When spiro-MeOTAD, a type of organic semiconductor, reacts with lithium-ion-encapsulating fullerenes, electron transfer occurs, and the radical cations of spiro-MeOTAD and neutral lithium-encapsulating fullerenes are generated. The former is a true hole transport carrier in the hole transport layer of perovskite solar cells. The latter removes oxygen that enters the solar cell devices and improves durability. This reaction mixture was dropped onto a perovskite solar cell having a single-walled carbon nanotube as an upper electrode to prepare a highly durable perovskite solar cell without a metal electrode. This solar cell showed a maximum power conversion efficiency of 17.2 and a stable time of 1100 hours under the conditions of temperature 60°C and humidity 70.
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