Enhanced efficiency of inverted bulk heterojunction solar cells with embedded silica nanoparticles

Incorporation of nanoparticles in the active layer is one of the possible approaches to improve the efficiency of bulk heterojunction organic solar cells (BHJ OSCs). Here, we have synthesized silica nanoparticles (SiO₂ NPs) using the modified stober method and studied the dispersion of various concentrations of SiO₂ NPs in poly (3-hexylthiophene), [6, 6]-phenyl C₆₁-butyric acid methyl ester (P3HT: PCBM) blend. It was found that the inverted geometry device with concentration of 2 wt% of SiO₂ NPs and having the structure ITO/ZnO (NPs)/P3HT: PCBM: SiO₂ NPs/MoO₃/Al shows a maximum efficiency of 1.95 %, which is more than 32 % larger compared to devices without SiO₂ NPs. UV-Vis absorption measurements suggest that the incorporation of SiO₂ NPs into a P3HT: PCBM blend improves the absorption. This absorption enhancement, supported also by finite difference time domain (FDTD) calculations of Mie scattering, results in the observed efficiency improvement.