Combinatorial solar cell libraries for the investigation of different metal back contacts for TiO2-Cu2O hetero-junction solar cells

Here we present a comprehensive investigation of TiO 2 -Cu 2 O hetero-junction solar cells with different back contacts (Au, ITO, Cu or Ag). Combinatorial hetero-junction libraries consisting of a linear TiO 2 thickness gradient produced by spray pyrolysis and a bell shaped Cu 2 O profile synthesized by pulsed laser deposition were chosen to investigate the impact of the two metal oxide layer thicknesses. The back contacts were deposited as round patches onto a grid of 13 × 13 points, 169 contacts for each contact material, forming a library containing 4 × 13 × 13 = 676 back contacts. Each back contact represented a solar cell with an individual TiO 2 and Cu 2 O thickness. I - V measurements show that all four materials provide an ohmic contact and that the open circuit voltage of ∼300 mV is rather independent of both layer thicknesses and contact material. The size of the Cu 2 O crystals drastically decreases with distance from the center of deposition, which leads to a drastic increase of series resistance when the crystal size is