Compact and functional co-self-assembled monolayers for efficient inverted wide-bandgap perovskite solar cells

Abstract

Wide-bandgap perovskite solar cells (PSCs) have garnered significant attention owing to their potential for use in tandem structures, indoor photovoltaics, and related applications. However, wide-bandgap PSCs still face notable challenges, including substantial open-circuit voltage loss and inferior perovskite film quality, mainly due to the imperfection of the hole transport layer at the buried interface. Herein, we synthesize a cyanation-functionalized self-assembled monolayer material, CN-4PACz, and blend it with Me-4PACz to construct a co-assembled monolayer material (co-SAM) as the hole transport layer in wide-bandgap PSCs. The cyano group attached onto CN-4PACz endows it with a deeper highest occupied molecular orbital energy level, larger molecular dipole moment and stronger adsorption energy on the perovskite. Thus, the co-SAM presents improved energy level alignment with the perovskite, higher surface energy, enhanced defect passivation capacity, increased electrical conductivity and more uniform morphology compared with Me-4PACz. The perovskite film deposited on co-SAM layers presents improved crystal quality with a larger grain size, more uniform morphology, and reduced interfacial defects, which help inhibit trap-assisted recombination and benefit charge transport and extraction in devices. Consequently, wide-bandgap PSCs having the co-SAM layer achieve an impressive power conversion efficiency of 18.41% with a higher open-circuit voltage of 1.339 V and a fill factor of 83.08%, outperforming the control device with Me-4PACz (17.45%). The efficiency of 18.41% is among the highest values for wide-bandgap (>1.86 eV) PSCs so far. This work highlights an efficient approach for developing high-performance self-assembled monolayer materials, offering a promising pathway toward advancing wide-bandgap PSCs and their application in tandem solar cells.