Improved Perovskite Film Growth on Spiro-OMeTAD with Alumina Deposited by Atomic Layer Deposition

Early progress in advancing the record efficiency of perovskite (PVSK) solar cells was made using the n–i–p structure with spiro-OMeTAD as the hole transport layer (HTL). However, only moderate performance has been achieved with spiro-OMeTAD as the HTL in the p–i–n structure. In this work we investigate the growth of alumina by atomic layer deposition (ALD) on a spiro-OMeTAD HTL and show improved perovskite film growth when the deposition is optimized. The film growth and device performance were examined with current–voltage analysis, scanning electron microscopy, X-ray diffraction, steady-state and time-resolved photoluminescence, Fourier transform infrared spectroscopy, and spectroscopic ellipsometry. When the ALD process was optimized, high-quality perovskite films were produced that led to a doubling in the average device efficiency of the p–i–n device with spiro-OMeTAD as the HTL. The improvements are attributed to better PVSK film growth rather than to significant reductions in nonradiative recombination.