# Enhancing the Open-Circuit Voltage of Perovskite Solar Cells by up to 120 mV using {\pi}-Extended Phosphoniumfluorene Electrolytes as Hole Blocking Layers

## TL;DR

This paper introduces { extpi}-extended phosphoniumfluorene electrolytes as hole-blocking layers in perovskite solar cells, achieving up to 120 mV increase in open-circuit voltage by improving interface properties and reducing recombination.

## Contribution

The study demonstrates a novel application of { extpi}-extended phosphoniumfluorene electrolytes as effective hole-blocking layers, enhancing device voltage and interface engineering in perovskite solar cells.

## Key findings

- Open-circuit voltage increased by up to 120 mV.
- { extpi}-PFEs effectively block holes and reduce recombination.
- Enhanced built-in potential confirmed experimentally and via simulation.

## Abstract

Four {\pi}-extended phosphoniumfluorene electrolytes ({\pi}-PFEs) are introduced as hole-blocking layers (HBL) in inverted architecture planar perovskite solar cells (PVSCs) with the structure of ITO/PEDOT:PSS/MAPbI3/PCBM/HBL/Ag. The deep-lying highest occupied molecular orbital (HOMO) energy level of the {\pi}-PFEs effectively blocks holes, decreasing contact recombination. We demonstrate that the incorporation of {\pi}-PFEs introduces a dipole moment at the PCBM/Ag interface, resulting in a significant enhancement of the built-in potential of the device. This enhancement results in an increase in the open-circuit voltage of the device by up to 120 mV, when compared to the commonly used bathocuproine HBL. The results are confirmed both experimentally and by numerical simulation. Our work demonstrates that interfacial engineering of the transport layer/contact interface by small molecule electrolytes is a promising route to suppress non-radiative recombination in perovskite devices and compensate for a non-ideal energetic alignment at the hole-transport layer/perovskite interface.

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Source: https://tomesphere.com/paper/1906.05899