Stability of Efficient Ito-Free Inverted Organic Solar Cells

Abstract

The stability of encapsulated inverted organic P3HT:PCBM solar cells under illumination with 1000W/m2 by a sulphur plasma lamp (low UV-light intensity) at a temperature of 50°C in air is investigated. A thin layer of titanium or chromium as buffer layer on the aluminium electrode is used as electron contact. It turns out that devices with chromium as buffer layer are significantly more stable than devices with titanium as buffer layer. For 3% efficient devices with chromium as buffer layer, after a fast decrease on the first day, the efficiency recovers partially and stabilises at ca. 90% of the initial value). After this transient effect the efficiency decreases less than 10% during 1500h. Auger electron spectroscopy shows, that the metallic electron contact in the inverted solar cell is partially oxidised already for as prepared devices.