The Influence of the HOMO Energy Level of the Organic Electron Donor on the Effectiveness of the Anode Buffer Layer in Photovoltaic Solar Cells

Efficiency of organic photovoltaic cells, based on electron donor/electron acceptor junctions (ED/EA) could be strongly improved when the transparent conductive anode, is covered with a thin anode buffer layer (ABL) such as Au or MoO3. To study the influence of the HOMO (Highest Occupied Molecular Orbital) value of the organic material on the effectiveness of the anode buffer layer (ABL), different ED have been probed: pentacene, copper phthalocyanine (CuPc), tetraphenyldibenzoperiflanthene (DBP) and, poly(benzo[c]thiophene-2-oxide) with 5 eV, 5.2 eV, 5.5 eV and 5.52 eV as HOMO value respectively. The effects of a metal (Au) or an oxide (MoO3) ABL are reported. The results indicate that the improvement of the cells performance depends on the value of the ABL work function. A good matching between the work function of the anode and the highest occupied molecular orbital of the organic electron donor is the most important factor limiting the hole transfer efficiency. It is shown that the MoO3 oxide has a wider field of application as ABL than the Au metal.