High-Performance Inverted Polymer Solar Cells: Study and Analysis of Different Cathode Buffer Layers

Abstract

The effect of different cathode buffer layers on the performance of inverted organic solar cells (OSCs) fabricated with {poly[[2,6'-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7-Th):[6,6]-phenyl-C71-butyric acid methyl} (PC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> BM) as active blend layer is studied using device simulator Silvaco/ATLAS TCAD. The parameters used in the simulations were extracted in fabricated OSCs, using the metal-insulator-metal model, obtaining very good agreement between measured and simulated current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ), open-circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> ), fill factor, and power conversion efficiency (PCE). The enhanced performance observed for devices where either 10 nm of poly[(9,9-bis(3-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene) (PFN), 0.6 nm of lithium fluoride (LiF) layer, or the combination of these two materials, was very well reproduced by simulation. Results indicate that the described procedure can be used to predict the behavior of new buffer layers in OSCs. The PCEs values obtained by simulation were 10.90%, 10.45%, 10.38%, 9.03%, and 7.60% for OSCs with cathode buffer layer consisting of the stack PFN/LiF, PFN, LiF/PFN, LiF and without cathode buffer layer, respectively, which agree well with measured values.