Wooyeon Kim1,Min Jae Ko1
Hanyang University1
Perovskite solar cells (PSCs) have emerged as promising next-generation photovoltaic devices because of their superior optical and electronic properties. In recent years, organic hole transporting material (HTM) based PSCs have been reported with remarkable increase in the photovoltaic performance. As power conversion efficiency (PCE) of PSCs employing organic HTM has dramatically increased, expectations toward commercialization of PSCs are increasing. However, traditional organic HTMs have a couple of issues such as cost and stability. In the view of this limitation, we have developed the new p-type inorganic HTM. Cobalt sulfide compounds are one of the promising materials to replace conventional organic HTMs, which are less expensive and earth-abundant. Nevertheless, synthesis of cobalt sulfide is tricky to control the stoichiometric ratio. Here, we synthesized novel inorganic HTMs as a stoichiometrically adjusted p-type cobalt sulfide nanocrystals (Co<sub>x</sub>S<sub>y</sub> NCs). Cobalt sulfide nanocrystals synthesized in this study display the excellent hole transport ability owing to its high conductivity and suitable energy levels for hole extraction for PSCs. Co<sub>x</sub>S<sub>y</sub> NCs HTLs-based PSCs exhibited power conversion efficiency (PCE) nearly comparable to dopants-free spiro-OMeTAD HTM-based PSCs. Especially, the PSCs with mixed Co<sub>x</sub>S<sub>y</sub> NCs (with undoped Spiro-OMeTAD) HTLs exhibited PCE of 20.48 % which belongs to the high-performance, considering ionic additive-free HTMs. Furthermore, the PCSs employing cobalt sulfide showed an initial efficiency of 92 % even after exposure to 70 % relative humidity for 1000 hours. These new p-type Co<sub>x</sub>S<sub>y</sub> NCs would support environmentally and economically sustainable development of PSC and diverse optoelectronic area.