by Allison Kerley
In response to current interest in organic solar cells, W. Li et al. investigated the effectiveness of a new small band gap semiconducting polymer, PMDPP3T, in single, tandem and triple junction solar cells. In single-junction cells PMDPP3T was found to have an external quantum efficiency (EQE) of up to 7.0% when mixed with PCBM. In single-junction solar cells, PMDPP3T was found to absorb radiation closer to the infrared light spectrum than current polymer, absorbing up to 960nm. In multi-junction solar cells, it was found that all solar cells utilizing PMDPP3 in conjunction with PCDTBT, reached efficiencies between 8.4% and 8.9%. In addition, W. Li et al. also found that tandem and triple-junction solar cells, compared to single-junction solar cells of the same layer thickness, were 50-60% more efficient.
Li, W., Furlan, A., Hendriks, K.H., Wienk, M.M., Janssen, R.A., 2013. Efficient tandem and triple-junction polymer solar cells. Journal of the American Chemical Society 135, 5529-5532. http://goo.gl/5eu8U1
Multi-tandem solar cells have multiple layers made up of different compounds, with each compound absorbing a different portion of the visible light spectrum. In their tandem-junction solar cells, W. Li et al. use PMDPP3T combined with PCBM for one layer, and PCDTBT combined with PCBM for the second layer. It was found that PCDTBT and PMDPP3T have complementary absorption spectra, absorbing a different part of the visible light spectrum with little overlap. In their triple-junction solar cells, they used two layers of PMDPP3T combined with PCBM and one layer of PCDTBT combined with PCBM. The tandem-junction solar cells were recorded to have a power conversion efficiency (PCE) of 8.9%, and the triple-junction solar cells had a PCE of 9.6%. In comparison to the single-junction solar cells of the same layer thickness, the tandem and triple-junction solar cells were found to have a 50-60% efficiency increase.
PMDPP3T is shorthand for poly[[2,5-bis(2-hexyldecyl-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[3’,3”-dimethyl-2,2’:5’,2”-terthiophene]-5,5”-diyl]. PCBM is short for [6.6]-phenyl-C71-butric acid methyl ester.