Enhanced Activation Energy Released by Coordination of Bifunctional Lewis Base d-Tryptophan for Highly Efficient and Stable Perovskite Solar Cells

Abstract

Perovskite defect passivation with molecule doping shows great potential in boosting the efficiency and stability of perovskite solar cells (PSCs). Herein, an efficient and low-cost bifunctional Lewis base additive d-tryptophan is introduced to control the crystallization and growth of perovskite grains and passivation defects. It is found that the additive doped in the solution precursors could retard crystal growth by increasing activation energy, resulting in improved crystallization of large grains with reduced grain boundaries, as well as inhibiting ion migration and PbI2 aggregation. As a result, the PSCs incorporated with d-tryptophan additives achieve an improved power conversion efficiency from 18.18 to 21.55%. Moreover, the d-tryptophan passivation agent improves the device stability, which retains 86.85% of its initial efficiency under ambient conditions at room temperature after 500 h. This work provides Lewis base small-molecule d-tryptophan for efficient defect passivation of the grain boundaries toward efficient and stable PSCs.

Potassium Salt Coordination Induced Ion Migration Inhibition and Defect Passivation for High-Efficiency Perovskite Solar Cells

“…22−24 According to the Lewis acid−base coordination theory, a Lewis base additive is considered as the cationic defect passivator due to its lone pair electrons, which could interact with cations by forming the coordination bond. 25,26 Typical Lewis base additives such as thiophene, pyridine, carboxyl derivatives, and amino acids have been reported to suppress the carrier nonradiative recombination and increase the carrier lifetime via defect passivation. 27,28 Meanwhile, the potential mechanism of controlling the annealing crystallization by forming a Lewis acid−base adduct is studied, with enhanced crystallinity, larger grain size, and fewer grain boundaries.…”

“…where A 1 and A 2 represent relative amplitudes and τ 1 and τ 2 are the lifetime of fast decay and slow decay. 25 The specific parameters are listed in Table S1; the average carrier lifetime is significantly extended from 415.58 to 869.51 ns after OAPS modification. This indicates that the nonradiative recombination has been suppressed significantly due to the reduced density of trap states.…”

“…To date, a lot of effort has been made to decline trap states, reduce grain boundaries, and inhibit ion migration, including solvent engineering, interface engineering, and additive engineering. − Among them, additive engineering is an effective strategy to passivate the trap states and improve perovskite film quality for the preparation of efficient and stable PSCs due to its low cost and simple process. − According to the Lewis acid–base coordination theory, a Lewis base additive is considered as the cationic defect passivator due to its lone pair electrons, which could interact with cations by forming the coordination bond. , Typical Lewis base additives such as thiophene, pyridine, carboxyl derivatives, and amino acids have been reported to suppress the carrier nonradiative recombination and increase the carrier lifetime via defect passivation. , Meanwhile, the potential mechanism of controlling the annealing crystallization by forming a Lewis acid–base adduct is studied, with enhanced crystallinity, larger grain size, and fewer grain boundaries. , For anion defects (uncoordinated I – , Pb–I antisite), the passivation strategy of Lewis acid is mainly focused on fullerene derivatives, in which the ability of the electron acceptor is attributed to strain of its spherical structure. − Besides the Lewis base and acid additive, the metal cations are also widely studied as the defect passivator in perovskites, including the alkali cations and transition metal cations such as Na + , K + , Cs + , Ni 2+ , and Eu 3+ . − Due to the charge of outermost valence electrons lost or gained, metal cations could interact with charged defects through electrostatic force. In addition, it is worth noting that K + could be energetically favorable to occupy the interstitial sites within the perovskite lattice with the appropriate radius of 1.38 Å, which hinders the formation of an iodide Frenkel defect caused by I – migration, eliminating the hysteresis of PSCs significantly .…”

“…In the TRPL spectrum, the charge carrier transport dynamic shows the same trend. To calculate the average lifetime, a double exponential decay curve is induced, as determined by eq where A 1 and A 2 represent relative amplitudes and τ 1 and τ 2 are the lifetime of fast decay and slow decay . The specific parameters are listed in Table S1; the average carrier lifetime is significantly extended from 415.58 to 869.51 ns after OAPS modification.…”

Consolidating a Pb–X framework via multifunctional passivation with fluorinated zwitterions for efficient and stable perovskite solar cells

“…33 It has been proven that passivators can effectively reduce ionic defects in the perovskite layer to improve the device efficiency, and improvements in stability against the effects of water and oxygen have also been extensively studied. [34][35][36][37][38] Cai et al incorporated the uorinecontaining molecule 2,2-diuoropropanediamide (DFPDA) into the perovskite layer; this not only formed bridges between the perovskite layer and transport layer for efficient charge transport, but it also resulted in high hydrophobicity to improve the environmental stability of the PSC. 39 Although previous studies have conrmed the benets of zwitterions and uorine on ionic defect passivation and stability against humidity, few studies have considered the synergistic passivation effects of uorine and zwitterions on ionic passivation and enhancing the stability against humidity.…”