Polymer interface engineering enabling high-performance perovskite solar cells with improved fill factors of over 82%

The solution-processed perovskite films inevitably induce defects, adversely affecting the device performance and environmental stability. Motivated by the small molecular passivation agents, a systematic work is carried out to reveal the role of P4VP polymer in perovskite solar cells. The introduction of P4VP polymer can reduce the defects at the surfaces and grain boundaries by coordinating with undercoordinated lead sites. The substantially reduced defect density leads to reduced non-radiative recombination, and extended electron diffusion length. Furthermore, a good match of energy levels at the perovskite/PCBM interface is achieved, which favors efficient electron extraction and suppresses the hole transfer. As a result, the power conversion efficiency increases from 17.46% to 20.02% after defect-passivation and improved energy level alignment with a significantly enhanced fill factor of 82.61% and improved open circuit voltage of 1.09. In addition, the non-encapsulated devices exhibit enhanced moisture stability (60 +/- 5% humidity) and thermal stability (85 degrees C) after P4VP incorporation.