Combined parametric optimization of P3HT: PCBM films for efficient bulk-heterojunction solar cells

In this report, the effects of photoactive blend compositions, film thicknesses, and annealing conditions on the P3HT:PCBM solar cells performance and reproducibility was investigated. The performance of prepared devices was described by examining their absorption spectra, current-voltage characteristics and external quantum efficiency (EQE). The thickness of active layer was achieved as 190 nm, 125 nm, and 90 nm, by maintaining the spin speed. Current density (J) slightly increases from 6.39 to 7.15 mA/cm with increase in thickness from 90 to 125 nm; however, with further increase in film thickness (190 nm), the J was reduced to 4.39 mA/cm. To optimize the device performance, four different compositions of PCBM (1:0.6, 1:0.8, 1:1, and 1:12) were investigated at the most favorable film thickness ~ 125 nm. The effect of different PCBM compositions on photovoltaic performance was demonstrated by X-ray diffraction (XRD) and Raman measurements that illuminated modification in structural properties. Additionally, annealing condition led to achieve the good phase separation for efficient charge separation and transport within P3HT: PCBM film which further leads to increased efficiency (PCE ~ 3.31%). These effects deliver valued facts for the choices of PCBM amount in P3HT:PCBM system, and this efficient device optimization might be useful in other efficient photovoltaic systems for better performance through excellent reproducibility. [Figure not available: see fulltext.].