In order to improve hole collection at the interface anode/electron donor in organic photovoltaic cells, it is necessary to insert a hole‐transporting layer. CuI was shown to be a very efficient hole‐transporting layer. However, its tendency to be quite rough tends to induce leakage currents and it is necessary to use a very slow deposition rate for CuI to avoid such negative effect. Herein, we show that the co‐deposition of MoO3 and CuI avoids this difficulty and allows deposition of a homogeneous efficient hole‐collecting layer at an acceptable deposition rate. Via an XPS study, we show that blending MoO3:CuI improves the hole collection efficiency through an increase of the gap state density. This increase is due to the formation of Mo5+ following interaction between MoO3 and CuI. Not only does the co‐evaporation process allow for decreasing significantly the deposition time of the hole‐transporting layer, but also it increases the efficiency of the device based on the planar heterojunction, CuPc/C60.

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