Relation of Polymer Degradation in Air With the Charge Carrier Concentration in PTB1, PTB7, and PCBM Layers Used in High-Efficiency Solar Cells

This paper presents the analysis of degradation in metal-insulator-semiconductor (MIS) and metal-semiconductor-metal (MSM) structures based on the polymers poly[[4,8-bis (octyloxy) benzo [1,2-b:4,5-b'] dithiophene-2,6-diyl] [2-[(dodecyloxy) carbonyl] thieno[3,4-b]thiophenediyl]] (PTB1), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl]] (PTB7), and the fullerene [6,6]-phenyl C61-butyric acid methyl ester under air environment (60 ± 5% relative humidity). Capacitance-voltage (C-V) measurement is used to analyze the degradation process during 240 h and its relationship with the carrier concentration to be correlated with its physical mechanisms. The degradation on MIS structures was more stable than that on MSM structures due to the passivation presence by poly(methyl methacrylate) covering the polymer in MIS structures. The analysis on charge carrier concentration permits the identification and evaluation of the intensity of degradation mechanisms over time on devices under air environment, where it is possible to transfer this knowledge to high-efficiency organic solar cells using almost the same materials and structures.