Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells

Team: Anthony Arrett, Wei Chen, William Elliott, Brian Modtland, and David Rincon

Advisor/Client: Dr. Vikram Dalal

Overview• Goal: to improve the stability and efficiency of a-Si:H solar cells through

annealing and graded Boron doping• Concept: PIN Solar cell deivce topology. Decrease defects (clusters)

through high annealing temps. High clusters = poor efficiency and stability• Functional Specs:

– Photoconductivity > 1*10-5 Ω-1 cm-1

– Dark Conductivity < 1*10-10 Ω-1 cm-1

– Tauc Band Gap < 1.8eV– Defect density after light soaking < 1*1016 cm-3

– Fill Factor > 60%– Efficiency > 5%– Drop in Efficiency after light soaking of no more than 10%

Background of a-Si:H

• What is a-Si:H (hydrogenated amorphous silicon)?

• Advantages of a-Si:H– Cheaper, Easy to Make– Large Area Cells

• Causes of instability in a-Si:H– Dangling Bonds created by Incident Light

• Stradins breakthrough– Less Stability over Time with High –Temp Anneal

Staebler-Wronski Effect

Our approach

• Annealing at high temperatures– Decrease dangling bond clusters

• Boron graded doping– Improve built-in field for carrier collection

• Trial and error using several different “recipes” for the production of a more stable a-Si:H device

Questions