Katarzyna Znajdek

Investigation of ITO layers for application as transparent contacts in flexible photovoltaic cell structures

In this paper authors present the mechanical, optical and electrical parameters of Indium Tin Oxide (ITO) Transparent Conductive Layers (TCL) deposited on flexible substrate. Layers’ properties are analyzed and verified. Investigated Transparent Conductive Oxide (TCO) was deposited, using magnetron sputtering method. Flexible polymer PET (polyethylene terephthalate) foil was used as a substrate, in order to photovoltaic (PV) cell’s emitter contact application of investigated material. ITO-coated PET foils have been dynamically bent on numerous cylinders of various diameters according to the standard requirements. Resistance changes for each measured sample were measured and recorded during bending cycle. Thermal durability, as well as temperature influence on resistance and optical transmission are verified. Presented results were conducted to verify practical suitability and to evaluate possible applications of Indium Tin Oxide as a front contact in flexible photovoltaic cell structures.

Innovative Elastic Thin-Film Solar Cell Structures

The idea of thin films dates back to the inception of photovoltaics in the early sixties. It is an idea based on achieving truly low-cost photovoltaics appropriate for mass production, where usage of inexpensive active materials is essential. Since the photovoltaic (PV) modules deliver relatively little electric power in comparison with combustion-based energy sources, solar cells must be cheap to produce energy that can be competitive. Thin films are considered to be the answer to that low-cost requirement [1]. Replacement of single crystalline silicon with poly and amorphous films, caused the decline of material requirements, which has led to lower final prices [2]. Furthermore, the thickness of cell layers was reduced several times throughout the usage of materials with higher optical absorption coefficients. Unique, thin film and lightweight, devices of low manufacturing costs and high flexibility, were obtained by applying special materials and production techniques, e.g. CIS, CIGS or CdTe/CdS technologies and organic elements. Taking advantage of those properties, there is a great potential of new, useful applications, such as building integrated photovoltaics (BIPV), portable elastic systems or clothing and smart textiles as well [3]. Low material utilization, mass production and integrated module fabrication are basic advantages of thin film solar cells over their monocrystalline counterparts [4]. Figure 1 (by NREL) shows the development of thin film photovoltaic cells since 1975. The development of cadmium telluride (CdTe) based thin film solar cells started in 1972 with 6% efficient CdS/CdTe [5] to reach the present peak efficiency of 16.5% obtained by NREL researchers in 2002 [6]. Chalcopyrite based laboratory cells (CIS, CIGS) have recently achieved a record efficiency of 20% [7], which is the highest among thin film PV cells (see Table 1). Solar modules based on chalcopyrites, uniquely combines advantages of thin film technology with the efficiency and stability of conventional crystalline silicon cells [4].

Polymer substrates for flexible photovoltaic cells application in personal electronic system

The article presents an overview of polymeric materials for flexible substrates in photovoltaic (PV) structures that could be used as power supply in the personal electronic systems. Four types of polymers have been elected for testing. The first two are the most specialized and heat resistant polyimide films. The third material is transparent polyethylene terephthalate film from the group of polyesters which was proposed as a cheap and commercially available substrate for the technology of photovoltaic cells in a superstrate configuration. The last selected polymeric material is a polysiloxane, which meets the criteria of high elasticity, is temperature resistant and it is also characterized by relatively high transparency in the visible light range. For the most promising of these materials additional studies were performed in order to select those of them which represent the best optical, mechanical and temperature parameters according to their usage for flexible substrates in solar cells.

Printed PEDOT layers as transparent emitter electrodes for application in flexible inorganic photovoltaic structures

The purpose of the work is to find an appropriate flexible material to replace commonly used transparent conductive oxides (TCO) in photovoltaic (PV) emitter electrode applications. Authors show the alternative, potential possibility of using PEDOT conductive polymer as transparent emitter contacts for thin-film, flexible photovoltaic structures. The vast majority of contacts made of TCO layers, dominantly indium tin oxide ITO, are electrically unstable under the influence of mechanical stresses [1,2,3]. This drawback inhibits their usage in flexible devices, such as solar cells. The need of the development in the field of flexible PV structures induces searching for new materials. Investigated transparent conductive layers (TCL) were made of organic compositions based on PEDOT polymer and their parameters were compared with equally measured parameters of carbon nanotube (CNT) layers, commercial ITO and AgHT ultra-thin silver layers. Transparent conductive layers based on PEDOT:PSS compound were deposited on flexible substrates by screen printing technique. The analysis of achieved results shows the broad spectrum of application possibilities for PEDOT layers.

Experimental evaluation of ITO, AZO, TiO 2 and CNT compounds as transparent conductive layers for flexible PV structures

This paper presents a comparison of optical, electrical and mechanical properties of various types transparent conductive layers (TCLs). Metal oxides such as indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:Al) and titanium dioxide (TiO2), as well as carbon nanotube composites were utilized for layers manufacturing. For each TCL, different production technology was applied. All examined materials were deposited on flexible transparent polymer substrates. Obtained results were analyzed in order to verify suitability of investigated compounds for application in flexible photovoltaic structures as emitter electrodes. Presented paper is a part of the project of a new elastic PV cell construction.