Octylammonium Iodide Induced In‐situ Healing at “perovskite/Carbon” Interface to Achieve 85% RH‐moisture Stable, Hole‐Conductor‐Free Perovskite Solar Cells with Power Conversion Efficiency >19

“Perovskite/carbon” interface is a bottle‐neck for hole‐conductor‐free, carbon‐electrode basing perovskite solar cells due to the energy mismatch and concentrated defects. In this article, in‐situ healing strategy is proposed by doping octylammonium iodide into carbon paste that used to prepare carbon‐electrode on perovskite layer. This strategy is found to strengthen interfacial contact and reduce interfacial defects on one hand, and slightly elevate the work function of the carbon‐electrode on other hand. Due to this effect, charge extraction is accelerated, while recombination is obviously reduced. Accordingly, power conversion efficiency of the hole‐conductor‐free, planar perovskite solar cells is upgraded by ≈50%, or from 11.65 (± 1.59) % to 17.97 (± 0.32) % (AM1.5G, 100 mW cm−2). The optimized device shows efficiency of 19.42% and open‐circuit voltage of 1.11 V. Meanwhile, moisture‐stability is tested by keeping the unsealed devices in closed chamber with relative humidity of 85%. The “in‐situ healing” strategy helps to obtain T80 time of >450 h for the carbon‐electrode basing devices, which is four times of the reference ones. Thus, a kind of “internal encapsulation effect” has also been reached. The “in situ healing” strategy facilitates the fabrication of efficient and stable hole‐conductor‐free devices basing on carbon‐electrode. “Perovskite/carbon” interface remains as a bottleneck for carbon‐electrode basing perovskite solar cells, especially for hole‐conductor‐free devices. Here an “in‐situ healing” strategy is proposed by simply doping OAI in the carbon paste, which helps to effectively reduce defects and strengthen contact at the interface, and hence elevates the device efficiency from ≈13% to >19%, with 85% RH‐moisture stability in addition.