Photovoltaic effect of PLZT in a layered film structure and its application to ultraviolet sensing

Abstract

This paper reports on the formation of a new layered film stmcture and the highly improved photovoltaic output of the lead lanthanum zirconate titanate (PLZT) employed. The new structure design is described using a top transparent indium tin oxide (ITO) electrode. PLZT in the 4-pm thick film was formed by means of a molecular organic deposition (MOD) raw solution. While the photovoltaic current of the PLZT layered film structure was more than 10' times larger than that of bulk ceramic and single crystal structures, the photovoltaic effect per unit in the layered film structure was almost the same as that in bulk ceramics.There are several kinds of ferroelectric materials that exhibit photovoltaic effects under near-ultraviolet illumination'. The most outstanding advantage of the photovoltaic effect is its high output voltage over kV. This phenomenon of ferroelectrics is entirely different from that of the semiconductor p-n junction. This is because the photovoltaic effect occurs within the material and is considered to be an optical property of the material itself. Photovoltaic effect holds promise in the following areas; 1) high electrical output voltage over kV, 2) transducer from optical energy to electrical one, 3) wireless energy transfer and 4) sensing system for ultraviolet light. These characteristics are useful and applicable to micro-electro-mechanical systems (MEMS). PLZT has been only used in bulk condition, a layered PLZT film structure was prepared using a repeated film coating process in this report.. The thickness of film was 4 mm. The lower gray part of the PLZT film is SiO2. The SEM inspection confirmed that the film structure was homogeneous. The interface between the lower electrode and the PLZT was flat and smooth without voids or deficiencies. Figure 2 is an XRD profile of the PLZT film. The presence of a typical perovskite structure was confirmed. We note that e had almost the same value as bulk PLZT, so the insurance of the film is adequate for electrical properties. Figures 3(a) and @) show the photovoltaic voltage and current, respectively. Both the photovoltaic voltage and current had linear relationships with the illumination intensity. Photovoltaic voltage and current reached 0.8 V and 1.7 pA in the region of highest light intensity at 150 mW/cm'. Table 1 gives a comparison of PLZT in formed film and bulk condition'. The photovoltaic current of film per unit width was 2 orders higher than that of the bulk material. Since bulk PLZT exhibits high photovoltaic voltage over kV and small photovoltaic current around nA per cm' and mm of thickness, it is difficult, with few exceptions, to explore useful and practical applications. differences are due to the characteristics of a PLZT structure between bulk and film. Though Figure l(a) shows a SEM figure of surface and @) a crossed sectional figure of formed film. These References 1, B.I.Shunan and V.M.Fridkin, "The photovoltaic and photorefractive effects in noncentrosymmetric materials", Gordon and Breach Sci.

Arising applications of ferroelectric materials in photovoltaic devices

“…17,18 An unique characteristic of FE-PV devices is that the photocurrent direction can be switched by changing the spontaneous polarization direction of a FE material with the electric eld. To date, the photovoltaic effect has been studied in the lithium niobate (LiNbO 3 ) family, [19][20][21][22][23][24] barium titanate (BaTiO 3 or referred to as BTO), 20 lead zirconate titanate (Pb(ZrTi)O 3 or PZT) family, [25][26][27][28] and bismuth ferrite (BiFeO 3 or BFO) family. [29][30][31][32] Among the next generation photovoltaic technologies, the ferroelectric photovoltaic effect is completely different from the traditional p-n junction photovoltaic effect as shown in Fig.…”

Design of Ferroelectric Double Perovskite Oxides as Photovoltaic Materials

“…Moreover, previously used FE-PV materials, such as perovskites BaTiO 3 , PZT, and LiNbO 3 , have an energy band gap greater than 3 eV, limiting their ability to absorb visible light (ranging from 1.65 to 3.1 eV) region. Furthermore, they have less efficient and exceedingly weak conductivity, which limits their photovoltaic (PV) applications. − Therefore, to obtain a highly efficient FE-PV device, the band gap must be reduced without affecting the FE properties. For example, BiFeO 3 (BFO) has been extensively investigated for PV applications due to its relatively low band gap (2.6 eV) compared to other FE materials .…”