###### Abstract  
The search for novel solar cells designs as an alternative to standard silicon solar cells is important for the future of renewable energy production. One such alternative design is the carbon nanotube/silicon (CNT/Si) heterojunction solar device. In order to improve the performance of large area CNT/Si heterojunction solar cells, a novel organic material, 4,10-_bis_(bis_(4-methoxyphenyl)amino)naptho[7,8,1,2,3-_nopqr_]tetraphene-6,12-dione (DPA-ANT-DPA (shortened to DAD)), was added as an interlayer between the CNT film and the silicon surface. The interlayer was examined with SEM and AFM imaging to determine an optimal thickness for solar cell performance. The DAD was shown to improve the device performance with the efficiency of large area devices improving from 2.89% \(\pm\) 0.40% to 3.34% \(\pm\) 0.10%. solar cells; hole transport layers; organic conductors; thin films +
Footnote †: journal: Applied  
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Footnote 1: College of Science and Engineering, Flinders University, 5042 Adelaide, Australia;  
[EMAIL_ADDRESS] (T.G. ); [EMAIL_ADDRESS] (C.T.G. ); [EMAIL_ADDRESS] (J.G.S.) 2
Footnote 2: Institute of Future Environment and School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT), 2 George Street, 4001 Brisbane, Australia; [EMAIL_ADDRESS]  
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(HTM) 2,2',7,7\"-tetrakis(N,N'-di-\(p\)-methoxyphenylamine)-9,9'-spirobifluorene, more commonly known as spiro-OMeTAD, [6] which is the most commonly used interfacial HTM currently employed in perovskite-based solar cells. [7] Spiro-OMeTAD was found to improve the performance of CNT/Si cells [6]. However, there are downsides to the use of this material. First, the HTM requires a dopant to improve the conductivity to be used in a solar cell architecture and the effect of this dopant is not stable or long-lasting in ambient conditions [8]. Additionally, spiro-OMeTAD is a very expensive material limiting its use in large scale industrial procedures. Thus, it is important to search for cheaper materials which can be applied as alternative HTMs and do not require a degradable doping step, as well as furthering the search for HTMs with superior capabilities. In the search for new HTMs one potential set of candidates involve anthanthrone dye-based systems. The molecule used in this research consists of the anthanthrone dye molecule (ANT) with two functionalized diphenylamine (DPA) end caps. Together the molecule is referred to hereafter as DPA-ANT-DPA. This molecule was synthesized by [PERSON] et al. in 2017 for use as an HTM in perovskite solar cells [9]. The advantage of this molecule over more familiar chemical interlayers (such as Spiro-OMeTAD) is that DPA-ANT-DPA is cheaper and it does not require a dopant. The molecule has a donor-acceptor-donor structure and is produced via a one-step synthesis from relatively cheap components. Thus, DPA-ANT-DPA is a simpler and possibly longer lasting interlayer chemical than some other alternatives. This material, once dissolved in an organic solvent, can simply be coated onto a substrate in atmospheric conditions in order to produce a thin, dopant free, hole-transporting layer. In the perovskite system, interlayer materials of this sort have been shown to provide similar benefits to device performance as Spiro-OMeTAD [9] with the advantage that the material can be prepared for spin coating in ambient conditions. Similar hole transporting materials have been applied to small area CNT/Si heterojunction devices [10]. These materials are 4,4'-(naphthalene-2,6-diyl)_bis_(N,_N-bis_(4-methoxyphenyl)aniline) (NAP), and (E)-4',4\"-etene-1,2-diyl)_bis_(_N,_N-bis_(4-methoxyphenyl)]-[1\",1\"-biphenyl]-4-amine) (BPV).