通过旋涂在单晶硅晶片上形成发射极层

1. Introduction

During last decades, the researcher mainly focused on cell  efficiency improvement and watt peak cost reduction for  crystalline silicon solar cells. Most of PV industries use the  standard fabrication process for the reduction of the process  cost. The emitter is the most important part and the  formation of emitter constitutes a crucial step in the  manufacturing of the crystalline silicon solar cells. In case of  crystalline silicon solar cell processing, carrier diffusion into  p-type or n-type wafer creates emitter formation. For emitter  formation the most used technique in photovoltaic industry is  POCl3 diffusion in cylindrical quartz tube. Spin-on dopants  (SOD) also provide an impurity source for semiconductor  junction as well as emitter layer fabrication.

In this work, our goal is to put an intermediate step in  between lab-scale fabrication and fully automated  commercial facilities or processes. That’s why, the principal  motivation is to put stress on the simplicity and the cost  effective fabrication process. The use of low cost commercial CZ wafers and the use of SOD instead of doping  gas POCl3 can made this work interesting for a low budgeted  and industrially compatible fabrication process of solar cells.  Eventually, smaller fabrication facilities may be benefited  from these comparative studies and get involved in more  human resource involved manufacturing around the world  to make this technology reachable to all with reduced  production cost.

2. Related Works

Lachiq et al. reported a fabrication scheme where the  authors used a spin on dopant solution to obtain diffusion  with a rapid thermal annealing process in an inert  atmosphere. The authors retained the thin (<20 nm) SOD  film to serve as a surface passivation layer with further need  for an ARC [4].

Vikram et al. at University of Virginia in 2010  demonstrated a simplified and single step process on P-type  CZ–Si and FZ–Si wafer for photovoltaic device fabrication.  Single step process incorporates doping, anti-reflection  coating (ARC) and a surface passivation layer. P5O9 was  served as the dopant solution for photovoltaic device  fabrication [5].

Fig1

Edge Isolation The Phosphorus doped layer covers the entire surface  including edges. It is important to disconnect the front emitter from the back contact through etching the edges of  the sample. Several processes are involved such as chemical etching, plasma etching, laser cutting, mechanical sawing,  grinding with sand paper, single side etching etc. In this  research single side etching and laser cutting techniques  were used. For the single side etching, HF/HNO3 acid  barrier paste was used. It was carried out by screen printing  process. Samples were heated by 120°C for 10 minutes by  oven. Advantages of single side etching are preserving the  active cell area, lower parasitic loss, higher FF compared to  laser isolation process [3].

The four point probe apparatus is one of the standard  apparatus for the measurement of resistivity of  semiconductors. If the sample is in the form of a thin wafer  or the form of a thin semiconductor material deposited on a  substrate then it is also useful for the measurement.