of the sensitizer O Reagan and coworkers recently found another potential factor that is crucial to determine the charge recombination namely that the dye molecules can form complexes with the redox couple and thus enhance the recombination reaction between electrons in TiO2 and the electrolyte O Regan et al. 2009 . They observed that the presence of an amine AR24 Scheme 6 group in the sensitizer can significantly aggravate the charge recombination because of its strong iodide binding capability Reynal et al. 2008 . In addition they found that the charge recombination of the sensitizer with an lkoxy group K19 was clearly more serious than for the alky sulfide substitute TG6 O Regan et al. 2009a . The difference was attributed to the different complexation capability with iodide of the sensitizer. However up to now the detailed mechanism of the complex is not clear. 5.3 The task to increase the electron injection efficiency To increase the electron injection efficiency of DSSCs it is critical to decrease the distance between the sensitizer acceptor and the TiO2. An effective strategy might be the adoption of multi-anchor units. Tian et al. investigated a series of iridium sensitizers with one or two carboxyl anchor groups. It was found that the efficiency of a sensitizer with two carboxyl units Ir3 Scheme 7 is pronouncedly higher than for a sensitizer with a single carboxyl unit Ir1 Scheme 7 Ning et al. 2009a . Another factor that affects the electron injection efficiency is the non-radiative decay of the sensitizer which results in energy loss. Tian et. al investigated the relationship between the emission quantum yield and the electron injection efficiency of sensitizers Ning et al. 2009a . It was found that the electron injection efficiency is consistent with the luminescence quantum yield of the sensitizer. Since less non-radiative decay guarantees high