ITO‐Free and Flexible Organic Photovoltaic Device Based on High Transparent and Conductive Polyaniline/Carbon Nanotube Thin Films

Abstract

The synthesis and characterization of thin fi lms of polyaniline/carbon nanotubes nanocomposites is reported, as well as their utilization as transparent electrodes in ITO-free organic photovoltaic devices. These fi lms are generated by interfacial synthesis, which provides them with the unique ability to be deposited onto any substrate as transparent fi lms, thus enabling the production of fl exible solar cells using substrates like PET. Very high carbon nanotube loadings can be achieved using these fi lms without signifi cantly affecting their transparency ( ≈ 80-90% transmittance at 550 nm). Sheet resistances as low as 300 Ω / ᮀ are obtained using secondary polyaniline doping in the presence of carbon nanotubes. These fi lms present excellent mechanical stability, exhibiting no lack in performance after 100 bend cycles. Flexible and completely ITO-free organic photovoltaic devices are built using these fi lms as transparent electrodes, and high effi ciencies (up to 2.27%) are achieved.

All-Carbon Electrodes for Flexible Solar Cells

“…As for the G-G cell, its performance is close to that of its G-ITO counterpart, showing the great potential of graphene to substitute the traditional metal grid. Moreover, the current densities of devices with all-carbon electrodes are comparable to those of devices based on an organic active layer with electrodes made of carbon-based and standard materials [29,31,33,45,48,56]. These results suggest that all-carbon electrodes composed of CNT and graphene films could efficiently collect and transport charge carriers towards an external circuit.…”

“…They inspire scientists to attempt to collect them to assembly all-carbon optoelectronic devices, including photodetectors [4,5] and photovoltaics [6][7][8][9][10][11][12][13][14][15][16], which have many potential advantages, such as low cost, simple processing, and long-term stability. Currently, in the field of photovoltaics, carbon nanomaterials are mainly employed as additives [17][18][19][20][21][22][23] or transparent electrodes [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Organic photovoltaics (OPVs) have special advantages including light weight, good flexibility, convenient fabrication, and large-area feasibility, which make them versatile in niche places unfit for Si-based inorganic solar cells, such as power-generating windows and flexible electronic devices [39,40].…”

“…In 2006, Rowell et al used printed films of single-walled carbon nanotube networks on plastic as transparent and flexible anodes of OPVs with a power conversion efficiency (PCE) close to the performance of its ITO/glass counterpart [42]. CNT films produced by chemical vapor deposition (CVD) [31,43], polyaniline interfacial polymerization [29], and brush-painting [44] were also employed as anodes for building ITO-free OPVs, showing more flexible properties than their ITO-based counterparts. Meanwhile, researchers also tried to apply graphene as anodes.…”

Flexible and Semitransparent Organic Solar Cells

“…The high flexibility of the CNTs-based flexible electrode was further confirmed by Geng et al [93] The CNTs solutions were prepared by using sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) surfactants, and the resultant CNTs films were mechanically robust showing no tendency to delaminate from the underlying substrate during routine handling. Recently, Salvatierra et al [94] developed a CNTs/polyaniline (PANI) hybridized film, where the PANI film was polymerized on the surface of self-assembled CNTs (see Figure 5a). The resultant hybrid film was further doped by camphorsulfonic acid and exposure to meta-cresol solvent, leading to a reduced sheet resistance from 85 kΩ sq −1 to 295 Ω sq −1 with the transmittance of ≈90% at 550 nm.…”

Nanoestruturas de carbono (nanotubos, grafeno): Quo Vadis?

“…43 Estes dispositivos são construídos baseados tanto em nanotubos individuais (embora as dificuldades na preparação de nanotubos de paredes simples com o rigoroso controle de quiralidade, aliado ao alto preço deste tipo de nanotubo, seja um limitante importante para viabilização de produção em larga escala), como em arranjos de nanotubos; nanotubos de paredes múltiplas também são candidatos a substituir o cobre em conexões em placas e dispositivos em microeletrônica, diminuindo as perdas e aumentando a capacidade de corrente; 17 nanotubos também estão associados como materiais para dissipar calor em circuitos eletrônicos. Com relação ao grafeno, talvez a aplicação em eletrônica, principalmente em FET, seja a mais próxima de uma aplicação real, utilizando-se grafeno crescido por CVD como componente ativo; 44 v) filmes finos: uma das aplicações mais divulgadas nos últimos anos para nanotubos de carbono, grafeno e seus diferentes nanocompósitos (incluindo com polímeros condutores e nanofios metálicos) está na preparação de eletrodos transparentes condutores, visando substituir o ITO (óxido de índio dopado com óxido de estanho), para utilização em touch screens, LED´s e OLED's, células solares flexíveis, entre outros; [45][46][47] filmes para recobrimento e proteção anti-corrosão também encontram forte apelo de aplicação para estes materiais; 17 vi) meio ambiente: diversas aplicações de nanotubos de carbono em processos de purificação e descontaminação de águas (filtros e membranas), 48 ou como foto-e eletro-catalisador para oxidação de contaminantes vêm sendo reportados; 49 vii) catálise: nanotubos de carbono e grafeno são materiais ideais para suporte de catalisadores (óxidos, metálicos ou mesmo moleculares); várias reações são também catalisadas pelo próprio nanotubo ou grafeno. 50 Os pontos brevemente sumarizados nos parágrafos anteriores correspondem a uma fração das aplicações em potencial destes materiais.…”