A Doublet State Palladium(I) N-Heterocyclic Carbene Complex as a Dopant and Stabilizer for Improved Photostability in Organic Solar Cells

Abstract

The effect of doublet state metalloradical complex in a solar cell inside the common active layer poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PC60BM) is explored. In this work, it is demonstrated that the role of the bis-[1,3-bis-(2,6-diisopropylphenyl)-4,5-dichloroimidazol-2-ylidene]palladium(I) hexafluoridophosphate dopant, [Pd(IPrCl)2][PF6], is crucial because the presence of a stable unpaired electron in the molecule significantly improves the optoelectronic performance of the device. We f the optimal concentration of this molecule in the active layer and demonstrate that the presence of this additive in the active layer helps to significantly improve the morphology of the device. The improvements in optoelectronic and morphological parameters are associated with a remarkable increase in photocurrent generation due to more favorable mechanisms of charge separation at the donor/acceptor (D/A) interfaces of the active layer and reduced recombinations. Moreover, the presence of this additive improves the stability of the unencapsulated solar cell against photochemical degradation produced by sunlight.