Modification of perovskite/HTL interface with cooperative polymers bilayer (PTB7-Th/P3HT) to improve perovskite solar cell efficiency and stability

The use of interlayers is a valuable strategy for improving the performance of perovskite solar cells. Usually, such interlayers are thin films of a single material. We consider it interesting to evaluate interlayers formed by two or more materials, to take advantage of their possible cooperative or complementary effect. In the present work, the influence of monolayers and bilayers of the polymers PTB7-Th and P3HT, placed in perovskite/Spiro-OMeTAD interface, is evaluated on the efficiency and stability of solar cells. Devices with the perovskite film made in air (R Cells), and devices with the perovskite made in 2 atm (PbI2 deposition in N2, and CH3NH3I deposition in air) (S Cells) were studied. It is observed that polymer monolayers and bilayers create more compact surfaces, reduce recombination and leakage currents, and promote hole transfer from perovskite. The incorporation of these intermediate layers significantly increases the efficiency of R cells, but less in S cells. With the PTB7-Th/P3HT bilayer, the highest efficiency is achieved in R cells with an increase of 172%, compared with the efficiency of the control cell. On the other hand, with the P3HT interlayer, the highest efficiency is achieved in S cells and the highest stability in both types of cells (R and S). This study suggests that the use of interlayers formed by bilayers of organic materials is an interesting way to improve the performance of perovskite solar cells.