Pulsed Potential based E-ALD of PV Materials

A family of absorber materials of interest for high volume production of photovoltaics is referred to as CZTS, or Cu₂ZnSn(S,Se)₄.  The primary advantages of these materials are that they are made from nontoxic earth abundant elements.   This group has been working on E-ALD as a method for the formation of materials an atomic layer at a time for many years.  E-ALD provides atomic level control during the growth process and has been shown to form high quality deposits.  E-ALD is based on alternating precursor solutions of the desired elements and the use of UPD to limit growth to an atomic layer at a time.   The E-ALD method has important advantages for the formation of nanofilms of materials.   There are a broad range of new PV designs involving nanostructured electrodes and plasmonic layers where the thickness of an absorber layer can be much thinner than the µm needed for a typical thin film PV.   On such substrates, E-ALD should show important advantages for the formation of conformal nanofilms without annealing.  The main disadvantage to the use of E-ALD for the growth of PV, is the time it takes to grow a µm thick absorber layer.  The rate of growth is presently limited by the time it takes to change solutions.    Efforts by this group are being directed to the development of a variant of E-ALD based on potential changes, pulses, rather than solution exchanges.   This greatly increases the rate of deposition.   Presently, the Authors referred to it as potential pulse ALD (PP-ALD).   Preliminary results on the formation of Cu₂Se and other components of a CZTS buffer layer will be discussed.