Stability of Poly(3-Hexylthiophene):Phenyl-C71-Butyric Acid Methyl Ester Solar Cells Modified by Pre-designed Supramolecular Nanostructures

Abstract

The air stability of poly(3-hexylthiophene) (P3HT):phenyl-C71-butyric acid methyl ester (PC71BM) solar cells and their modified configurations was investigated by pure carbon nanotube (CNT), CNT-g-poly(3-dodecylthiophene) (PDDT) (stem)-P3HT (leaf), CNT-g-P3HT/P3HT butterfly, and core (CNT)-mantle (polyaniline (PANI))-shell (P3HT) nanostructures over a period of 1 month at 5-day intervals. Although the photovoltaic parameters decreased with aging time, the slopes of the decrease were less steep for well-modified systems. The slowest decreasing trends in short-circuit current density (Jsc = 13.41 mA/cm2 to 12.48 mA/cm2), fill factor (FF = 67% to 62%), open-circuit voltage (Voc = 0.69 V to 0.64 V), power conversion efficiency (PCE = 6.20% to 4.95%), and charge transfer resistance (Rtr = 370 Ω cm2 to 688 Ω cm2) plots versus aging were found for the core-mantle-shell modified photovoltaic devices. After 1 month of aging, P3HT:PC71BM:core-mantle-shell solar cells performed even better than 5-day-aged P3HT:PC71BM:stem-leaf photovoltaics (11.94 mA/cm2, 63%, 0.65 V and 4.89%). Orderly packed π-stacks of P3HT backbones in the respective crystals prevented the oxygen and water from penetrating the crystals, and thus the morphology was more stable. Pre-developed nanostructures including CNT-g-P3HT/P3HT butterfly and CNT-g-PANI/P3HT core-mantle-shell supramolecules not only provided higher phase separation in as-prepared devices, but also controlled and stabilized the morphology and constituent arrangement during air aging processes.