나노입자 기반 CIGS 태양전지의 흡수층 제조 및 광학특성

Abstract

CIGS, Cu(In1-xGax)(S1-ySey), is promising absorber materials for thin film solar cells due to high conversion efficiency, absorption coefficient and long-term stability. Especially, CIGS2, Cu(In1-xGax)S2 is a Se-free compound from the chalcopyrite family suitable for solar cells due to its high optical absorption and the direct band gap at 1.42~2.41 eV. In principle, solar cells based on sulfur chalcopyrites like CIGS2 have the same potential for high efficiencies as those based on selenium chalcopyrites. The development of CIGS2 is attractive, because the problematic selenium is substituted by the non-toxic sulfur. CIGS absorber layers are generally deposited by co-evaporation and sputtering method. These methods need a vacuum process that has significant drawbacks such as expensive cost, loss of resource materials and restriction of large-scale production. To solve these problems, non-vacuum processes have been suggested, which include electrodeposition, spraying and printing. Particularly, the printing method based on nanoparticle including screen printing and doctor-blade would be promising in terms of fast process, efficient use of the material and application of continuous roll-to-roll deposition. Among various synthesis methods of nanoparticle, ultrasonic spray pyrolysis(USP) is a powerful technique that has several advantages such as continuous operation, simple operation, high purity and excellent control of component ratio in mixed oxide systems. Especially, Salt assisted ultrasonic spray pyrolysis using the salt with precursor solution inhibits the agglomeration of nanocrystallites leading to the formation of non-agglomerated nanoparticles. In this study, CIGS2 absorber layer was synthesized using by non-vacuum process based paste coating and precursor powder used in paste coating was synthesized by salt assisted ultrasonic spray pyrolysis. CIGO and CIG alloy nanoparticle synthesized by salt assisted spray pyrolysis were deposited on Mo coated soda-lime glass and this were reduced and sulfurized to form CIGS absorber layer. CIGS2 phase was formed from all of the experiment. Especially, Grain growth and densification was observed from CIGS2 absorber layer synthesized from CIG ally nanoparticle.