A cost-effective commercial soluble oxide cluster for highly efficient and stable organic solar cells†
Abstract
Solution-processed phosphomolybdic acid (PMA) was investigated as a hole extraction layer for organic solar cells without any post-annealing processes. PMA is a stable, cost-effective, and commercial soluble oxide cluster, which dramatically simplifies the device fabrication process as well as reduces the cost. The PMA-based device with an active layer of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexl)carbonyl]thieno [3,4-b]thiophenediyl]] (PTB7) mixed with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) achieved a power conversion efficiency (PCE) as high as 8.32% compared with 7.46% for an evaporated MoO3 (e-MoO3)-based device. Transient electrical output characteristics, optical measurements as well as scanning Kelvin probe microscopy were utilized to investigate the improvement in the performance of the device. The results indicated that the enhanced PCE was due to suppressed charge recombination as well as an improved optical path across the device, which led to an enhanced short-circuit current density and fill factor. In addition, the PMA-based device displayed improved long term stability in ambient conditions compared to the e-MoO3-based device.