Fully atomic layer deposited transparent carrier selective contacts for bifacial Cd-free Cu2ZnSnSe4 thin-film solar cells

Rosa Almache-Hernándeza; Gerard Masmitjà; Benjamín Pusay; Eloi Ros; Kunal J. Tiwari; Pedro Vidal-Fuentes; Victor Izquierdo-Roca; Edgardo Saucedo; Cristóbal Voz; Joaquim Puigdollers; Pablo Ortega

arXiv · 2507.15712

Fully atomic layer deposited transparent carrier selective contacts for bifacial Cd-free Cu2ZnSnSe4 thin-film solar cells

Rosa Almache-Hernándeza·Gerard Masmitjà·Benjamín Pusay·Eloi Ros·Kunal J. Tiwari·Pedro Vidal-Fuentes·Victor Izquierdo-Roca·Edgardo Saucedo·Cristóbal Voz·Joaquim Puigdollers·Pablo Ortega

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Abstract

Thin-film solar cells based on kesterite (Cu2ZnSnSe4) material are a promising alternative for photovoltaic devices due to their composition consisting of earth abundant elements, ease of production at a relatively low temperatures and excellent optical absorption properties. Additionally, this absorber compound allows a tuneable bandgap energy in the 1 to 1.5 eV window range, which makes it an attractive candidate either as a top or a bottom solar cell in tandem technologies combined with transparent carrier-selective contacts. However, conventional kesterite devices use a toxic CdS layer as an electron-selective contact, resulting in the difficultto-dispose chemical waste. This work explores the use of a stack of ZnO and Al-doped ZnO (AZO) films deposited by ALD to replace the CdS-based contacts in kesterite devices. The inclusion of a polyethylenimine (PEI) interlayer as dipole to enhance the overall electrical contact performance is also discussed. The transparent back contact is formed by an ALD V2Ox thin layer over a FTO conductive electrode. Fabricated kesterite solar cells exhibit remarkable photocurrent density values of 35 mAcm-2, open-circuit voltage around 260 mV and efficiencies up to 3.5% using front illumination. The aforementioned photovoltaic parameters yield to 5.3 mAcm-2, 160 mV and 0.3% respectively under back illumination, demonstrating the bifaciality of the proposed structure.

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Rosa Almache-Hernándeza, Gerard Masmitjà, Benjamín Pusay, Eloi Ros, Kunal J. Tiwari, Pedro Vidal-Fuentes, Victor Izquierdo-Roca, Edgardo Saucedo, Cristóbal Voz, Joaquim Puigdollers, Pablo Ortega. 2025-07-21. Fully atomic layer deposited transparent carrier selective contacts for bifacial Cd-free Cu2ZnSnSe4 thin-film solar cells. https://arxiv.org/abs/2507.15712

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