Improving perovskite/carbon interfacial contact in carbon based perovskite solar cells by changing two-step spin coating sequence

Hole-transport-material free and carbon based perovskite solar cells (PSCs) are promising low-cost and highly-efficient solar cells. It has been reported in literature that incorporation of carbon black (CB) nanoparticles in carbon layer improved perovskite/carbon interfacial contact and, as a result, increased power conversion efficiency (η). In the present work, an alternative route was proposed and it was evaluated. In conventional fabrication route, carbon paste is coated on two-step deposited perovskite layer, but in proposed alternative route, carbon paste is first deposited on PbI2 layer and then CH3NH3I solution is infiltrated through it to convert PbI2 to perovskite. PSCs fabricated by conventional and alternative routes, using a carbon paste which didn't contain CB nanoparticles, showed average η of 4.3% ± 1.0% and 7.7% ± 1.6%, respectively. It was demonstrated that improvement of perovskite/carbon interfacial contact, due to protrusion of perovskite crystallites between graphite flakes, was the main reason of this efficiency enhancement. PSCs fabricated by conventional route and by using carbon paste, which contained CB nanoparticles, showed η of 5.9% ± 1.3%.