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# Rationally tailored passivation molecules to minimize interfacial energy loss for efficient perovskite solar cells

Taoran Geng, Jike Ding, Zuolin Zhang, Mengjia Li, Hongjian Chen, Thierry

Pauporté, Rundong Wan, Jiangzhao Chen, Cong Chen

► To cite this version:

Taoran Geng, Jike Ding, Zuolin Zhang, Mengjia Li, Hongjian Chen, et al. Rationally tailored passivation molecules to minimize interfacial energy loss for efficient perovskite solar cells. Moore and More, 2025, 2, pp.9. 10.1007/s44275-025-00026-3. hal-05377996

HAL Id: hal-05377996

https://hal.science/hal-05377996v1

Submitted on 22 Nov 2025

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# Rationally tailored passivation molecules to minimize interfacial energy loss for efficient perovskite solar cells

Taoran Geng<fnref n="1" /> · Jike Ding<fnref n="1" /> · Zuolin Zhang<fnref n="1" /> · Mengjia Li<fnref n="1" /> · Hongjian Chen<fnref n="1" /> · Thierry Pauporte<fnref n="2" /> · Rundong Wan<fnref n="3" /> · Jiangzhao Chen<fnref n="3" /> · Cong Chen<fnref n="1" /> ID

Received: 27 October 2024 / Revised: 2 January 2025 / Accepted: 6 January 2025

© The Author(s) 2025

## Abstract

Labor-intensive, trial-and-error methods are frequently employed for modifying the perovskite surface to mitigate trap defects. There is an urgent need for rationally designed and efficient molecular passivators. To address the performance and stability challenges caused by defects in polycrystalline perovskite, we have rationally designed and tailored passivation molecules, 4-(trifluoromethyl)benzoic anhydride (TFBA), ethyl 4-(trifluoromethyl)benzoate (TFB), and 4-(trifluoromethyl)benzoic acid (PTF), to minimize interfacial energy loss and modulate the bandgap alignment for achieving efficient perovskite solar cells (PSCs). These molecules could target the perovskite surface defects, particularly Pb–I antisite defects, with the –COOH and trifluoromethyl functional groups at the edges. Among them, PTF exhibited superior passivation performance by coordinating its carboxyl group with Pb<fnref n="2" />⁺, effectively suppressing non-radiative recombination. Additionally, the fluorine sites in these molecules corrected lattice distortions and stabilized the perovskite structure through hydrogen bonding with MA/FA cations, reducing ion migration, and enhancing moisture resistance. As a result, PTF-modified PSCs achieved an efficiency of 25.57% and maintained over 85% of their initial efficiency after 1 600 h of aging. This study provides a clear pathway for optimizing passivation strategies through rational molecular design.

**Keywords** Perovskite solar cells · Rationally tailored passivator · Interfacial energy loss · Defect passivation · Energy band modulation

## 1 Introduction

Organic–inorganic metal halide perovskite solar cells (PSCs) have emerged as a highly promising photovoltaic technology due to their exceptional properties, including high power conversion efficiency (PCE), cost-effective fabrication, and suitability for flexible manufacturing [1, 2]. Since their initial development, the certified PCE of PSCs has dramatically increased from 3.8% in 2009 to over 26% [3, 4], approaching the performance of conventional silicon solar cells. This significant efficiency gain is largely attributed to the superior light-harvesting capability of the perovskite materials. However, the rapid crystallization in solution-processed polycrystalline perovskites introduces numerous defects, particularly at grain boundaries (GBs) and surfaces [1, 5, 6]. These defects, such as ion vacancies [7], interstitial species [8], and undercoordinated ions [9, 10], act as carrier recombination centers, limiting the open-circuit voltage (Voc) [11, 12] and accelerating the infiltration of moisture and oxygen, which undermines the long-term stability of PSCs. Additionally,

