Performance Study Of Al-doped ZnO Films And Its Application In Flexible Solar Cells

ZnO belongs to Ⅱ-Ⅵ group semiconductor material with direct band gap, has excellentpiezoelectric, optical, pressure sensitive and other features. In recent years, ZnO doping hasachieved a lot of attention. Compared to ITO, Al doped ZnO (ZnO: Al) owns comparableoptical, electrical properties, and rich in raw materials, low cost, stable in physical andchemical circumstances. Moreover, ZnO: Al is stable in H plasma, and it is expected tosubstitute for ITO in solar cells.In the paper, radio frequency (RF) magnetron sputtering technologies are employed toin-situ deposit ZnO: Al on polyimide (PI) substrates. The influence of Ar flow and RF poweron films’ crystalline state, morphologies, electrical and optical properties have beensystematically studied. Thin-film crystal structures highly depend on Ar flow, and films havemost intense (002) preferred orientation at50sccm. As Ar flow increased, ZnO: Al films’optical band gap narrowing. As RF power increased, ZnO: Al films’ Hall mobility climbedslightly and films presented mixed orientation. It’s observed significant Burstein-Mossmoving phenomena and had a significant increase in the optical band gap. Eventually, thedepositing conditions were optimized. Ar flow and RF power are fixed at50sccm and125W,respectively. Films possess the best performance with the resistivity of2.62×10-3cm,visible light transmittance of85%, with a dense surface structure and grain size of50nm.ZnO: Al films properties greatly depend on substrate materials. In this paper, it’s studiedon the effect of substrates, including glass, PI and stainless steel (SS) on film properties,hoping to manufacture various ZnO: Al films suitable for different devices. Due to latticemismatch between ZnO: Al films and substrates, films produced plane stress and impairedtheir performance. Films on stainless steel owned maximum stress-2.77Mpa, which resultedin squeezing the lattice so that the lattice constant c is reduced to5.1945. ZnO: Al films onSS have inferior crystallographic and electrical properties, but the best surface morphologieswith similar inverted pyramid structures on the surface, which can be used as TCO electrodeand anti-reflection layer for solar cells.ZnO: Al films were introduced into flexible thin film solar cells as transparent electrodeand buffer layer. The cells were fabricated on PI and SS by plasma-enhanced chemical vapordeposition (PECVD) method. Compared with ITO based solar cells, cells with ZnO: Al have smaller circuit voltage (Vos) and short-circuit current (Isc), PI substrate and SS substrate basedcells’ open circuit voltage (Vos) and short-circuit current (Isc) were253mV,0.67mA/cm2and268mV,0.87mA/cm2.