Effects of a Molecular Monolayer Modification of NiO Nanocrystal Layer Surfaces on Perovskite Crystallization and Interface Contact toward Faster Hole Extraction and Higher Photovoltaic Performance

Abstract

NiO is a promising hole transporting material for perovskite solar cells due to its high hole mobility, good stability, easy processibility, and suitable Fermi level for hole extraction. However, the efficiency of NiO‐based cells is still limited by the slow hole extraction due to the poor perovskite/NiO interface and the inadequate quality of the two solution‐processed material phases. Here, large influences of a monolayer surface modification of NiO nanocrystal layers with ethanolamine molecules are demonstrated on the enhancement of hole extraction/transport and thus the photovoltaic performance. The underlying causes have been revealed by a series of studies, pointing to a favorable dipole layer formed by the molecular adsorption along with the enhanced perovskite crystallization and the improved interface contact. Comparatively, the solar cells based on a diethanolamine‐modified NiO layer have achieved a rather high fill factor, indeed one of the highest among NiO‐based perovskite solar cells, and high short‐circuit photocurrent density (Jsc), resulting in a power conversion efficiency of ≈16%, most importantly, without hysteresis.

Effect of Carrier Transport in NiO on the Photovoltaic Properties of Lead Iodide Perovskite Solar Cells

“…The valence band edge (E VB ) of NiO x has been reported to vary from 5.05 to 5.5 eV and depends on the surface condition of NiO x . 19,22,25,26,33,37 The surface condition of NiO changes due to exposure to air or by surface treatments. The open circuit voltage (V OC ) is determined by the difference between the E VB of NiO x and the conduction band of PCBM.…”

“…NiO x has been introduced as the HTM and electron blocking layer for perovskite solar cells to improve the stability of the device by place from organic HTM to inorganic HTM. [19][20][21][22][23][24][25][26][27][28][29] The valence band edge (E VB ) of NiO x is also energetically matched with that of perovskite. 19,22,25,26,33 The transmittance of NiO x is very high in the visible region because the band gap of NiO is over 3.0 eV.…”

“…[19][20][21][22][23][24][25][26][27][28][29] The valence band edge (E VB ) of NiO x is also energetically matched with that of perovskite. 19,22,25,26,33 The transmittance of NiO x is very high in the visible region because the band gap of NiO is over 3.0 eV. The metals other than Ni or other inorganic metal oxides have been introduced into NiO x because of low conductivity of NiO x .…”

“…15 Recently, several hole transport materials (HTM) have also been introduced into the perovskite solar cells in place of PEDOT:PSS to obtain probable device application or efficient devices. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] The typical requirements for HTMs of perovskite solar cells are as follows.…”

Investigation of NiOx-hole transport layers in triple cation perovskite solar cells

“…However, for fast and large scale roll-to-roll fabrication, coating or printing processes for the application of the NiO x films are of interest. In this regard, several methods using spin coating followed by an additional annealing step are reported [23][24][25]. Interestingly, higher temperature treatment of the NiO x films significantly affects the device performance.…”