Networked Conductive Polythiophene/Polyaniline Bottlebrushes with Modified Carbon Nanotubes As Hole Transport Layer in Organic Photovoltaics

Abstract

Three types of hole transport layers (HTLs) were developed based on multi-walled carbon nanotubes (CNTs), including pure CNT thin films, CNT:poly(3-thiophene ethanol) (P3ThEt)-g-polyaniline (PANI) nanocomposites, and CNT-g-poly(3-dodecyl thiophene) (PDDT):P3ThEt-g-PANI interconnected networks, and utilized in poly[benzodithiophene-bis(decyltetradecyl-thien) naphthothiadiazole] (PBDT-DTNT):phenyl-C61-butyric acid methyl ester (PC61BM) and poly[bis(triiso-propylsilylethynyl) benzodithiophene-bis(decyltetradecyl-thien) naphthobisthiadiazole] (PBDT-TIPS-DTNT-DT):PC61BM solar cells. Pure CNTs were not the appropriate candidates for application instead of conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTLs. To tackle this issue, the CNT:P3ThEt-g-PANI and CNT-g-PDDT:P3ThEt-g-PANI films were focused with thicknesses of 10 nm and 20 nm. The prominent characteristics peaked at 20-nm thin films of CNT-g-PDDT:P3ThEt-g-PANI, demonstrating the largest power conversion efficiencies (PCE) of 5.65 (12.84 mA/cm2, 62%, and 0.71 V) and 4.80% (11.59 mA/cm2, 60%, and 0.69 V) in the BDT-DTNT and PBDT-TIPS-DTNT-DT based devices, respectively. The CNT-g-PDDT:P3ThEt-g-PANI thin films which possess an interconnected network, composed of grafted-CNTs and P3ThEt-g-PANI bottlebrushes, were proper alternatives for conventional PEDOT:PSS HTLs and warranted the superior photovoltaic results by smooth morphologies (root mean square = 1.0–1.1 nm) and low sheet resistance (2.2–8.3 × 104 Ω/sq). The corresponding systems without grafting of CNT precursors were the second categories of well-functioned HTLs (3.13–4.04%) and had somehow decreased physical and photovoltaic properties.