Effect of n-dodecylthiol and thermal annealing on the performance of P3HT/PC70BM polymer photovoltaic cells

In this research, n-dodecylthiol was added to poly(3-hexylthiophene)/[6,6]-phenyl-C71-butyric acid methyl ester (P3HT/PC70BM) polymer solar cells to improve the crystallinity of P3HT and enhance the phase separation of P3HT/PC70BM. UV-Vis and external quantum efficiency results showed enhancement in P3HT self-organisation ability which led to improved crystallinity and intensified phase separation of P3HT/PC70BM in the cast films. Atomic force microscopic analysis showed that adding n-dodecylthiol to P3HT/PC70BM resulted in an increase in surface roughness which provided more space for P3HT crystallites to form. X-ray diffraction and differential scanning calorimetry analysis showed a higher crystallinity in the heat-treated samples containing up to 2% of n-dodecylthiol by volume, which resulted in a nearly 33% increase in device efficiency at the optimum annealing conditions of 150 degrees C for 30 min. The cell performance deteriorated abruptly at temperatures higher than 150 degrees C.