Exciton diffusion length analysis of mixed donor materials in organic solar cells by doping with phosphorescent iridium complex

In this paper, the photovoltaic characteristics of ITO / ( t-bt ) 2 Ir ( acac ) : CuPc (mixed ratio R by weight)/ C 60 /BCP/Ag organic solar cells (OSCs) are analyzed in detail. The intrinsic properties of a ( t-bt ) 2 Ir ( acac ) : CuPc doped layer on device performance are discussed based on theoretical analysis of the experimental OSCs. By studying the photoluminescence densities of pure ( t-bt ) 2 Ir ( acac ) film and mixed films with R = 0.75 , 0.9, the key excitondiffusion lengths L D were calculated to be 28.3 ± 5.0 nm , 31.7 ± 5.0 nm , and 33.0 ± 2.0 nm , respectively. A new method is then proposed to calculate L D for films with R 0.75 . The analysis gives an excitondiffusion length of L D = 17.4 ± 2.5 nm for a mixed film with R = 0.25 , an improvement of 74% in comparison to a pure CuPc layer. Moreover, the excitondiffusion efficiency η E D of an OSC with R = 0.25 is obviously improved with the assistance of an increased excitondiffusion length. Finally, to reveal the influence of the dopant ( t-bt ) 2 Ir ( acac ) on charge carrier collection H ( V ) , device energy loss is analyzed and discussed.

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