Octylammonium Iodide Induced in-situ Healing Behavior at Perovskite / Carbon Interface: the "Slow-Release Effect" Caused by Carbon Black Adsorption.

"Perovskite / Carbon" interface has remained a key bottleneck for the hole-conductor-free perovskite solar cells based on carbon-electrode (CPSCs), due to problems like loose physics contact, defects, energy mismatch, poor chemical coupling, etc. A previous study shows that octylammonium iodide (OAI) blending in carbon paste induced a kind of "in-situ healing" effect for "perovskite / carbon" interface, and improved power conversion efficiency from ≈13% to >19%. Here the beneath mechanism is further explored by careful examination of the interaction between OAI molecule and carbon black (CB) nanoparticles. It comes to show that, the famous "CB adsorption" plays a key role during the "healing" processes. Due to CB adsorption behavior, the mass ratio between OAI and CB influences much on the healing effect. By suitably adjusting the mass ratio between OAI and CB, and increasing the light harvest of perovskite, an efficiency of 19.41% is achieved for the hole-conductor-free CPSCs. Device efficiency and the charge-extraction and recombination process are tracked with the storage period, continuous improvement appears for devices assembled by relatively higher CB mass. A kind of "slow-release effect" is revealed during the OAI-induced "in-situ healing" process, which is caused by the famous "CB adsorption" behavior.