Patterned masking using polymers: insights and developments from silicon photovoltaics

Abstract

Patterning is fundamental to advancing most technologies. Although the challenge for electronic integrated circuits continues to be reduced feature size other applications have different requirements and challenges. This review contributes insights from silicon photovoltaics where patterning is required for selective doping etching and metallisation. Earlier silicon solar cell devices extensively used optical lithography to fabricate devices in the laboratory with high device efficiencies being achieved. However industrial cell fabrication has largely relied on uniformly doped silicon layers and lower resolution screen-printing for metal electrode formation because optical lithography is considered too expensive and slow. This has resulted in the average energy conversion efficiencies of industrially produced cells remaining on average 5% lower than the value of 25% reported in 1999 for cells patterned with optical lithography. Motivated by the goal of bridging this efficiency gap many new polymer patterning methods which do not require the formation of a qualified mask have been developed for different silicon solar cell designs. These polymer patterning methods fall into two general classes; (i) where the polymer mask is directly printed on the cell surface; and (ii) where a pattern is formed in a polymer layer using printers or lasers to effect the patterning. Many of the methods which are reviewed in this paper although developed with specific photovoltaic requirements in mind may also find applications in other fields of research and technology.