Effect ofIn SituThermal Annealing on Structural, Optical, and Electrical Properties of CdS/CdTe Thin Film Solar Cells Fabricated by Pulsed Laser Deposition

Abstract

Anin situthermal annealing process (iTAP) has been introduced before the commonex situcadmium chloride (CdCl2) annealing to improve crystal quality and morphology of the CdTe thin films after pulsed laser deposition of CdS/CdTe heterostructures. A strong correlation between the two annealing processes was observed, leading to a profound effect on the performance of CdS/CdTe thin film solar cells. Atomic force microscopy and Raman spectroscopy show that the iTAP in the optimal processing window produces considerable CdTe grain growth and improves the CdTe crystallinity, which results in significantly improved optoelectronic properties and quantum efficiency of the CdS/CdTe solar cells. A power conversion efficiency of up to 7.0% has been obtained on thin film CdS/CdTe solar cells of absorber thickness as small as 0.75 μm processed with the optimal iTAP at 450°C for 10–20 min. This result illustrates the importance of controlling microstructures of CdTe thin films and iTAP provides a viable approach to achieve such a control.

Probing the Correlation of Twin Boundaries and Charge Transport of CdTe Solar Cells Using Electron Backscattering Diffraction and Conductive Atomic Force Microscopy

“…The details of the PLD procedure have been published elsewhere. 45,46 After the PLD growth, the CdTe/CdS samples underwent Cl treatment in a tube furnace under the Ar/O 2 atmosphere with ratios of 0:1−1:0 at 390− 410 °C for about 40−60 min. To conduct the Cl treatment, the CdCl 2 and methanol mixed solution was dip-coated onto a glass slide and placed on a heating stage until the methanol was completely vaporized.…”

“…TEC15 substrates from Pilkington Inc. were ultrasonicated for 10 min each in acetone and isopropyl alcohol, respectively, before being mounted into the PLD system for in situ growth of CdS and CdTe polycrystalline thin films. The details of the PLD procedure have been published elsewhere. , After the PLD growth, the CdTe/CdS samples underwent Cl treatment in a tube furnace under the Ar/O 2 atmosphere with ratios of 0:1–1:0 at 390–410 °C for about 40–60 min. To conduct the Cl treatment, the CdCl 2 and methanol mixed solution was dip-coated onto a glass slide and placed on a heating stage until the methanol was completely vaporized.…”