<footnote>Rundong Wan
rwan69@kust.edu.cn</footnote>

<footnote>Jiangzhao Chen
jzchen@kust.edu.cn</footnote>

<footnote>Cong Chen
chencong@hebut.edu.cn</footnote>

<footnote>Thierry Pauporte
thierry.pauporte@chimieparistech.psl.eu</footnote>

<footnote n="1">¹ State Key Laboratory of Reliability and Intelligence of Electrical Equipment, School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300401, China</footnote>

<footnote n="2">² Institut de Recherche de Chimie Paris (IRCP), UMR8247, Chimie ParisTech, PSL Research University, CNRS, 75005 Paris, France</footnote>

<footnote n="3">³ Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China</footnote>
methyl ammonium (MA)- or formamidinium (FA)-based perovskites, while efficient, are prone to structural degradation and phase transformation in the presence of heat and humidity, leading to the formation of PbI₂ and further defect generation [13–15]. These factors result in reduced light response characteristics and, in severe cases, complete efficiency loss. Consequently, substantial efforts have been made to mitigate these issues by passivating defects at the GBs and surfaces, thereby enhancing both the efficiency and stability of PSCs to meet the requirements for commercial viability. Further, surface defects and energy level mismatch of the perovskite/electron transporting layer can also lead to ion migration, hysteresis effects, and device degradation [16]. Therefore, it is crucial to address interface defects and adjust the interface energy band alignment through effective interface engineering to reduce interface energy losses.

Interface engineering [17–19] has become a widely adopted and effective strategy for optimizing the surface states of perovskite films, passivating trap defects, improving interfacial charge transport, and enhancing both the efficiency and stability of PSCs. A variety of passivation agents have been developed, with small organic molecules containing Lewis acid-base groups [20, 21], such as amide [22], amino [23], carbonyl [6, 21, 24], pyridine [25, 26], and fluorine [27], being particularly effective. These molecules can address trap states on the perovskite surface by interacting with halide anions or undercoordinated Pb²⁺ ions, which are especially prone to degradation in the presence of oxygen and moisture, leading to the formation of lead oxide and hydroxide species.

Among the surface defects, undercoordinated Pb²⁺ are of particular concern due to their sensitivity to environmental factors. Effective passivation strategies target these ions, with the carboxyl (–COOH) group being especially useful due to its ability to form strong Lewis acid–base interactions with Pb²⁺, thus preventing the formation of metallic lead clusters (Pb⁰). The introduction of –COOH-containing additives [6, 21, 24, 28, 29] for post-treatment and surface modification has been shown to reduce trap densities and extend carrier recombination times, ultimately inhibiting the V<sub>oc</sub> loss and improving the PCE of PSCs.

Additionally, fluorine-based compounds have been extensively explored for their hydrophobic properties, which enhance the moisture resistance and stability of PSCs. For example, Zhao et al. [27] utilized vapor-phase fluoride exposure to stabilize perovskite solar modules by forming strong lead–fluoride bonds, which suppressed defect formation and immobilized anions near the surface. Further, fluorinated passivating molecules, including poly(vinylidene fluoride) (PVDF) polymer [30], 4-(trifluoromethyl) benzoic acid (BA-CF3) [31], bi(trifluoromethyl) benzoic acid [32], 2,3,4,5,6-pentafluorobenzoic acid (5F-B) [33], hydrofluoric acid [34], fluorinated perylenediimide [35], etc., have been

applied to PSCs to achieve hydrophobic and chemical chelation effects. Given the complementary benefits of –COOH and fluorine, the development of multifunctional materials that incorporate both groups offers a promising approach to passivate undercoordinated Pb²⁺ while simultaneously protecting the perovskite film from environmental degradation.

