CHARACTERIZATION AND OPTIMIZATION OF LASER-DOPED SELECTIVE EMITTERS FOR APPLICATIONS IN SILICON SOLAR CELLS

Open Access
Author:
Woolridge, Jillian J
Graduate Program:
Engineering Science
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 01, 2011
Committee Members:
  • Dr Reutzel/Dr Ashok, Thesis Advisor
  • Edward William Reutzel, Thesis Advisor
  • S Ashok, Thesis Advisor
Keywords:
  • silicon solar cells
  • selective emitters
  • laser doping
Abstract:
Commercial or “standard” silicon solar cells (crystalline silicon cells with screen-printed front contacts, a PECVD silicon nitride layer, and an aluminum back-surface field rear contact) have reached a relatively stable plateau in terms of conversion efficiency. New methods of increasing efficiencies involve cell design modifications, with use of selective emitters being among the most popular. Selective emitters are highly–doped regions beneath front metal contacts which enhance collection, shield contacts from minority carriers, and lower device series resistance for an overall increase in device efficiency. Between the metal contacts, low doping is desirable to increase lifetime and blue-response. Laser processing with high-power, fast repetition rate lasers makes fast throughput and production adaptation feasible. By using lasers, selected areas or regions on cell surfaces can be heavily doped while maintaining light doping between these contact areas. In addition, lasers can produce these structures using a one-step process, in contrast to conventional techniques that require multiple steps such as deposition of masks, chemical etches, and high-temperature diffusion steps. Optical absorptivity in silicon is known to be a strong function of wavelength. UV is only absorbed within a few tens of nanometers, while near-IR wavelengths will travel a few hundred microns. Fluence and laser pulse duration define the peak irradiance, which is known to play a significant role in material interactions. This work investigates the influence of wavelength, fluence, and pulse duration on selective emitter performance to determine industrially feasible process conditions for producing selective emitter-based solar cells in a practical manner.