Hafnium metallocene compounds used as cathode interfacial layers for enhanced electron transfer in organic solar cells
1 Department of Physics, Brain Korea 21 Physics Research Division, and Institute of Basic Science, Sungkyunkwan University, Suwon, 440-746, Republic of Korea
2 Department of Chemical Engineering, Sungkyunkwan University, Suwon, 440-746, Republic of Korea
3 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, 440-746, Republic of Korea
4 Department of Chemistry and Institute of Basic Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea
Nanoscale Research Letters 2012, 7:74 doi:10.1186/1556-276X-7-74Published: 9 January 2012
We have used hafnium metallocene compounds as cathode interfacial layers for organic solar cells [OSCs]. A metallocene compound consists of a transition metal and two cyclopentadienyl ligands coordinated in a sandwich structure. For the fabrication of the OSCs, poly[3,4-ethylenedioxythiophene]:poly(styrene sulfonate), poly(3-hexylthiophene-2,5-diyl) + [6,6]-phenyl C61 butyric acid methyl ester, bis-(ethylcyclopentadienyl)hafnium(IV) dichloride, and aluminum were deposited as a hole transport layer, an active layer, a cathode interfacial layer, and a cathode, respectively. The hafnium metallocene compound cathode interfacial layer improved the performance of OSCs compared to that of OSCs without the interfacial layer. The current density-voltage characteristics of OSCs with an interfacial layer thickness of 0.7 nm and of those without an interfacial layer showed power conversion efficiency [PCE] values of 2.96% and 2.34%, respectively, under an illumination condition of 100 mW/cm2 (AM 1.5). It is thought that a cathode interfacial layer of an appropriate thickness enhances the electron transfer between the active layer and the cathode, and thus increases the PCE of the OSCs.