Small-sized single crystalline silicon solar cells (ca. 25 mm(2)) were fabricated by a non-vacuum process as an energy supply for small devices (ubiquitous devices: a wristwatch, desktop calculator etc.) and processed for a tandem solar-cell research. A side-edge etching procedure was performed in order to eliminate detrimental cracks to improve photovoltaic properties. Moreover, the new structure of the small-sized solar cell with side contact provides reduced shadow loss of contacts. After the structural and procedural optimization, a conversion efficiency of 16.4% was achieved by a non-vacuum process with 3 mm x 8 mm surface dimension solar cell. Finally, the photovoltaic characteristics of small silicon cells, as a function of light intensity for the ubiquitous purposes were compared with amorphous silicon solar cells. In addition, the facile processed silicon solar cell was integrated into mechanically-stacked tandem solar cells with perovskite solar cells by direct contact of TCO layers of each sub-cell. The counter electrode MoOX/IZO over HTM (spiro-OMeTAD) in top perovskite cells is physically placed on top of the bottom Si solar cell to form a series tandem configuration. (C) 2017 Elsevier Ltd. All rights reserved.