Active layer thickness effect on the recombination process of PCDTBT: PC71BM organic solar cells

作者：Namkoong Gon^*; Kong Jaemin; Samson Matthew; Hwang In Wook; Lee Kwanghee

来源：Organic Electronics, 2013, 14(1): 74-79.

DOI：10.1016/j.orgel.2012.10.025

• Organic solar cells
• Active layer thickness
• PCDTBT
• PC71BM
• Lambert W-function

We investigated the effect of active layer thickness on recombination kinetics of poly [N-9 %26apos;%26apos;-hepta-decanyl-2,7-carbazole-alt-5,5-(4%26apos;,7%26apos;-di-2-thienyl-2%26apos;,1%26apos;,3%26apos;-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) based solar cells. Analysis of the fitted Lambert W-function of illuminated current density-voltage (J-V) characteristics revealed increased recombination processes with increased active layer thicknesses. The ideality factor extracted from PCDTBT: PCBM solar cells continuously increased from 1.89 to 3.88 when photoactive layer thickness was increased from 70 to 150 nm. We found that such increase in ideality factor is closely related to the defect density which is increased with increased photoactive layer thickness beyond 110 nm. Therefore, the different density of defect states in PCDTBT: PCBM solar cells causes the different recombination paths where solar cells with a thicker active layer (%26gt;= 110 nm) are considered to undergo coupled trap-assisted recombination processes while single-defect trap-assisted recombination is dominant for thinner (70-90 nm) PCDTBT: PCBM solar cells. As a result, we found that the optimal efficiencies of PCDTBT: PC71BM solar cells were limited to the active layers between 70 and 90 nm. Particularly, when PCDTBT: PC71BM solar cells were optimized with an active layer thickness of 70 nm, energy conversion efficiency reached 6.5% while an increase in thickness led to the reduction of efficiency to 4.7% at 133 nm but then an increase to 5.02% at 150 nm.

• 出版日期2013-1