Efficient inverted perovskite solar cells with a low-temperature processed NiO_x/SAM hole transport layer

Nowadays, the inverted (p-i-n) perovskite solar cells have gained increasing attention, especially with the emergence of self-assembled molecules (SAMs) such as MeO-2PACz, 2PACz, CbzPh, etc. The SAMs feature a simple preparation process and manifold substrate compatibility, and the electrical characteristics of the attached surface can be well regulated, which is of great significance for improving the device performance. Although there have been many studies about SAMs, some problems still exist. For example, there is a common problem of discontinuities (pinholes) in SAM, which can lead to severe interface recombination. Many SAMs have been proven to be p-type semiconductor materials that can be used as hole transport layers (HTLs). However, it is not yet known whether such a thin molecular film can effectively extract holes and block electrons, as both electrons and holes may tunnel through it. Here, we investigate the roles of MeO-2PACz in improving device performance. Afterwards, a thin NiOx layer prepared at low temperature (120 degrees C) is introduced to improve the coverage of the MeO-2PACz SAM layer to further optimize the energy level alignment and passivate defects at the perovskite bottom interface. As a result, the power conversion efficiency (PCE) of the champion device approaches similar to 22% with a high fill factor (FF) of 83.9%. Furthermore, the ITO/NiOx/SAM device can maintain 82% of its initial PCE after storing in the ambient air at 25 degrees C with RH of 20-30% for 800 h.