In this study, we rationally tailored a series of fluorine-substituted small molecules to minimize interfacial energy loss by passivating interfacial defects and modulating the interfacial energy band alignment. The passivating molecules, including 4-trifluoromethylbenzoic acid (PTF), 4-trifluoromethylbenzoyl chloride (TFBA), and 4-trifluoromethylbenzyl acetate (TFB), were used to modify the top interface of perovskite films and act as effective shallow surface trap defect passivators in organic–inorganic hybrid PSCs. Although these three molecules had similar functional groups, there are differences in the number of active sites and the overall spatial configuration of the molecule, leading to the varied passivation effects. The strength of the passivation effects followed the order PTF > TFB > TFBA. Among these, PTF demonstrated an exceptional ability to reduce defect traps through the coordination of its carbonyl and fluorine groups with exposed Pb²⁺. By filling GBs and the surface of the perovskite film, PTF not only modified defects but also enhanced charge transport due to chelation between its carbonyl group and undercoordinated Pb²⁺. In addition to passivation, the introduction of PTF created a robust hydrophobic barrier that protected the perovskite film from moisture degradation. The fluorine groups also stabilized the perovskite structure by forming hydrogen bonds with MA/FA cations, effectively reducing ion migration. Compared to the control device, PSCs treated with PTF could achieve a PCE of 25.57%, with negligible hysteresis and an improved V<sub>oc</sub> of 1.18 V (compared to 1.14 V for the control). Furthermore, the moisture stability of the PTF-treated perovskite films was significantly enhanced, with unencapsulated devices retaining 82% of their initial PCE after 1 500 h of exposure to air, demonstrating superior ambient stability.

## 2 Results and discussion

Figure 1a shows the molecular structures of the TFBA, TFB, and PTF molecules for surface passivation in perovskite. To better grasp the electron density distribution, the electrostatic potential (ESP) of the molecules TFBA, TFB, and PTF was analyzed by the density functional theory (DFT) method. All three molecules contain fluorine groups, benzene rings, and C = O. Similarly, the three molecules all contain the same trifluoromethyl group at their ends, and the molecular design of the F-end will have a positive effect on the stability and coordination of perovskite. Specifically, TFBA has a symmetric spatial structure with a trifluoromethylbenzene

<figure><img src="image_3.png" /></figure>
<figure><img src="image_4.png" /><figcaption>**Fig. 1** **a** Chemical structures and electrostatic potential of TFBA, TFB, and PTF. **b** Schematic diagram of the interaction between passivation molecules and acceptor-like defects. **c** TFBA, TFB, and PTF with FAPbI₃ containing V₁ defects and PbI₁ defects. **d** The binding energy of TFBA, TFB, or PTF with FAPbI₃ containing PbI₁ antisite</figcaption></figure>

and V₁ defects. XPS spectra of e Pb 4f in control and TFBA, TFB, or PTF-modified perovskite films. FTIR for f TFBA+PbI₂, TFB+PbI₂, and PTF+PbI₂. g ¹H NMR spectra of FAI, TFBA, TFB, or PTF and their mixed solution

functional group, while both TFB and PTF are unidirectional molecules. Based on the trifluoromethylbenzene core, PTF has a –COOH functional group at its terminal end, whereas TFB contains an ethyl acetate group. The distinct spatial configurations of these three molecules allow for a deeper understanding and comparative analysis of how the number and position of functional groups influence passivation performance. Negative ESP is mainly distributed in –C=O, which is favorable for coordination with uncoordinated Pb²⁺ due to its strong electronegativity. The more electronegative

trifluoromethyl induces electrons to escape from the benzene ring, showing a positive ESP in the benzene ring, and this highly polarized molecule with strong electron delocalization will further enhance the interaction with the undercoordinated Pb²⁺.

