Abstract
In this work, we present the fabrication and characterization of bulk-heterojunction solar cells on monolayer graphene (MLG) with nickel-grids (Ni-grid) as semitransparent conductive electrode. The electrodes showed a maximum transmittance of 90% (calculated in 300–800 nm range) and a sheet resistance down to 35 Ω/□. On these new anodes, we fabricated TCO free BHJ-SCs using PTB7 blended with PC70BM fullerene derivative as active layer. The best device exhibited a power conversion efficiency (PCE) of 4.2% in direct configuration and 3.6% in inverted configuration. The reference solar cell, realized on the ITO glass substrate, achieved a PCE of 6.1% and 6.7% in direct and inverted configuration respectively; for comparison we also tested OSCs only with simple Ni-grid as semitransparent and conductive electrode, obtaining a low PCE of 0.7%. The proposed approach to realize graphene-based electrodes could be a possible route to reduce the overall impact of the sheet resistance of this type of electrodes allowing their use in several optoelectronic devices.
Highlights
In the last two decades, organic solar cells (OSCs) have seen a growing interest in photovoltaic research due to their versatility as printable low-cost electronics with low weight, flexibility, low temperature processing, large area coating and roll-to-roll applicability coupled with high power conversion efficiency (PCE) [1]
We report the application of monolayer graphene (MLG) coupled with nickel (Ni)-grids on quartz substrates
The direct and the inverted architectures have been realized on MLG transferred on Ni grids and, thanks to the very low contact sheet resistance of Ni to graphene, the devices reached a maximum PCE of 4.2% and 3.6%, respectively, showing the possibility to use Ni/graphene as an efficient electrode for OSCs
Summary
In the last two decades, organic solar cells (OSCs) have seen a growing interest in photovoltaic research due to their versatility as printable low-cost electronics with low weight, flexibility, low temperature processing, large area coating and roll-to-roll applicability coupled with high power conversion efficiency (PCE) [1]. (ii) high cost due to the deposition techniques (sputtering, pulsed laser deposition and electroplating, etc.), (iii) high temperature processing, (iv) high mechanical brittleness and (v) low transparency in the violet region [6,7] For these reasons, several materials, such as conductive polymers, carbon nanotubes, silver nanowires, metal grids and graphene, have been investigated as alternative TCO for photovoltaic applications [8–12]. Graphene films synthesized by thermal CVD were transferred on top of Ni-grids that were realized with a specific geometric profile to avoid cracks in the thin graphene layers and were used as transparent anode to fabricate OSCs. The direct and the inverted architectures have been realized on MLG transferred on Ni grids and, thanks to the very low contact sheet resistance of Ni to graphene, the devices reached a maximum PCE of 4.2% and 3.6%, respectively, showing the possibility to use Ni/graphene as an efficient electrode for OSCs
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