Semi-crystalline silicon photovoltaic cell - having large surface grains and junction extending into grains and along boundaries

摘要

The cell is formed in an Si wafer having a major surface adapted for impingement of light formed from randomly arranged, irregular, individual Si grains having mean dia. >=100 mu. (pref. >=1 mm) and grain boundaries that contact or are sepd. only slightly from adjacent grains at the impingement surface. A photovoltaic junction is formed extending across and below the surface and into the interior of the wafer along and inward of the grain boundaries, penetrating the wafer so that the total junction area exceeds the prod. of linear dimensions of the wafer surface but not so that the junction extends completely round the Si grain boundaries or to the opposite surface. The junction is formed by (a) diffusing impurity into the impingement surface and (b) maintaining in an atmos. free from the impurity at temp. and for a time causing the impurity to penetrate between grain boundaries and into individual grains. The cell gives satisfactory energy prodn., e.g. 15% conversion efficiency, at an efficiency/expense ratio much better than monocrystalline Si cells.