Monolithically series-connected crystalline Si wafer cells for portable electronic devices

A simple process sequence for the fabrication of solar mini-modules from crystalline Si wafers for portable electronic devices, e.g. wrist watches, is presented. We apply a process, that we originally developed for modules from thin-film crystalline Si, to Si wafers for the first time. Its main features are the single-side-single-step (4S)-metallization and a busbar-only contacting scheme. First prototypes consisting of six series-connected cells show efficiencies up to 11% and an open circuit voltage of 3.624 V when measured under one sun AM1.5G-illumination. Fill factor and short circuit current density are 77% and 23.6 mA/cm/sup 2/, respectively. A multitude of mini-modules is processed on a single wafer in parallel.