Electrodeposition and characterisation of CdTe films for solar cell applications

• Published in: Electrochimica acta 2000-06, Vol.45 (20), p.3355-3365
• Main Authors: Duffy, N.W, Peter, L.M, Wang, R.L, Lane, D.W, Rogers, K.D
• Format: Article
• Language: English
• Subjects: Cadmium telluride; Electroabsorbance; Electrodeposition; Electroreflectance; Flow cell; Photocurrent; Solar cells; Sulfur diffusion
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/S0013-4686(00)00409-6

Thin film CdS/CdTe solar cells have been prepared by electrodeposition of CdTe on CdS coated conducting glass from an acidic electrolyte containing a high concentration of Cd 2+ and a low concentration of TeO 2. Deposition of a 2 μm CdTe film from stirred solutions typically requires 3 h. High quality CdTe films have been grown much more rapidly using a channel flow cell: 2 μm films were deposited in around 24 min. The CdTe|CdS thin film structures obtained in this way were characterised by photocurrent spectroscopy, electrolyte electroreflectance/absorbance spectroscopy (EER/A), XRD and AFM. CdS|CdTe films prepared by both methods were annealed at 415°C to effect type conversion of the CdTe layer. As deposited CdTe is generally n-type and exhibits strong preferential 〈111〉 orientation. Type conversion is not necessarily accompanied by recrystallisation: most of the CdTe films deposited from stirred solution did not recrystallise. Recrystallisation did occur for films grown by pulsing the potential periodically from 50 mV to>350 mV versus Cd 2+/Cd during deposition. Evidence for sulphur and tellurium diffusion leading to alloy formation during annealing was obtained from bandgap shifts detected by photocurrent spectroscopy and EER/A and from changes in lattice parameters measured by XRD. The composition of the annealed electrodeposited structures approached CdS 0.95Te 0.05|CdTe 0.95S 0.05 after 15 min. Test solar cells with AM 1.5 efficiencies approaching 6% were fabricated. Recrystallised samples gave higher solar cell efficiencies than non-recrystallised samples.