Constructive molecular configurations for surface-defect passivation of perovskite photovoltaics

Abstract

Surface trap–mediated nonradiative charge recombination is a major limit to achieving high-efficiency metal-halide perovskite photovoltaics. The ionic character of perovskite lattice has enabled molecular defect passivation approaches through interaction between functional groups and defects. However, a lack of in-depth understanding of how the molecular configuration influences the passivation effectiveness is a challenge to rational molecule design. Here, the chemical environment of a functional group that is activated for defect passivation was systematically investigated with theophylline, caffeine, and theobromine. When N-H and C=O were in an optimal configuration in the molecule, hydrogen-bond formation between N-H and I (iodine) assisted the primary C=O binding with the antisite Pb (lead) defect to maximize surface-defect binding. A stabilized power conversion efficiency of 22.6% of photovoltaic device was demonstrated with theophylline treatment.

Multifunctional Phosphorus‐Containing Lewis Acid and Base Passivation Enabling Efficient and Moisture‐Stable Perovskite Solar Cells

“…Intrinsically, A‐site cations contribute to thermal, light exposure, moisture, and mechanical stabilities, while mixed halides are found to produce more reproducible and thermally stable films with higher crystal qualities. [ 2–5 ] The MLMP Cs 0.05 MA 0.15 FA 0.8 Pb(I 0.83 Br 0.17 ) 3 with an amazing high PCE over 20% and an improved stability was first reported in 2016. [ 6,7 ] Recently, Amassian et al revealed their crystallization behaviors using an in situ time‐resolved grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) technique.…”

“…Different kinds of functional molecules including Lewis acid and base, alkylammonium halide, and wide bandgap and hydrophobic polymers can passivate perovskite surface acting as interfacial modification layers. [ 2,18–27 ] However, it is still difficult to accurately identify defect types including Pb 2+ /halide vacancies, interstitial Pb 2+ /halides, and undercoordinated Pb 2+ /halides for these multicomponent perovskites. [ 11,28–30 ] Therefore, identifying defect types and adopting suitable passivators are crucial not only to boost the efficiency but also to slow down the moisture degradation.…”

How machine learning can help select capping layers to suppress perovskite degradation

“…On the other hand, x log P or partition coefficient (an indicator for hydrophobicity), complexity, and the number of carbons, iodines, or bromines generally have lower ranks in the model. If we consider the recently published capping layer materials, such as theophylline, caffeine, and theobromine, 15,16 assuming they were fabricated in the same manner as the materials in this study, the onsets are predicted to happen at 98, 309, and 105 minutes respectively. As a reference, PTEAI onset happens at (460 ± 110) minutes.…”

“…Due to its lower number of hydrogen-bond donor and smaller polar surface area, caffeine is predicted to be more stable among these 3 materials, even though its surface passivation property is worse than theophylline. 15…”

“…8 Perovskite thin-film deposition with a range of organic halides has been reported, including benzene rings/ phenyl with amine (e.g. phenylethylammonium iodide, [9][10][11] phenylethylammonium bromide, 9,12 aniline iodide, 13,14 benzylammonium iodide, 14 teophylline, 15 caffeine 16 ), long carbon chains with amine (e.g. n-butylammonium iodide, 17,18 n-octylammonium iodide 18 ), fluorous amine (e.g.…”