Solution‐Processed High‐Quality Cu 2 O Thin Films as Hole Transport Layers for Pushing the Conversion Efficiency Limit of Cu 2 O/Si Heterojunction Solar Cells

Cuprous oxide (Cu 2 O) is a nontoxic and earth‐abundant semiconductor material, which is a promising candidate for low‐cost photovoltaic applications. Although Cu 2 O‐based solar cells have been studied for a few decades, they still suffer from disappointing photovoltaic performance due to its high trap‐state density and inferior carrier collection efficiency. Herein, a facile solution method is demonstrated to synthesize high‐quality Cu 2 O films with low defects as hole transport layers (HTLs) and the Cu 2 O/Si heterojunction solar cells are fabricated. Moreover, a variety of interfacial engineering and light management strategies are adopted to push the efficiency limit of Cu 2 O/Si solar cells, including a Ag transparent conductive layer, HNO 3 passivation, Mg electrode back contact, and MoO x antireflection layer, which enable the boosting of carrier separation and reduce the loss of incident solar light, yielding a record high power conversion efficiency of 9.54%. This work may pave the way for economical and environment‐friendly use of Cu 2 O/Si heterojunction solar cells in daily life.