Effects of phthalocyanine nanostructure on photovoltaic performance of its polymer composite thin films

Abstract

In this work, nanocomposite polymer solar cells with PEDOT:PSS/PTB7-Th:ITIC:MPc/Al were developed. A PTB7-Th:ITIC bulk heterojunction films doped with metal phthalocyanine nanoribbons were prepared by simple spin-coating methods from chlorobenzene solution. Phthalocyanine nanoribbons were synthesized by a temperature gradient physical vapor deposition method at temperature of 440–470 °C and an argon flow rate in the reaction zone of 150 cm3/min. The loading concentration of phthalocyanine nanoribbons in the PTB7-Th:ITIC mixture was 0.5%. The surface morphology of samples were probed by an atomic force microcopy (AFM). It was found that the surface roughness (Rq) of the PTB7-TH:ITIC photoactive layer decreases approximately two times after doping with phthalocyanine nanoribbons. The absorption spectra of composite films are measured and it was found that the incorporation of phthalocyanine nanoribbons into the PTB7-Th:ITIC photoactive layer leads to the broadening of the optical spectrum and to an increase in the optical density at the absorption maximum by a factor of 1.6. I–V characteristic of PEDOT:PSS/PTB7-Th:ITIC:MPc/Al composite organic solar cells were measured. According to the I–V characteristic, doping of the PTB7-Th:ITIC photoactive layer with phthalocyanine nanoribbons increased the short-circuit current density by 12% and boosted power conversion efficiency by to 4.82% versus an undoped device. In order to understand the effect of phthalocyanine doping on charge transport dynamics, the impedance spectra of composite organic solar cells were measured. An analysis of impedance spectra showed that doping of the photoactive layer with phthalocyanine nanoribbons led to an increase in the effective diffusion length (Deff) of charge carriers by a factor of 3.2 and an increase in the mobility of charge carriers (μ) by a factor of 1.4. The quantum efficiency of composite organic cells was measured and it was revealed that the doping of the photoactive layer with phthalocyanine nanoribbons boosted the quantum efficiency by 4%.