Revealing charge carrier dynamics in squaraine:[6, 6]-phenyl-C 71-butyric acid methyl ester based organic solar cells.

Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM₇₁) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM₇₁ in SQ results in the formation of polaron pairs with ∼550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM₇₁ compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC₇₁ molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM₇₁ but also gives the facts relating to the effect of PCBM₇₁ mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex recombinations in the blend. These findings have been complimented by the charge transport study in the device using impedance spectroscopy. The various important transport parameters are transit time (τ_t), diffusion constant (D_n), global mobility (μ) and carrier lifetime (τ_r). The values of these parameters are 26.38 μs, 4.64x10^-6 cm²s^-1, 6.12x10^-6 cm²V^-1s^-1 and 399 μs, respectively. To the best of our knowledge such study related to SQ is not present in the literature comprehensively. [ABSTRACT FROM AUTHOR]