Stable Organic-Inorganic Perovskite Solar Cells without Hole-Conductor Layer Achieved via Cell Structure Design and Contact Engineering

Within the past few years, the record efficiency of inorganic-organic perovskite solar cell (PSC) has improved rapidly up to over 20%. However, the viability of commercialization of the PSC technology has been seriously questioned due to the moisture-and thermal-induced instabilities. Here, it is demonstrated that these issues may be mitigated via cell structure design and contact engineering. By employing the hole-conductor layer-free cell structure and a bi-layer back contact consisting of a carbon/CH3NH3I composite layer and a compact hydrophobic carbon layer, the PSCs have shown excellent stability, inhibiting moisture ingression and heat-induced perovskite degradation. It is found that, the unique bi-layer contact enables the optimization of perovskite absorbers during thermal stress. As a result, instead of degradation, the devices present enhanced performance under heating at 100 degrees C for 30 min. The best-performing cell shows a final efficiency of 13.6% from an initial efficiency of 11.3% after thermal stress. Upon encapsulation, these cells can even retain 90% of the initial efficiencies after water exposure and over 100% initial efficiency under thermal stress at 150 degrees C for half an hour. This approach provides a facile way for stabilizing the PSCs and opens a door for viable commercialization of the emerging PSC technology.