KSEF R&D Excellence: Fabrication and Characterization of Solar Cells Based on Organic Semiconductors

Electrical & Computer Engineering Department, 453 Anderson Hall, University of Kentucky, Lexington KY 40506; Phone: 859-257-3243;Email: [email protected] Department of Chemistry, University of Kentucky, Lexington KY 40506; Phone: 859-257-8844; Fax (dept): 859323 1069; E mail: [email protected] Inorganic semiconductors like Silicon and Gallium Arsenide have been the backbone of the semiconductor industry for the last four decades. However, organic semiconductors like pentacene offer the advantages of low cost, large area processing and, compatibility with flexible and lightweight plastic substrates. They are emerging as revolutionary materials, which will transform the world of circuit and display technology. In particular, they hold great promise for low cost photovoltaic and other electronic devices. The project proposal entitled "Fabrication and Characterization of Solar Cells Based on Organic Semiconductors" involves (1) synthesis of novel pentacene derivatives and their electro-optic, materials characterization (2) fabrication of Solar cells using pentacene as a P-type absorber layer and (3) Junction analysis of the CdS-Pentacene solar cells. Crystals and thin films of high conductivity pentacene derivatives are already being fabricated in our laboratories. The fabrication process for pentacene based solar cells has been initiated and the first few films and solar cell devices show good promise. In our preliminary work, we have focused on heterojunction solar cell structures and have fabricated heterojunction devices. The heterojunction choice was based on the finding that solar cells using ZnO:AlJpentacene organic-inorganic hetero junction exhibit better performance than AlJpentacene Schottky diode solar cells because in heterojunction cells, the region of absorption of solar photon occurs in or near the high field junction region. However, for exploiting several theoretical and practical advantages, we have introduced a thin layer of CdS deposited by solution growth, between the conducting oxide (ITO) and pentacene. The pentacene layer was deposited by vacuum evaporation from a source of high conductivity functionalized pentacene made in our laboratory. Finally gold was evaporated as the top electrode. The first device exhibited photovoltaic characteristics including an open circuit voltage of 500 mY. New devices are now being made. Under the proposed research, we will perform optimization studies to improve the cell performance e.g. by varying the nature of the functionalized pentacene, and exploring different device designs.