Vertically graded organic photovoltaic cells using alternative intermittent electrospray co-deposition

We investigated an alternative intermittent electrospray co-deposition method for solution processed-organic photovoltaic cells with the graded active layer. This method uses separated two solutions, which contain poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61 butyric acid methyl ester (PCBM), are alternatively deposited by using the pulse high voltage. Thus, the P3HT:PCBM blend thin film can be deposited even though a vacuum free experimental setup. The optimized pulse width was found to be > 6 s to avoid unexpected charge to the adjacent glass capillary, which cases the instable electrospray. The P3HT:PCBM ratio of deposited thin film can be controlled by changing the ratio of pulse width for P3HT and PCBM solutions. Finally, a vertically graded bulk heterojunction structure with P3HT:PCBM was successfully demonstrated, leading to a maximum photoconversion efficiency (PCE) of 3.1%. This value was 1.4-fold compared to the uniformly blended device due to the high carrier collection efficiency.