Cu ₂ (Zn _x Sn _2‐x )(S _y Se _1‐y ) ₄ Monograin Materials for Photovoltaics

Abstract

In monogram solar cells powders replace wafers or thin films. This allows for cheaper and much more efficient materials production and minimize materials loss. The separation of materials formation from the module fabrication -allowing for all temperatures and purity precautions-is the very important advantage of the monograin layer based technology. Large area module fabrication proceeds without any high temperature steps in a continuous roll-to-roll process. No up-scaling problems arise as is typical of thin-film technologies since a homogenous powder leads to homogenous modules. The influence of different technological parameters to the materials properties was studied and from CZTS=Cu2(Zn x Sn2. x )(S y Sei_ y ) 4 ) monograin powders solar cells have produced with parameters V oc up to 690 mV, fill factors up to 65 % and I sc more than 20 mA/cm . It was founded that changing of the sulfur/selenium ratio allows a change of 1.04 and 1.72 eV the band gap of Cu2(Zn x Sn2-x )(S y Sei. y )4. INTRODUCTIONClimate change and insecurity of power supplies are among the greatest problems for humankind at the moment and solutions are to be found within only a few decades. Large-scale introduction of renewable power systems in combination with a strong increase of power efficiency and saving will be the only way out. For example, in order to stabilize the world's climate a continuous growth of PV by at least about 20 % per year will be needed during the coming decades that will lead to PV installation of at least ten TW P before 2050. To realize these plans new abundant materials and cheap technologies are needed [1],The technologies used today for manufacturing solar cells are the wafer and the thin film technologies [2]. The wafer technology is based on the growth and use of very large monocrystals or the casting of ultrapure silicon or A3B5 materials. This is a very expensive process not only in terms of money but also in terms of energy input. Later these large single or polycrystals with a high degree of chemical purity and physical perfection have to be sawn into wafers which are subjected to sophisticated methods of oxidation, diffusion and chemical treatment in order to form localized regions of different types of conductivity needed for highly efficient solar cell structures. The idea of making crystalline solar cells by growing very large crystals and then cutting them into thin wafers is in fact not the most intelligent way to obtain perfect materials and structures. Thin film technologies of solar cells production can be applied, but the technical parameters of thin film solar cells are as a rule much worse than those of crystalline solar cells. On the other hand, thin film technologies are, in general, much cheaper than monocrystalline materials based technologies, both with respect to financial expenses and energy costs.Although silicon as semiconductor material is still dominating even in the thin film solar cell production, photovoltaic cells based on more complex compound semiconductor materials are becomi...