Efficient bulk heterojunction solar cells incorporating carbon nanotubes and with electron selective interlayers

Abstract

Here, we demonstrate incorporation of carbon nanotubes (CNTs) in the active layer of donor-acceptor based solar cells and thereby significantly enhanced device performance. In this work, bulk heterojunction solar cells were fabricated with P3HT and PCBM incorporating chemically modified CNTs. Enhanced device performance was achieved for P3HT:PCBM solar cells incorporating a certain amount of modified CNTs in the active layer. P3HT:PCBM bulk heterojunction solar cells were fabricated with a thin interlayer of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> between the active layer and top electrode as a electron selective layer. The TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer also acts as a barrier for shorting and shunting in the device, caused by the presence of metallic CNTs. In the fabricated device, CNTs provide efficient charge transportation path and the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer acts as an electron selective layer. The enhanced device performance with introduction of CNTs is attributed to better charge transportation. Work function of MWNTs is in the range of 4.5~5.1 eV, which is close to valance band of polymer; it signifies possible hole transportation through MWNTs in the active layer. As well as, we have studied affect of MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> as a hole and electron selective interlayer respectively for P3HT:PCBM bulk heterojunction solar cells. Fabricated device with MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer compare to PEDOT:PSS device shows better fill factor and small improve in open circuit voltage thought the short circuit current density was less. The initial degradation of P3HT:PCBM solar cells with MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> interlayer at the respective electrode is reduced that of the device with PEDOT:PSS interlayer.