Zinc Oxide Modified with Benzylphosphonic Acids as Transparent Electrodes in Regular and Inverted Organic Solar Cell Structures

TL;DR

This study demonstrates a method to modify zinc oxide electrodes with benzylphosphonic acids, enabling their use in organic solar cells with performance comparable or superior to traditional ITO-based electrodes, challenging existing assumptions.

Contribution

It introduces a novel surface modification technique for ZnO to tune its work function over a wide range, facilitating its application in both regular and inverted organic solar cells.

Findings

ZnO work function can be tuned over 2.3 eV using phosphonic acid monolayers.

Modified ZnO electrodes perform on par or better than ITO/PEDOT:PSS in solar cells.

Inverted solar cells with modified ZnO do not require electron-blocking layers for high performance.

Abstract

An approach is presented to modify the WF of solution-processed sol-gel derived ZnOover an exceptionally wide range of more than 2.3 eV. This approach relies on the formation of dense and homogeneous self-assembled monolayers based on phosphonic acids with different dipole moments. This allows us to apply ZnO as charge selective bottom electrodes in either regular or inverted solar cell structures, using P3HT:PCBM as the active layer. These devices compete with or even exceed the performance of the reference cell on ITO/PEDOT:PSS. Our finding challenges the current view that bottom electrodes in inverted solar cells need to be electron-blocking for good device performance.