Active layer thickness dependence of optoelectronic performance in CH3NH3PbI3 perovskite-based planar heterojunction photodiodes

This work investigates active layer thickness dependence of the morphology, crystallinity and optoelectronic performance of CH3NH3PbI3 perovskite-based planar heterojunction photodiodes (PDs). Surface morphology, average grain size, and crystalline size were monotonically improved with increasing the perovskite film thickness. However, the device performance was dramatically affected by enlarging the perovskite film thickness. Increasing the perovskite film thickness from 300 nm to 450 nm initially raised the device performance from (detectivity (D): 8.13 x 1010 Jones) to (D: 1.42 x 1012 Jones), as a result of the reduced recombination losses and improved charge transport properties due to the superior surface morphology, larger grain size and improved crystallinity. Nevertheless, the performance drops again (D: 2.0x1011 Jones) when the thickness was increased to 600 nm, which can be attributed to reduced absorbance, increased charge recombination and the reduced collection efficiency. An unexpected reduction in absorbance and exceptionally poor charge collection efficiency can be possibly related to the remnant excess PbI2, as inferred from x-ray diffraction analysis.