Interface Formation in Cadmium-Free CZTSe Solar Cells: Influence of ALD Precursor Sequence and Nominal Subcycle Ratio

Description

This workbook contains eight worksheets with measurements from two champion CZTSe solar cells from the same absorber batch, one with a CdS electron transport layer and the other with a ZTO electron transport layer. For each device, the workbook includes illuminated and dark current density–voltage (J–V) curves, an external quantum efficiency (EQE) spectrum, and a reflectance spectrum. The first two rows of each worksheet identify the measured quantities and their units. J–V measurements were performed at 25 °C, scanning from reverse to forward bias. Illuminated curves were recorded under simulated AM1.5G illumination (100 mW cm⁻²). Current density was normalized to the total cell area of 0.087 cm². Photocurrent is reported as positive at short circuit. In all four J–V worksheets, the measured current density reaches a lower limit of approximately −120.7 mA cm⁻² at high forward bias.

Steps to reproduce

Absorber preparation. The two champion devices were fabricated using Cu2ZnSnSe4 (CZTSe) absorbers from the same batch. Cu/Sn/Cu/Zn metallic precursor stacks were deposited by sequential sputtering onto Mo-coated soda-lime glass and then selenized in sealed graphite boxes under a controlled Se and Sn atmosphere. Before electron transport layer deposition, the absorbers were immersed for 2 min at room temperature in a freshly prepared mixture of equal volumes of commercial 44% ammonium sulfide solution and deionized water, rinsed with deionized water, and dried under N₂ flow. Device fabrication. The zinc tin oxide (ZTO) electron transport layer was deposited by thermal atomic layer deposition at 120 °C using diethylzinc and tetrakis(dimethylamido)tin as the Zn and Sn precursors, and ultrapure H₂O as the oxidant. Each Zn-first supercycle comprised two ZnO subcycles followed by one SnOx subcycle. The sequence was repeated 233 times to obtain a nominal ZTO thickness of approximately 40 nm. The CdS reference layer was deposited by chemical bath deposition. Both devices were completed with approximately 50 nm of RF-sputtered i-ZnO and 200 nm of pulsed-DC-sputtered ITO. Both completed devices were heated on a hot plate in air at 235 °C for 25 min, without an additional ZTO-specific anneal. J–V measurements. Current density–voltage curves were recorded at 25 °C in the dark and under simulated AM1.5G illumination (100 mW cm⁻²), scanning from reverse to forward bias. The output of the Sun 3000 class AAA solar simulator (Abet Technologies) was checked before and after each measurement session using the same commercial Si reference cell with known photovoltaic parameters. Current density was calculated by dividing the measured current by the effective total geometrical cell area (0.087 cm²). Measurements were performed without an aperture mask, metallic contact grid, or antireflection coating. No spectral-mismatch correction was applied. EQE measurements. External quantum efficiency (EQE) spectra were acquired on the same two devices used for J–V characterization, using a Bentham PVE300 system calibrated with certified Si and Ge photodiodes. Reflectance measurements. Reflectance spectra were acquired using a PerkinElmer Lambda 950 UV–Vis–NIR spectrophotometer.

Institutions

• Institut de Recerca en Energia de Catalunya

  Catalonia, Barcelona
• Universitat Politècnica de Catalunya

  Catalonia, Barcelona

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