Rebirth of CuInS2 as hole transport material for perovskite solar cells

Copper indium sulfide, CuInS2 (CIS), has entered the field of photovoltaic cells for about three decades but somehow, they have not met their theoretically predicted efficiency as an absorber material. However, it is being employed as a hole transport layer in conjunction with organic-inorganic perovskite solar cells, which offer improved environmental stability at a reduced production cost. This commentary piece aims to draw researchers' attention to the use of CIS as hole transport layers in organic-inorganic perovskite solar cells, with the expectation that further study and efficiency improvements will propel perovskite solar cells into the commercialization race.