Trap State Passivation by Rational Ligand Molecule Engineering toward Efficient and Stable Perovskite Solar Cells Exceeding 23% Efficiency

Abstract

long carrier diffusion lengths, adjustable bandgaps, and low-cost fabrication. [1][2][3] Until now, the certified power conversion efficiency (PCE) has reached 25.5%, [4] making the PSC a promising candidate for the next-generation thin-film solar cells. [3,5] However, the presently obtained record PCE is still far from Shockley-Queisser limit efficiency. [6] In addition, the currently achieved stability is much lower below the standard of commercial application. It is well known that poor perovskite film quality is one of the main reasons for efficiency and stability losses. Consequently, it is highly expected to minimize the trap-assisted nonradiative recombination losses via improving perovskite film quality.The traditional solution method with fast crystallization and high-temperature annealing process would inevitably lead to a variety of defects in perovskite bulk and at the surfaces and grain boundaries (GBs). [7][8][9] Most defects in the bulk of perovskite films are shallow-level defects, while most defects at the surface and GBs of perovskite films are deep-level defects, which is detrimental to device performance through capturing carriers. [6,10,11] Moreover, these defects would provide pathways for ion migration, which results in efficiency and stability losses. [6,12,13] In addition, water and oxygen would preferentially attack the surface and GBs of perovskiteThe nonradiative recombination losses resulting from the trap states at the surface and grain boundaries directly hinder the further enhancement of power conversion efficiency (PCE) and stability of perovskite solar cells. Consequently, it is highly desirable to suppress nonradiative recombination through modulating perovskite crystallization and passivating the defects of perovskite films. Here, a simple and effective multifunctional additive engineering strategy is reported where 11 Maleimidoundecanoic acid (11MA) units with carbonyls (carboxyl and amide) and long hydrophobic alkyl chain are incorporated into a perovskite precursor solution. It is revealed that improved crystallinity, reduced trap state density, and inhibited ion migration are achieved, which is ascribed to the strong coordination interaction between the carbonyl groups at both sides of 11MA molecules and Pb 2+ . As a result, improved efficiency and stability are achieved simultaneously after introducing 11MA additive. The device with 11MA additive delivers a champion PCE of 23.34% with negligible hysteresis, which is significantly higher than the 18.24% of the control device. The modified device maintains around 91% of its initial PCE after aging under ambient conditions for 3000 h. This work provides a guide for developing multifunctional additive molecules for the purpose of simultaneous improvement of efficiency and stability.

Polyacrylonitrile‐Coordinated Perovskite Solar Cell with Open‐Circuit Voltage Exceeding 1.23 V

“…Chemie elements in the sample. [13,23] High-resolution XPS spectrum of the Pb 4f for the control film shows two main peaks located at 138.46 and 143.35 eV, corresponding to the Pb 4f 7/ 2 and Pb 4f 5/2 , respectively (Figure 1d), whereas the PANpassivated (PVSK-PAN) film shows two main peaks at 137.35 and 142.15 eV. It was found that the Pb 4f peak of the PVSK-PAN film shifted 1.2 eV to the lower binding energy.…”

Polyacrylonitrile‐Coordinated Perovskite Solar Cell with Open‐Circuit Voltage Exceeding 1.23 V

“…elements in the sample. [13,23] High-resolution XPS spectrum of the Pb 4f for the control film shows two main peaks located at 138.46 and 143.35 eV, corresponding to the Pb 4f 7/ 2 and Pb 4f 5/2 , respectively (Figure 1d), whereas the PANpassivated (PVSK-PAN) film shows two main peaks at 137.35 and 142.15 eV. It was found that the Pb 4f peak of the PVSK-PAN film shifted 1.2 eV to the lower binding energy.…”

“…[9] It has been demonstrated that additive engineering is a feasible and effective strategy to passivate defects. [10] Functional group containing N, O, or S atoms usually has a lone pair of electrons, such as pyridine, [11] thiophene, [12] and alkyl acids, [13] etc., which can interact with these positively charged defects in perovskite films. In the past, polymer [14] additives containing carbonyl group (C=O) [15] have been widely studied due to their high stability and reliable interaction with the perovskite grains.…”

Defect Passivation Using Trichloromelamine for Highly Efficient and Stable Perovskite Solar Cells

“…The PCE of PSC increased from 18.85 to 20.72% [ 25 ]. After adding maleimide undecanoic acid (11MA) to the perovskite precursor solution, the density of trap states in perovskite layer reduced due to the strong coordination interaction between 11MA and Pb 2+ , resulting in the increase of PCE from 18.24 to 23.34% [ 26 ]. The additive molecules with π-conjugated structure are more likely to gather at the perovskite GBs, inducing the interconnection of the perovskite grains and therefore the more stable PSC [ 27 ].…”