A study of donor/acceptor interfaces in a blend of P3HT/PCBM solar cell: Effects of annealing and PCBM loading on optical and electrical properties

• Reduction in PCBM peak absorption intensity is associated with formation of PCBM clusters.
• Effect of annealing on peak absorption is more prominent for highest PCBM loading.
• Annealing at glass transition temperature result in recrystallization of P3HT polymer chains.
• The highest PCBM loading resulted in higher Jsc and better device performance.

Optical, structural and electrical properties based on blend of P3HT: PCBM thin films have been investigated for several PCBM loading whilst exposed to air. Experimental evidence indicates that the peak absorption for PCBM with highest loading concentration show greater reduction in intensity upon annealing temperature of 175 °C. This provides useful information regarding PCBM segregation associated with annealing process. Comparison of GIXRD patterns indicates an increase in intraplanar d spacing and polymer grain size upon thermal annealing. Variation in open circuit voltage and short circuit current with annealing temperatures, suggests that the latter remains almost constant up to around 100 °C and improves gradually with temperature thereafter, whilst the former improves with temperature and the onset of deterioration in current density is linked to percentage PCBM loading. These results are further explained or supported by optical absorption spectroscopy to account for PCBM clustering. A power conversion efficiency of 3.38% was achieved at 175 °C for devices fabricated and tested in air.