Juras Ulbikas, Daiva Ulbikiene, Vida Janusoniene

Institute of Lithuanian Scientific Society, A. Gostauto 11-466, 01108, Lithuania Karolis Pozela

Semiconductor Physics Institute, A. Gostauto 11, 01108, Lithuania

To find methods for reduction of the PV Cells production costs per Watt while in the same time keeping optimized or even reaching higher performance of Solar Cells is the main challenge for PV Cells manufacturing technology. For the majority of commercially produced solar cells the dominant material up to now is still crystalline silicon (c-Si). A lot of efforts has been undertaken to increase the electrical efficiency of Si based solar cells, nevertheless commercially available products still have performance in the range 15-17%. One of the promising trends to achieve higher performance of the monocristaline Si based Solar Cells is development of complicated spatial structure on absorbing surface of PV Cell (so called Spatial Solar Cells). Reports indicate efficiencies as high as 24% in laboratory samples, but with significant raise in costs for Spatial SC production.

Increase in production costs is caused by introduction of additional costly processing steps and due to this, low possibility to use such improvements in commercial industrial products. Application of self-formation methods in Solar Cell technology (www. self-formation. lt) is expected to reduce technological processing steps leading to significant simplification of SSC processing. In our paper we will present recent experimental results of SSC development using Self-formation methods. First estimations demonstrate significant reduction of the production costs for SSC produced by Self-formation technology.

On the other hand with introduction of Spatial structure for Solar Cells, optimization of performance characteristics in dependence of developed spatial structure is becoming of primary importance. Simulation results on physical characteristics of SSC with different spatial structure will be presented as well. We expect that proposed method for optimization of SSC performance can become useful tool in the hands of technologists predicting and optimizing SSC properties.

Background

The use of conventional microtechnology patterning processes in Solar Cells manufacturing is one of the main obstacles for wide spreading of the commercial use of photovoltaic. Self-formation with its possibilities to reduce number of required patterning processes is one of the promising ways to reduce significantly SC production costs with parallel increase in SC efficiency. Self-formation as a concept for irreversible evolution of the artificial object with complexity increase was introduced for understanding of the processes existing in microelectronics technology [1]. Recently developed tools for simulation of technological processes for Solar Cells manufacturing [2] clearly indicate that self-formation is becoming interesting tool for technologists trying to create and optimize microelectronic devices.

Higher efficiency in monocristalline Si based Solar Cells typically is achieved by introduction of complicated spatial structure on absorbing surface of SC. Reports indicates efficiencies up to 24% in laboratory samples. This trend is still limited to laboratory stage due to significant production costs.

The mono-crystalline silicon solar cells with record performance characteristics requires 5-6 [3] patterning processes which are the high-priced manufacturing process part. In order to have cheaper product the number of patterning processes in mass manufacturing solar cells
are minimised to one or two, but cell efficiency falls to considerably smaller value. As it was shown in [4] the structure of PERL type solar cell can be realised by two photo-masks if self­formation elements are included into manufacturing process.

PERL solar cell [3] is realised by typical external formation which is normally used in planar technology. All needed patterns are brought from outside as photo-masks, which converts chaotic media (UV light) to structured one. Pattern in photo-mask is aligned with object pattern. All the other processes: development, etching and even doping, forms recurrent sequence after each patterning process and reproduces photo-mask pattern to the technological layers on the wafer or to the wafer.