# Modelling investigations of surface photovoltage including surface defects

James P. Connolly, Mattia da Lisca, Davide Regaldo, José Alvarez, Jean-Paul Kleider, Stefan Georgiev, Vesselin Donchev

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James P. Connolly, Mattia da Lisca, Davide Regaldo, José Alvarez, Jean-Paul Kleider, et al. Modelling investigations of surface photovoltage including surface defects. 12èmes Journées Nationales du Photovoltaïque (JNPV) 2022, Nov 2022, Dourdan, France. . [hal-03878613](https://hal.science/hal-03878613)

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Submitted on 25 Feb 2023

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<figure><img src="image_1.png" /></figure>

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# Modelling investigations of surface photovoltage including surface defects

J.P. Connolly¹, M. Da Lisca¹,², D. Regaldo¹,², J. Alvarez¹, J.-P. Kleider¹, S. Georgiev³, V. Donchev³

¹ Génie Electrique et Electronique de Paris (GeePs), UMR CNRS 8507, Université Pierre et Marie Curie, Université Paris-Saclay, CNRS, 11 rue Joliot Curie, Plateau de Moulon, Gif sur Yvette, France

² IPVF, Institut Photovoltaïque d'Ile-de-France, 30 route Départementale 128, F91120, France

³ Faculty of Physics, Sofia University "St. Kliment Ohridski", Sofia, Bulgaria

**KPFM principles** : see "Local probe microscopies for the study of III-V based solar cells", Mattia da Lisca et al., in this visual presentation session

**KPFM - issues** : Affinity, doping work function: BULK properties.
KPFM is **SURFACE technique**

**Solution** : Numerical modelling => KELSCAN modeling package (IPVF/GeePs)
Including geometry, surface defects, characterisation techniques

<figure><img src="image_2.png" /><figcaption>KELSCAN flow chart</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Back surface contacted AlGaAs multilayer</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Side contacted AlGaAs multilayer</figcaption></figure>

**Simulation methods** : (1) KPFM experiment mode : Simulation of the KPFM tip, numerical field minimisation point by point
(2) Field simulation mode : Numerical transport drift diffusion directly yields surface potential

**Simulation options** : Arbitrary illumination Field profiles on four surfaces - **KPFM** scanning on top section
Contacts on sides and / or back, kpfm tip on top section, option to remove contacts / tip

<figure><img src="image_5.png" /></figure>

**KPFM resolution** : KPFM tips of 10nm (red) and 100nm (blue)
**in the dark** and **(inset) zoom on the first peak.**

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

**Contact potential in the light** : In red field simulation mode, in blue KPFM simulation mode - both under illumination (dark not shown)

<figure><img src="image_7.png" /></figure>

**Surface photovoltage** : In red field simulation mode, in blue KPFM simulation mode -

**Evaluation of KPFM resolution** : **Weak dependence for two tip dimensions shown here** in the dark

**Simulation method** : Full KPFM simulation is noisy in the light and subject to an offset due to contact issues to be investigated

### pn junctions in the light with defective surfaces

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

Donor defects ND(peak) = 1e18/cm3/eV
Depletion mainly p-side (n-side doping gradient junction)

<figure><img src="image_9.png" /></figure>

Bands and populations for donor defects

<figure><img src="image_10.png" /></figure>

Light, dark KPFM scans, and SPV:
p-side QFL splitting due to the p-type surface defect layer.

Sample : c-Si : [p-1E17cm³ 0.27µm](n-1E17cm³ 0.27µm) - Defect layer 0.1µm thick - Illumination 0.5µm monochromatic, 1000W/m²

## Discussion:

* **Resolution** : Simulation decouples transport issues inherently limitins resolution from KPFM tip influences.

* **Simulation methods** : Simulation of experiment required to validate resolution. Direct solution far more efficient if possible.

* **Surface defects** : Modification of potential CPD profiles due to surface defects can be simulated
  Challenge : knowledge of surface defect properties.

* **In progress** : Modulated spectrally resolved SPV

To be detailed in a **follow-up JNPV publication in EPJPV**: Modification and explanation of CPD and SPV profiles due to defects