# A lateral heterojunction device as a tool to study perovskite-based solar cells

Davide Regaldo, Pilar Lopez-Varo, Nitin Mallik, Javid Hajhemati, Vincent Dufoulon, Guillaume Vidon, Stefania Cacovich, J Alvarez, Jean Baptiste Puel, Philip Schulz, et al.

► To cite this version:

Davide Regaldo, Pilar Lopez-Varo, Nitin Mallik, Javid Hajhemati, Vincent Dufoulon, et al. A lateral heterojunction device as a tool to study perovskite-based solar cells. 40th European Photovoltaic Solar Energy Conference and Exhibition (EU-PVSEC), Sep 2023, Lisbon, Portugal. hal-04296790

HAL Id: hal-04296790

https://centralesupelec.hal.science/hal-04296790v1

Submitted on 29 Aug 2024

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Distributed under a Creative Commons Attribution 4.0 International License
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# A Lateral Heterojunction Device as a Tool to Study Perovskite-Based Solar Cells

## Scope of the work

Study the perovskite (PSK) properties on top of different substrates:

- Surface work function (WF);

- Defect and ion properties;

Previous knowledge:
Perovskite WF dependence on the substrate WF

<figure><img src="image_6.png" /></figure>

ACS Energy Lett. 2019, 4, 1–7
S. P. Dunfield et al., (2021).

<figure><img src="image_7.png" /><figcaption>Cross section view</figcaption></figure>

Previous device allowed to fix an upper limit of the doping density in the PSK layer:

$$N_{\text{dop}} \le 10^{12} \text{ cm}^{-3}$$

## XPS equilibrium characterization

The scan of the X-ray electron collection area (with 10 µm diameter) along the PSK surface, from the TiOₓ to the NiOₓ side revealed an iodine core level shift of 650 meV, in agreement with the WF difference between the TiOₓ and the NiOₓ surface.

<figure><img src="image_8.png" /></figure>

Drift-Diffusion model: band diagrams for intrinsic perovskite

<figure><img src="image_9.png" /><figcaption>Actual Potential</figcaption></figure>

Surface Potential as a function of PSK doping density

$$N_{\text{dop}} \le 10^{11} \text{ cm}^{-3}$$

<figure><img src="image_10.png" /><figcaption>Convolution with 10 µm spot size</figcaption></figure>

## LHJ structure and fabrication

3 photolithography steps to deposit:

- Contact layer: Ti (adhesion to glass) / Au (high conductivity) / ITO (PSK protection);

- Electron transport layer: TiOₓ;

- Hole transport layer: NiOₓ.

<figure><img src="image_11.png" /><figcaption>Cross section view</figcaption></figure>

<figure><img src="image_12.png" /></figure>

## KPFM substrate characterization

<table><caption>Work functions (KPFM)</caption><tr><td>ITO</td><td>4.95 eV</td></tr><tr><td>NiO<sub>x</sub></td><td>≥ 5.10 eV</td></tr><tr><td>TiO<sub>x</sub></td><td>≤ 4.50 eV</td></tr></table>

<figure><img src="image_13.png" /></figure>

$$\Delta_{\text{WF}} = WF_{\text{NiOx}} - WF_{\text{TiOx}} \ge 0.6 \text{ eV}$$

## XPS under Light and Voltage bias

<figure><img src="image_14.png" /><figcaption>Scan in the « dark »</figcaption></figure>

$\Delta I_{3d_{5/2}} = V_{bi}$
$= 0.7 \text{ V}$

$I_{3d_{5/2}}$ shift
$= \text{built in}$
voltage

<figure><img src="image_15.png" /><figcaption>Scan under illumination</figcaption></figure>

The applied voltage modifies $V_{bi}$:

$$\text{RV B: } V_{bi} - V_{app} = 0.7 + 1 = 1.7 \text{ V}$$

$$\text{FW B: } V_{bi} - V_{app} = 0.7 - 1 = -0.3 \text{ V}$$

No hysteresis in the dark 0 V scan, after applying light.

<figure><img src="image_16.png" /></figure>

The full dataset

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

## CONCLUSIONS

NiOₓ and TiOₓ - based LHJ device: various PSK channels created between the two contacts (lengths ranging from 10 to 100 µm). Double cation perovskite spin coated on the LHJ: the selective contacts under the PSK determine the potential drop in the PSK ($V_{bi}$) which can be modulated by an applied bias. PSK doping density measured $\le 10^{11} \text{ cm}^{-3}$.

Dunfield et al., **Carrier gradients and the role of charge selective contacts in lateral heterojunction all back contact perovskite solar cells**, Cell Reports Physical Science 2, 100520.
Regaldo, D et al, **On the equilibrium electrostatic potential and light-induced charge redistribution in halide perovskite structures.** Prog Photovolt Res Appl. 2022; 1-9.