In operando morphology investigation of inverted bulk heterojunction organic solar cells by GISAXS

Highly stable poly(3-hexylthiophene-2,5-diyl) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells are fabricated by using an inverted geometry. The direct correlation between the morphology of the active layer and the device performance during continuous operation under illumination is revealed by in operando grazing incidence small angle X-ray scattering (GISAXS) and I-V measurements. Other than in devices with normal geometry, it is found that the P3HT : PCBM active layer shows a stable morphology during early operation times, which leads to an improved stability of the short circuit current and accordingly the power conversion efficiency of the inverted solar cell. Furthermore, the inverted P3HT : PCBM solar cells are long-term stable without encapsulation if they are stored under ambient dark conditions. It reveals that the power conversion efficiency preserves around 88% of the initial value after more than 150 days.