Syeda Husain

Improved p-n heterojunction solar cells employing thin film organic semiconductors

Abstract Scanning of organic dye pairs suitable for the fabrication of p-n heterojunction solar cells has led to the fabrication of new structures with improved response. The choice of dyes as well as the proper hierarchy among the materials in the cells was suggested by the electronic and optical dye characteristics so that more of the excitons generated by the absorbed quanta were delivered at the dye-dye interface. The cells were fabricated by vacuum evaporation of thin (200–400 A) dye layers on tin oxide covered glass. Both old and newly synthesized organic semiconductors were used. The major drawback of the one-dye cells used in the past is the limitation on the portion of the solar spectrum covered by the dye absorption spectrum. In the p-n heterojunction cells studied here this limitation has been successfully overcome and full visible solar spectrum coverage has been achieved. Internal current generation quantum efficiencies of the order of 7% have been demonstrated. Overall solar cell efficiencies of these structures, which are not thickness optimized, are still in the area of 0.1%. This is twice as high as the values previously reported for some p-n junction solar cells with organic semiconductors that did not take dye hierarchy and loss of energy through internal molecular transitions into account.

An approach to the optimal design of p-n heterojunction solar cells using thin film organic semiconductors☆

In recent work with p-n heterojunction solar cells constructed with pairs of photoconductive organic dyes, we have obtained short-circuit current yields of over 19%. The best results to date have been obtained with the pair chloroaluminum phthalocyanine (ClAlPc) and the bis-methylimide of perylenetetracarboxylic acid (DMP). The preferred configuration is SnO2/DMP/ClAlPc/Ag. This configuration has the advantage of placing the shorter wavelength absorber DMP against the transparent SnO2 input surface and facilitating Forster radiationless energy transfer from the DMP phase to the region of the active DMP/ClAlPc junction. It also makes best use of the electron-accepting and electron-donating properties of the two dyes. Through tests of single-dye Schottky cells with a variety of metal electrodes, we have learned that the Fermi levels of these two dyes lie too close together for optimum cell performance. Synthetic variants of the simple perylene dye and of ClAlPc have been prepared for stronger electron-accepting and electron-donating properties respectively.

Shaping the absorption and fluorescence bands of a class of efficient, photoactive chromophores: synthesis and properties of some new 3H-xanthen-3-

Abstract An approach to the systematic design of absorption and fluorescence band shapes is developed from considerations of the solvatochromism and electronic perturbation of unsymmetrical chromophores. The predicted spectral shifting and line broadening has been demonstrated within a series of newly synthesized substituted 6-amino-3H-xanlhen-3-ones 1 . A new method of presenting bandwidth data is developed which utilizes dipole strength-weighted moments of absorption bands.

Synthesis of photoaffinity labeling derivatives of d-glucose and d-galactose

Abstract Two new photoaffinity reagents having photoreactive groups attached to C-6 of d -galactose have been prepared. 6- N -(4-Azido-2-hydroxybenzoyl)- d -glucopyranosylamine and 6- N -(4-azido-2-hydroxybenzoyl)- d -galactopyranosylamine were synthesized by acylation of the protected amino sugars with 4-azidosalicoyl chloride or by treating the amine with 4-azidosalicylic acid. Subsequent iodination of the aromatic ring yields the diiodo derivative. Deprotection yields the sugar derivatized at C-6 by the diiodinated photoaffinity reagent. Photoaffinity reagents having high specific activity may be prepared by this procedure.