Grain structure control and greatly enhanced carrier transport by CH₃NH₃PbCl₃ interlayer in two-step solution processed planar perovskite solar cells

We report that the use of a CH₃NH₃PbCl₃ interlayer onto the PEDOT:PSS layer in the two-step solution deposition of CH₃NH₃Pbl₃ for planar p-i-n type perovskite solar cells (PSCs) can lead to a dramatic enhancement of short-circuit current density (J_sc) by 52.8% from 13.07 mA cm⁻² to 19.98 mA cm⁻². While the absorption and thus the composition of the perovskite layers remain unchanged, Incident photon-to-current efficiency (IPCE) measurement results reveal much enhanced carrier transport, which in turn can be correlated to the larger and more columnar grain structure in the perovskite layer with the use of the CH₃NH₃PbCl₃ interlayer. On the other hand, the two-step solution processed perovskite layers without the CH₃NH₃PbCl₃ interlayer exhibit smaller and more cross-hatching grain structure and yield significantly smaller J_sc. Therefore our results revealed clearly that the insertion of CH₃NH₃PbCl₃ interlayer, which affects the nucleation dynamics, may control the grain structure of the two-step solution processed perovskite layers and improve dramatically the photovoltaic performance of the resultant planar p-i-n type PSCs. Our CH₃NH₃PbCl₃ interlayer may thus serve as an effective method for p-i-n PSCs to achieve high J_sc with thicker perovskite layer.