Thin‐film (25.5 μm) solar cells from layer transfer using porous silicon with 32.7 mA/cm2 short‐circuit current density

We fabricate a 25.5‐μm‐thick monocrystalline Si solar cell with a confirmed power conversion efficiency of 15.4% and an area of 3.88 cm² using a layer transfer process with porous Si. The process is free of photolithography and contains no high‐temperature oxidation steps. We investigate three design features that improve the short‐circuit current density to a value of 32.7 mA/cm² under AM1.5 illumination. The detached back reflector contributes 2 mA/cm², a reduced front‐surface reflectance accounts for an additional 2 mA/cm² and a reduced base doping increases the current density by 1 mA/cm². Copyright © 2002 John Wiley & Sons, Ltd.     

Sauer katalysierter Disulfidaustausch von S-Alkylthio-cystein-Derivaten

Proton-Catalyzed Disulfide Exchange of S-Alkylthio Cysteine Derivatives Although N-unprotected S-alkylthio cysteine derivatives are relatively stable in acid solutions, N-acylsubstituted and N-urethane protected S-alkylthio cysteines react easily by disulfide exchange. As a rule the frequently used tert.-butyloxycarbonyl amino protecting group, present in ethylthio cysteine derivatives can′t be removed selectively without disulfide cleavage, whilst the 2-(p-biphenylyl)isopropyloxycarbonyl and the 2-phenyl-isopropyloxycarbonyl amino protecting groups are removable without any structure change of the alkylthio thiol protecting groups. It is advisable to realize this acid demasking of the amino groups by means of weak deblocking reagents. Comperative experiments in acid solution prove S-tert.-butylthio group to be the most stable protecting function, whilst isopropylthio cysteine derivatives are more stable than the corresponding S-ethylthio compounds. All these results and experiments with addition of different thiols as well as u.v.-spectroscopic investigations indicate, that the observed acid catalyzed disulfide exchange proceeds via a carbonyl neighbouring group effect and formation of thiazolidinium and thiazolinium intermediates, respectively.