The conversion of greenhouse gas CO2 into novel materials is the most promising approach to solve greenhouse gas issues. Herein, we report for the first time the reaction of potassium with CO2 to synthesize three-dimensional honeycomb-like structured graphene (3DHG). Furthermore, 3DHG exhibited excellent performance as a counter electrode for hole transport material (HTM)-free perovskite solar cells, leading to a power conversion efficiency of 10.06%. This work constitutes a new aspect of potassium chemistry for material synthesis from a greenhouse gas and the generation of electrical energy from sunlight.Fil: Wei, Wei. Michigan Technological University; Estados UnidosFil: Hu, Baoyun. Tongji University; ChinaFil: Jin, Fangming. Shanghai Jiao Tong University; ChinaFil: Jing, Zhenzi. Tongji University; ChinaFil: Li, Yuexiang. Nanchang University; ChinaFil: Garcia Blanco, Andres Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada ; ArgentinaFil: Stacchiola, Dario Jose. Brookhaven National Laboratory; Estados UnidosFil: Hu, Yun Hang. Michigan Technological University; Estados Unido