Spontaneous Interface Ion Exchange: Passivating Surface Defects of Perovskite Solar Cells with Enhanced Photovoltage

Abstract

Interface engineering is of great concern in photovoltaic devices. For the solution‐processed perovskite solar cells, the modification of the bottom surface of the perovskite layer is a challenge due to solvent incompatibility. Herein, a Cl‐containing tin‐based electron transport layer; SnOx‐Cl, is designed to realize an in situ, spontaneous ion‐exchange reaction at the interface of SnOx‐Cl/MAPbI3. The interfacial ion rearrangement not only effectively passivates the physical contact defects, but, at the same time, the diffusion of Cl ions in the perovskite film also causes longitudinal grain growth and further reduces the grain boundary density. As a result, an efficiency of 20.32% is achieved with an extremely high open‐circuit voltage of 1.19 V. This versatile design of the underlying carrier transport layer provides a new way to improve the performance of perovskite solar cells and other optoelectronic devices.

Simultaneous Contact and Grain‐Boundary Passivation in Planar Perovskite Solar Cells Using SnO2‐KCl Composite Electron Transport Layer

“…Pang and co‐workers controlled the hydrolysis process of SnCl 4 to synthesize the chlorine‐capped SnO 2 nanocrystal colloids for the ETL. The ion exchange between Cl (from SnO x ) and I (from perovskite) could rearrange the interface structure and reduce the interfacial recombination …”

Graphene‐Based Materials in Planar Perovskite Solar Cells

“…[ 162 ] The extraction of electrons and holes originates at the ETL/PSK and the HTL/PSK interfaces, and the charge transport through the heterointerfaces of CTL/PSK is doomed to cause charge loss due to defects at the heterointerfaces. [ 163,164 ] With regard to the common spin‐coating method, the CTLs at the bottom of perovskite layers have an extraordinary effect on the crystallization of perovskite, whereas the CTLs at the top of perovskite layers directly contact the grain boundaries and dangling bonds on the surface of perovskite. [ 165 ] Due to their promising designability, graphene‐based interlayers have emerged as viable options for defect passivation at the interface between CTLs and PSKs.…”

Solvent‐Actuated Self‐Assembly of Amphiphilic Hole‐Transporting Polymer Enables Bottom‐Surface Passivation of Perovskite Film for Efficient Photovoltaics

“…Even though a passivation layer can be additionally deposited on the charge transporting layer, it will be destroyed by the polar solvents usually used for the subsequent perovskite deposition owing to high polarity of most of passivation molecules containing hydroxyl, carboxyl, amino, ammonium, and so on. [5,[8][9][10][11] Therefore, it is significant to develop a charge transporting film with passivation groups strongly grafted on the surface while keeping undamaged after the perovskite deposition.…”

“…For this purpose, Tan et al and Pang et al have separately reported that chlorine-modified TiO 2 or SnO 2 nanocrystals are used as electron transporting layer (ETL) in n-i-p type PSCs, where the chlorine ions locate on the ETL surface to passivate defects of upper perovskite layer for improved device performances. [6,9,10] However, this strategy is not applicable to preceding organic passivation groups because weak interactions between these intrinsically incompatible organic groups and inorganic charge transporting compounds cannot guarantee the polar organic species in good conditions when depositing Bottom-surface defect passivation of perovskite film, lagging far behind easily conducted bulk and top-surface passivations in perovskite solar cells (PSCs), remains rather challenging because most passivation molecules/groups can be eroded by polar solvents used for the subsequent perovskite deposition. In this work, an effective bottom-surface passivation is enabled for enhanced performance of inverted PSCs by covalently attaching a passivation group (hydroxyl) to a hole transporting polymer.…”

“…have separately reported that chlorine‐modified TiO 2 or SnO 2 nanocrystals are used as electron transporting layer (ETL) in n‐i‐p type PSCs, where the chlorine ions locate on the ETL surface to passivate defects of upper perovskite layer for improved device performances. [ 6,9,10 ] However, this strategy is not applicable to preceding organic passivation groups because weak interactions between these intrinsically incompatible organic groups and inorganic charge transporting compounds cannot guarantee the polar organic species in good conditions when depositing the perovskite layer. It is thus still highly challenging to implement the bottom‐surface passivation of perovskite film by employing those widely used organic passivation groups.…”