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In this work, the fabrication of MoOx-free semitransparent perovskite solar cells (PSC) with Power Conversion Efficiencies (PCE) up to 15.7% is reported. Firstly, opaque PSCs up to 19.7% were fabricated. Then, the rear metal contact was replaced by a highly transparent and conductive indium tin oxide (ITO) film, directly sputtered onto the hole selective layer, without any protective layer between Spiro-OMeTAD and rear ITO. To the best of our knowledge, this corresponds to the most efficient buffer layer-free semitransparent PSC ever reported. Using time-resolved photoluminescence (TRPL) technique on both sides of the semitransparent PSC, Spiro-OMeTAD/perovskite and perovskite/TiO2 interfaces were compared, confirming the great quality of Spiro-OMeTAD/perovskite interface, even after damage-less ITO sputtering, where degradation phenomena result less important than for perovskite/TiO2 one. Finally, a 4-terminal tandem was built combining semitransparent PSC with a commercially-available Aluminium Back Surface Field (Al-BSF) silicon wafer. That silicon wafer presents PCE = 19.52% (18.53% after being reduced to cell size), and 5.75% once filtered, to generate an overall 4 T tandem efficiency of 21.18% in combination with our champion large semitransparent PSC of 15.43%. It means an absolute increase of 1.66% over the original silicon wafer efficiency and a 2.65% over the cut Si cell.

Thin films of copper-indium-gallium mixed oxides/hydroxides are electrochemically deposited on molybdenum substrates in aqueous nitrate-based electrolyte in acidic conditions. The process is based on the local pH increase at the cathode surface due to the reduction of nitrate ions. A thermodynamical study shows that the electrochemically induced deposition of copper-indium-gallium mixed oxide/hydroxide films occurs at much higher potentials than their metallic counterparts. A voltammetric study presents the key role of Cu(II) reduction during the process to induce nitrate ions reduction, and shows that the deposition is then controlled by mass transfer of the Cu(II), In(III), Ga(III) species. The composition of the layer is remarkably precisely tuned in a large range of potential, which makes this process highly suitable for the synthesis of Cu(In,Ga)Se2 solar cells.

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