# Normal and inverted hysteresis in perovskite solar cells

## TL;DR

This paper investigates the phenomena of normal and inverted hysteresis in perovskite solar cells, analyzing how pre-poling bias affects the hysteresis type and proposing a measurement protocol for accurate efficiency evaluation.

## Contribution

It demonstrates the dependence of hysteresis type on pre-poling bias and introduces a dynamic electrical model to explain the behavior, along with a standardized measurement protocol.

## Key findings

- Normal hysteresis occurs at positive pre-poling bias.
- Inverted hysteresis appears at negative pre-poling bias.
- A three-step measurement protocol improves PCE accuracy.

## Abstract

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO$_2$/CH$_3$NH$_3$PbI$_{3-x}$Cl$_x$/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, the behavior strictly depending on the pre-poling bias. NH typically appears at pre-poling biases larger than the open circuit bias, while pronounced IH occurs for negative bias pre-poling. The transition from NH to IH is marked by a intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model (DEM). Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the non-linear polarization. Introducing a three step measurement protocol, which includes stabilization, pre-poling and measurement, we put forward the difficulties and possible solutions for a correct PCE evaluation.