Research On High-Efficiency Tandem Solar Cells Based On Dimensional Control

In recent years,organic-inorganic hybrid perovskite solar cells（PSCs）have attracted great attention with power conversion efficiency surged from 3.8% to 25.7% at present,and have become research hot topic in the field of novel photovoltaics.The rapid development of PSCs benefits from the excellent optoelectronic properties and tunable bandgaps of perovskite materials.To further break through the bottleneck of power conversion efficiency of PSCs,perovskite materials are overlaid with other lightabsorbing semiconducting materials with different solar spectrum coverages to form tandem solar cells.In general,wide-bandgap top cells within the tandem devices first absorb the sunlight with short wavelengths,with the narrow-bandgap bottom cells then absorbing the sunlight with long wavelengths,thus realizing a multiband photoelectric response to the solar spectrum.Due to the tunable bandgaps of perovskite materials,their absorption regions can be complementary to the absorption range of silicon to form perovskite-silicon tandem solar cells.In order to match the absorption range of silicon solar cells,bandgap of perovskite material needs to be controlled at around 1.68 e V.However,reaching such bandgap through composition engineering in the way of introducing Br-tends to lead to compositional and phase segregation,which therefore negatively affects the photovoltaic performance and stability of the resultant solar cell devices.This work focuses on the phase stability of perovskite by coming up with a control strategy of structural dimension.By introducing large cations into the perovskite lattice,material structures with layered two-dimensional characteristics are formed that can effectively inhibit ion migration within the bulk of perovskites,thus improving the material stability and suppressing phase separation.Owing to the quantum well effects within the two-dimensional perovskites that hinder carrier transport,solar cell performance is however severely compromised.By further adopting a pre-buried two-dimensional bottom layer,the growth mode of two-dimensional structures within the perovskite film is effectively controlled,where these two-dimensional structures diffuse into the bulk of perovskite during post-annealing,forming two-dimensional/three-dimensional structures at the bottom interface.This type of structure can generate built-in electric field and improve carrier transport efficiency.Based on this structural modification,perovskite-silicon tandem solar cells with opencircuit voltage of 1.81 V and power conversion efficiency of 24.4% are fabricated.Furthermore,tandem device maintains 95% of initial efficiency after storage in an air atmosphere with 30% humidity,25 ℃ for 800 h.This work achieves stable perovskitesilicon tandem solar cells while obtaining good photovoltaic performance,and provides a solution to the problem of broadband perovskite instability in tandem solar cells,which is conducive to advancing the further commercialization of perovskite-silicon tandem solar cells.