Influence of the fullerene acceptor derivative on the structure, molecular interaction and optoelectronic properties of poly(3-hexylthiophene) blend films: Elucidating key factors

Abstract

Blend films made of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) with the weight ratio in the range of 1:0 to 1:2 were prepared using the spin coating method. The influence of PC71BM on the structure, morphology and molecular interactions was assessed using the AFM, XRD, and FTIR spectroscopy measurements. The optical absorbance spectrum of the P3HT:PC71BM blend films inspected that the band gap of P3HT decreased from 2.1 eV to around 1.95 eV with increasing the amount of PC71BM in P3HT. The luminescence spectra of the P3HT:PC71BM blend films indicated that the incorporation of PC71BM with the P3HT:PC71BM weight ratio above 1:1.2 leads to the low emission, implying that 1:1.2 is the optimal blend ratio. The time dependent luminescence intensity measurements showed that the incorporation of PC71BM in P3HT delays the recombination process, thus, allowing an enhancement of the separation of the photo-generated charges. The electrical behavior of the P3HT:PC71BM blend films is described by the space charge limited conduction mechanism, in particular, the Poole-Frenkel conduction mechanism. The inclusion of the Cd0.95Hf0.05S QDs into the hole transport layer PEDOT:PSS leads to an improvement of the solar cell performance. At optimum PC71BM concentration, the highest conversion efficiency of 4.7% with VOC = 0.62 V and JSC = 4.2 mA cm−2 was attained.