Efficient donor-acceptor polymer solar cells with controlled nano structure and morphology

Abstract

The photovoltaic devices based on conjugated polymers with semi-conducting properties have received considerable attention from industrial companies and academic research groups because of their possibility of cost-effective fabrication, light-weight, and mechanical flexibility. However, low devices efficiency and durability comes from low conductivity and non-ohmic contact between organic layer are the obstacles to be commercialized. In this point of view, the control of nano-morphology and structure can be an effective way to solve these problems. In this thesis, efficient photovoltaic devices were fabricated by control of nano-morphology and nano-structures in various novel methods.

In chapter 2.1, a patterned conducting IZO film with well-ordered periodic dot-structures with 50 nm or 200 nm deep features has been constructed by nanoimprinting technique as the anode of an organic solar cell. The use of the patterned anode leads to an increase in the short circuit current (Jsc) from 7.03 to 8.94 mA/cm2 and the power conversion efficiency (PCE) from 1.05 to 1.71 % compared to the flat anode. The open circuit voltage (Voc) is also affected by nano-patterned structure. The PCE is also influenced by the aspect ratio of the pattern structure.

In chapter 2.2, flexible bulk-heterojunction polymer solar cells based on poly[N-9"-hepta-decanyl-2,7-carbazole]-alt-5,5-(4`,7`-di-2-thienyl-2`,1`,3`-benzothiadiazole) (PCDTBT) / [6,6]-phenyl C70 butyric acid methyl-ester (PC70BM) were successfully fabricated by a simple nano-imprinting technique. A nano-patterned conducting indium zinc oxide (IZO) with highly ordered periodic dot structures with 50 nm vertical features has been constructed by an imprinting process as the anode of a solar cell on the polycarbonate (PC) flexible substrate. The use of well-ordered patterned IZO anodes led to improved light absorption from a light trapping or scattering effect and increased the interfacial contact area between the anode and ...