Preparation of multi-functionalized ZnO colloids for electron transport layer of inverted polymer solar cells

Abstract

The multi-functionalized ZnO electron transport layer(ETL) was adapted in the inverted polymer solar cells(i-PSCs) to improve cell performances with replacing the previous complicate processes of organic-inorganic composite layer, like high temperature annealing or multi-layer coatings. The modification of 2-(2-methoxyethoxy) acetic acid(MEA) on the ZnO surfaces provided colloidal stability and prevented aggregation of particles in the case of poly-ethyleneimine(PEI) addition. The incorporated amount of PEI could be increased to ~10 wt% and the parameters of cell performance, such as Jsc and FF, were enhanced proportionally with PEI addition because of its contribution to work function decrease in ZnO ETL. Through the fabrication of i-PSCs with modified ZnO ETL, the power conversion efficiency(PCE) was increased by ~40% from 5.10 % to 7.16 %(maximum value: 7.50 %) in the structure of ITO/ETL/PV-D4610:PC60BM/ MoO3/Ag. Multi-functionalized ZnO colloids with MEA and PEI provide more facile process of organic-inorganic composite ETL in addition to the improved cell performances.