Effect of CH₃NH₃PbI₃thickness on device efficiency in planar heterojunction perovskite solar cells

Abstract

Recent advances in the development of perovskite solar cells based on CH 3 NH 3 PbI 3 have produced devices with power conversion efficiencies of >15%. While initial work in this area assumed that the perovskitebased cells required a mesoporous TiO 2 support, many recent reports have instead focused on the development of planar heterojunction structures. A better understanding of how both cell architecture and various design parameters (e.g., perovskite thickness and morphology) affect cell performance is needed. Here, we report the fabrication of perovskite solar cells based on a ZnO nanoparticle electron transport layer, CH 3 NH 3 PbI 3 light absorber, and poly(3-hexylthiophene) (P3HT) hole transport layer. We show that vapor-phase deposition of the PbI 2 precursor film produces devices with performances equivalent to those prepared using entirely solution-based techniques, but with very precise control over the thickness and morphology of the CH 3 NH 3 PbI 3 layer. Optimization of the layer thickness yielded devices with efficiencies of up to 11.3%. The results further demonstrate that a delicate balance between light absorption and carrier transport is required in these planar heterojunction devices, with the thickest perovskite films producing only very low power conversion efficiencies.

Fabrication of organic-inorganic perovskite thin films for planar solar cells via pulsed laser deposition

“…3(b)). This agrees well with a recent report 35 and suggests that the excess amount of MAI evaporates during the annealing process. Thus, the PLD of PbI 2 precursor allows the fabrication of organic-inorganic perovskite films with a precisely tailored thickness.…”

“…This enhanced roughness is due to the volume expansion when the perovskite phase is formed during the intercalation of MAI into the PbI 2 layer. 35 This in-situ growth process of organic-inorganic perovskite crystal also leads to a substantial increase in the grain size as shown in Fig. 2(c).…”

“…2(a) (bottom)). 6,7,35 A small XRD peak indicated by an asterisk corresponds to the (001) peak of PbI 2 , 34 We performed atomic force microscopy (AFM) to examine the morphology of our films. A 5 µm × 5 µm AFM image of a PbI 2 film prior to spin-coating of a MAI layer is shown in Fig.…”

“…Therefore, the thickness of the CH 3 NH 3 PbI 3 layer is an important device design parameter. 35 To demonstrate precise control of the thickness of the CH 3 NH 3 PbI 3 thin film using the PLD-based hybrid method, we deposited PbI 2 films with different thicknesses and compared them to the thicknesses and the composition of the final CH 3 NH 3 PbI 3 films. When the thickness of the starting PbI 2 thin films is in the range of 80 -280 nm, the thickness of the final CH 3 NH 3 PbI 3 thin films is found to be in the range of 185 -580 nm, as determined by profilometry.…”

Efficient hole-blocking layer-free planar halide perovskite thin-film solar cells

“…The thickness of the light-absorbing layer plays an important role in determining the performance of thin-film solar cells 34 . If the absorber layer is too thin, not enough light will be absorbed, which will lead to low current.…”