Fabrication Parameter Optimization for a Multilayer Photovoltaic Cell Based on the Heterojunction: Zinc(II)-Meso-Tetrakis(4-Bromophenyl) Porphyrins/Fullerenes

Abstract

The photoelectric properties of multilayer organic photovoltaic cells (OPV cells) were studied. The active organic layers consisted of a planar heterojunction between a layer of Meso-Tetrakis(4-BromoPhenyl) Zinc(II) Porphyrin (BrPhPZn) as electron donor (ED) and a layer fullerene molecules. The devices were fabricated in a high vacuum by thermal sublimation, a technique that allows multilayer devices realization easily by successive depositions, and it does not require solvents, achieving purer films with reproducible characteristics. Taking into account that the anodic contact, a key factor for cell efficiency, is favored by the inclusion of a thin anodic buffer layer (ABL), the effect on the yield after including one or two (ABL): MoO 3 or MoO 3 -CuI layers was studied. The cell which has the best photovoltaic characteristics has a BrPhPZn (ED) thickness of only 12.5 nm. This small thickness is related with the low conductivity of this organic molecule. On the other hand, including a thin MoO 3 -CuI bilayer increased, such device's efficiency in a 200%, with regard to a cell without ABL, getting for one cell ITO/MoO 3 -CuI/BrPhPZn/C 60 /Alq 3 /Al, with a 1.03% yield.

Small molecules organic photovoltaic devices based on the planar heterojunction porphyrin derivates/fullerene

“…Therefore, the high Rsh achieved with MoO 3 and better conductivity obtained with CuI explains the highest efficiency of the double anode buffer layer (DABL) MoO 3 /CuI. About the different morphologies of the organic film, it should be noted that the surface energy of the anode covered with MoO 3 is strongly higher than that of the anode covered with CuI [15,16], which explains that the growth of the organic film is different. Moreover it is known that CuI exhibits a high reactivity with the sulphur, nitrogen of the organic molecules [18][19][20][21][22].…”

“…The ABL, CuPc, C60, BCP and aluminum layers were deposited sequentially onto the substrate by sublimation or evaporation. Following an earlier study, we chose to work with a CuI layer thick of 1.5 nm and the deposition rate of CuI being 0.005 A°/s [16]. According to results previously obtained, the thickness of the MoO 3 layer was 4 nm, that of C60 was 40 nm and that of Alq 3 nm 8 nm [17].…”