Inverted polymer solar cells fabricated by a pre-metered coating process

Abstract

We herein report on the photovoltaic (PV) effect of inverted polymer solar cells (PSCs) that consist of a bulk-heterojunction (BHJ) PV layer and a sol–gel-derived zinc oxide (ZnO) electron-selective layer, produced by a simple pre-metered horizontal-dipping (H-dipping) process. For the BHJ PV layers that consisted of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) (P3HT:PCBM) with an indium-tin-oxide (ITO) cathode and an Ag anode, it was shown that the use of the H-dipping process in the fabrication of inverted PSCs resulted in a reliable and reproducible device performance; furthermore, an inverted P3HT:PCBM PSC fabricated by H-dip-coating had a power conversion efficiency (PCE) of 2.93%, which within the deviations seen was slightly higher than that of a reference device (2.75%) fabricated by conventional spin-coating. This device performance may be attributed to the homogeneous formation of functional ZnO and PV layers on the ITO cathode. Moreover, the H-dipping process was also applied to fabricate PV cells on a large-area substrate (50 × 50 mm²), which also showed that the fabrication of large-area inverted PSCs is relatively straightforward. The use of this pre-metered coating process in the fabrication of ZnO layers could be of considerable benefit in the future development of all-solution- and/or large-area inverted PSCs.