# Impact of the TCO Microstructure on the Electronic Properties of Carbazole-Based Self-Assembled Monolayers

## TL;DR

This paper shows how the structure of a transparent conductive oxide affects the performance of carbazole-based coatings in solar cells.

## Contribution

The study reveals how TCO microstructure influences work function shifts in hole-selective layers of solar cells.

## Key findings

- TCO microstructure directly affects work function shifts after SAM anchoring.
- Amorphous oxides lead to uniform surface potential distribution.
- Grain orientation in polycrystalline ITO correlates with local potential distribution.

## Abstract

Carbazole-based self-assembled monolayers (PACz-SAMs),
anchored
via their phosphonic acid group on a transparent conductive oxide
(TCO), have demonstrated excellent performance as hole-selective layers
in perovskite/silicon tandem solar cells. Yet, whereas different
PACz-SAMs have been explored, the role of the TCO, and specifically
its microstructure, on the hole transport properties of the TCO/PACz-SAMs
stack has been largely overlooked. Here, we demonstrate that the TCO
microstructure directly impacts the work function (WF) shift after
SAM anchoring and is responsible for WF variations at the micro/nanoscale.
Specifically, we studied Sn-doped In2O3 (ITO)
substrates with amorphous and polycrystalline (featuring either nanoscale-
or microscale-sized grains) microstructures before and after 2PACz-SAMs
and NiOx/2PACz-SAMs anchoring. With this,
we established a direct correlation between the ITO crystal grain
orientation and 2PACz-SAMs local potential distribution, i.e., the
WF. Importantly, these variations vanish for amorphous oxides (either
in the form of amorphous ITO or when adding an amorphous NiOx buffer layer), where a homogeneous surface potential
distribution is found. These findings highlight the importance of
TCO microstructure tuning, to enable both high mobility and broadband
transparent electrodes while ensuring uniform WF distribution upon
application of hole transport SAMs, both critical for enhanced device
performance.