Low temperature graphene as interfacial layer in graphene/Si Schottky barrier solar cells
Giuliana Faggio1*, Andrea Gnisci1 Giacomo Messina1
Laura Lancellotti2, Eugenia Bobeico2, Paola delle Veneri2
Theodoros Dikonimos3, Nicola Lisi3
1* DIIES Dept., University “Mediterranea” of Reggio Calabria, 89122 Reggio Calabria, Italy,
2 ENEA, Portici Research Center, P.le E.Fermi 1, 80055 Portici, Naples, Italy
3 ENEA, DTE PCU IPSE, Casaccia Research Centre, Via Anguillarese 301, 00123 Rome, Italy
The interfacial layer in a Schottky barrier solar cell (SBSC) plays an important role in reducing the dark current, blocking the majority carriers injected into the frontal electrode at forward bias, reducing surface recombination velocity and passivating silicon surface . All these effects reflect into an improvement of the device performance. Interfacial layer between the semiconductor and the metal realized with a low thermal budget is highly desirable in solar cell processing technology.
In this work, we realize and test a SBSC based on a heterojunction composed of stacked graphene based layers with different structure and conductivity on n-type crystalline silicon. The carbonaceous films were grown by ethanol chemical vapor deposition on Copper foil at 790°C (non-conductive, graphene based derivative)  and 1070°C (conductive graphene) .
The transfer of the graphene stack was successfully performed by using cyclododecane (C12H24) as supporting, protective material during the Cu etching . Raman spectroscopy was used to characterize graphene quality and thickness.
Two different devices were realized. A first with only a conductive graphene layer on n-Silicon and a second with the non-conductive graphene based derivative interlayer between the conductive one and the Si, acting as barrier. The device with the electrically insulating interlayer exhibits better performances in terms of external quantum efficiency (EQE), evaluated with optical bias, and good power conversion efficiency (PCE) of 5%. In order to increase the power conversion efficiency of such cells, the graphene films were doped with nitric acid vapor HNO3 (70%):H2O=1:1 for few minutes . The doping process increased the work function of the graphene film and had a beneficial effect on its conductivity. The PCE of the cells increases after the treatment by HNO3 and reaches 6.7%.
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