Defect Passivation via the Incorporation of Tetrapropylammonium Cation Leading to Stability Enhancement in Lead Halide Perovskite

Abstract

Improving the performances of photovoltaic (PV) devices by suppressing nonradiative energy losses through surface defect passivation and enhancing the stability to the level of standard PV represents one critical challenge for perovskite solar cells. Here, reported are the advantages of introducing a tetrapropylammonium (TPA + ) cation that combines two key functionalities, namely surface passivation of CH 3 NH 3 PbI 3 nanocrystals through strong ionic interaction with the surface and bulk passivation via formation of a type I heterostructure that acts as a recombination barrier. As a result, nonencapsulated perovskite devices with only 2 mol% of TPA + achieve power conversion efficiencies over 18.5% with higher V OC under air mass 1.5G conditions. The devices fabricated retain more than 85% of their initial performances for over 1500 h under ambient conditions (55% RH ± 5%). Furthermore, devices with TPA + also exhibit excellent operational stability by retaining over 85% of the initial performance after 250 h at maximum power point under 1 sun illumination. The effect of incorporation of TPA + on the structural and optoelectronic properties is studied by X-ray diffraction, ultraviolet-visible absorption spectroscopy, ultraviolet photon-electron spectroscopy, time-resolved photoluminescence, and scanning electron microscopy imaging. Atomic-level passivation upon addition of TPA + is elucidated employing 2D solid-state NMR spectroscopy.

Interfaces in metal halide perovskites probed by solid-state NMR spectroscopy

“…ssNMR has been used to study how a few of these salts, including choline, ethylammonium (EA), imidazolium, guanidinium (G) and tetrapropylammonium iodide (TPA), can passivate defects in MHPs. 375,[378][379][380][381][382] One important question presented by passivated MHPs is how the passivating agents incorporate within the device. Do the passivating salts mix microscopically with MHP grains, form a layer at the surface of the MHP lm, or segregate away from the MHP layer?…”

“…Nevertheless, 2D ssNMR spectroscopy has been applied to investigate the local proximities and interactions between MHP surfaces and passivating agents, and to elucidate the microscopic mechanisms of surface passivation. 375,378,379,381,382 Unlike the 2D 1 H-1 H DQ-SQ correlation experiment that probes through-space 1 H-1 H proximities within 5 A, the 2D 1 H-1 H SD experiment extends the length scale from sub-nanometer to several nanometers, and is thus well-suited to gain insight into intermolecular interactions and passivation mechanism in surface-modied MHPs.…”

High‐Performance and Industrially Viable Nanostructured SiOx Layers for Interface Passivation in Thin Film Solar Cells

“…Furthermore, SiO x has the potential to be used as a passivation layer in other thin film technologies, such as CdTe, Cu 2 ZnSnS 4 (CZTS), or perovskites, which could allow for an effective defect passivation. [ 36–47 ]…”

Multimodal host–guest complexation for efficient and stable perovskite photovoltaics

“…Moreover, the performance is still limited by defects and impurities that enhance non-radiative recombination of photogenerated charge carriers [7][8][9][10][11][12] . Conventional passivation is an effective strategy to remove defects from the surface of films 8,[13][14][15] , yet a number of defects remain in the bulk and it is vital to mitigate both types of defects. Formamidinium lead iodide (FAPbI 3 ) and FAPbI 3 -rich perovskites are particularly preferred for photovoltaic applications due to their superior optoelectronic properties and thermal stability 5 .…”