Perovskite solar cells are being studied because of their high efficiencies, low cost and easy fabrication process. However, perovskite crystals are unstable and decompose into PbI₂ in ambient air, and durability is one of the important issues for the perovskite solar cells. It has been reported that the photovoltaic properties and stability could be improved by adding polymers on the perovskite layer. In the present work, CH₃NH₃PbI₃ perovskite photovoltaic devices treated with a polysilane layer were fabricated and characterized. A decaphenylcyclopentasilane (DPPS) in chlorobenzene solution was spin-coated between the perovskite layer and the hole transport layer (spiro-OMeTAD), and the resulting device was annealed at 190 °C. The DPPS-treated devices had higher conversion efficiencies than the standard one, and they were stable in ambient air. Microstructural observations suggested that DPPS would work effectively as a bulk-hetero structure along with perovskite layers.