Interfacial Defect Passivation and Stress Release via Multi-Active-Site Ligand Anchoring Enables Efficient and Stable Methylammonium-Free Perovskite Solar Cells

Abstract

Interfacial trap-assisted non-radiative recombination and residual stress impede the further increase of power conversion efficiency (PCE) and stability of the methylammonium-free (MA-free) perovskite solar cells (PSCs). Here, we report an interfacial defect passivation and stress release strategy through employing the multi-active-site Lewis base ligand (i.e., (5-mercapto-1,3,4-thiadiazol-2-ylthio)­acetic acid (MTDAA)) to modify the surface and grain boundaries (GBs) of MA-free perovskite films. Both experimental and theoretical results confirm strong chemical interactions between multiple active sites in the MTDAA molecule and undercoordinated Pb2+ at the surface or GBs of perovskite films. It is demonstrated theoretically that multi-active-site adsorption is more favorable thermodynamically as compared to single-active-site adsorption, regardless of PbI2 termination and formamidinium iodide (FAI) termination types. MTDAA modification results in much reduced defect density, increased carrier lifetime, and almost thoroughly released interfacial residual stress. Upon MTDAA passivation, the PCE is boosted from 20.26% to 21.92%. The unencapsulated device modified by MTDAA maintains 99% of its initial PCE after aging under the relative humidity range of 10–20% for 1776 h, and 91% after aging at 60 °C for 1032 h.

Self‐Formed Multifunctional Grain Boundary Passivation Layer Achieving 22.4% Efficient and Stable Perovskite Solar Cells

“…. [24,34,35] Obviously, the perovskite film with K 2 SO 4 (1176.7 ns) presents a much longer carrier lifetime compared with the control film (889.7 ns), which is in good accordance with enhanced PL intensity. The results are well consistent with PL intensity as reflected by PL mapping of the perovskite films without and with K 2 SO 4 in Figure 2g,h.…”

“…(Figure 2f ). The equation of double-exponential function used for fitting TRPL curves is expressed as [24,34,35] where A 1 and A 2 represent the amplitude of the fast and slow decay process, respectively. τ 1 and τ 2 are the fast and slow decay time constants, respectively.…”

“…As can be seen from the dark I-V curves of the glass/ITO/perovskite without or with K 2 SO 4 /Au in Figure 2i, we can find three evident regions (i.e., Ohmic region at low bias, trap-filled limit region at intermediate bias, and trap-free SCLC region at high bias). The defect density was obtained according to the equation of n t ¼ (2εε 0 V TFL )/(eL 2 ), [34,36,37] where ε 0 is the vacuum dielectric constant, ε is the dielectric constant of the perovskite, V TFL is the trap-filled limiting voltage, e is the elementary charge, and L is the thickness of the perovskite films. The control perovskite film has a defect density of 2.03 Â 10 15 cm À3 , which is much higher than that of the modified perovskite film (1.19 Â 10 15 cm À3 ).…”

“…Time‐resolved photoluminescence (TRPL) spectra were measured to study the carrier lifetimes of perovskite films (Figure 2f). The equation of double‐exponential function used for fitting TRPL curves is expressed as I ( t ) = I 0 + A 1 exp(− t / τ 1 ) + A 2 exp(− t / τ 2 ), [ 24,34,35 ] where A 1 and A 2 represent the amplitude of the fast and slow decay process, respectively. τ 1 and τ 2 are the fast and slow decay time constants, respectively.…”

White-light defect emission and enhanced photoluminescence efficiency in a 0D indium-based metal halide

“…Lead halide perovskites have emerged as one of the most promising classes of light absorbers for low-cost, efficient solar cells. 1–3 Their exceptional electronic and optical properties also encourage researchers to explore potential applications beyond solar cells. 4–8 In particular, low-dimensional organic–inorganic metal halides have been considered as efficient emitters due to the merits of structural and compositional tunability, extraordinary optical properties and facile synthesis by wet and solid-state methods, 9–17 which are potentially used in display technologies, solid-state lighting, scintillators, remote thermography and anti-counterfeiting labeling.…”