As shown in Fig. 1b and S1, we speculated that the three passivators could interact with acceptor-like defects on the perovskite surface through ionic and hydrogen bonds, and are therefore anchored to the surface. The DFT calculations were then performed to understand the chemical interaction
between three rationally designed passivation molecules and the FAPbI₃ perovskite surface. We place the same molar number of molecules on the surface of FAPbI₃ perovskite crystals with I⁻ vacancies (Vᵢ) and Pb–I antisite defects Vₚb-I. Figure 1c, d shows the calculated binding energies of Vᵢ and Vₚb-I defects for the three molecules. For the chemical interaction with Vᵢ, the order of binding energy value is TFB (−12.91 eV) < PTF (−11.16 eV) < TFBA (−9.11 eV), meaning that TFB molecules exhibit the lowest binding ability to I vacancy defects, followed by that of PTF and TFBA. For Vₚb-I, PTF as passivator has the lowest binding energy of −16.34 eV, followed by TFBA of −12.47 eV, and TFB of −11.86 eV, showing a relatively large difference. This indicates that PTF interacts most prominently with the uncoordinated Pb²⁺ on the surface of perovskite through –COOH and F groups, thus achieving a better passivation effect. We hypothesize that the primary reason PTF molecules exhibit the lowest binding energy is that both the tri-fluoromethyl and carboxylic acid functional groups at either end can coordinate with Pb²⁺ simultaneously, without being hindered by steric effects from additional functional groups. In contrast, TFB has an extra –CH₂–CH₃ chain, which may obstruct its coordination with Pb²⁺. Although TFBA has a similar number of active sites as PTF, its binding capacity with defects could be compromised due to its spatial configuration. Therefore, in perovskite systems dominated by Pb–I antisite defects, the passivation effectiveness of these molecules likely follows the order: PTF > TFB > TFBA.

We analyzed the strength of its chemical interaction from an experimental perspective. Perovskite thin films were prepared using a one-step vacuum evaporation technique in ambient conditions. After the crystallization, TFBA, TFB, and PTF were then used for post-treatment. After TFBA, TFB, and PTF passivation, the X-ray photoelectron spectroscopy (XPS) peaks of Pb 4f (see Fig. 1f) moved in the direction of high binding energy, indicating that perovskite defects were modified by the C=O and F groups interacting with uncoordinated Pb²⁺ by coordination bonds. Compared to TFBA and TFB, the perovskite film containing PTF showed a larger binding energy shift, indicating that PTF interacted more strongly with the perovskite than TFBA or TFB. This is consistent with the theoretical results.

From the Fourier Transform Infrared spectroscopy (FTIR) results, the interaction between F and Pb caused the stretching vibration of the C–F bond at characteristic peaks at 1 322 cm⁻¹, 1 323 cm⁻¹, and 1 325 cm⁻¹. Meanwhile, the C=O stretching vibrations for TFBA, TFB, and PTF were observed at 1 725 cm⁻¹, 1 721 cm⁻¹, and 1 718 cm⁻¹, respectively, further indicating interactions with Pb²⁺. Fluorine is more electronegative than oxygen, so it is easy to associate with H atoms to form F…H hydrogen bonds. When modified molecules are added to perovskite, N–H…F hydrogen bonds in FA⁺ and MA⁺ are easily formed with N–H. Figure 1g

compares the proton nuclear magnetic resonance (¹H NMR) spectra of FAI, FAI+TFBA, FAI+TFB, and FAI+PTF in deuterated dimethyl sulfoxide d6 (DMSO-d6) solvent. After adding TFBA, TFB, or PTF, there were obvious changes in the chemical shift values of the hydrogen atoms in NH₂ and =NH₂⁺. After interacting FAI with TFBA, TFB, or PTF, the characteristic peak at 8.75 ppm of FAI moved to 8.92 ppm, 8.77 ppm, and 8.96 ppm, respectively. This phenomenon is attributed to the hydrogen bond interaction between the F and FA⁺, where the establishment of such hydrogen bonds serves to mitigate the formation of vacancy defects associated with FA⁺.

In order to further analyze the effect of passivation on the surface of perovskite, we conducted surface atomic force microscopy (AFM), Raman imaging spectroscopy, and grazing-incidence wide-angle X-ray scattering (GIWAXS) characterization for analyzing the morphology change. From the AFM images in Fig. 2a–d, it can be seen that the root-mean-square roughness (R_a) values for the control film and the TFBA-, TFB-, and PTF-modified films were 31.19 nm, 24.85 nm, 29.40 nm, and 21.87 nm, respectively. This indicates that after modification, the surface roughness of the films decreased, which can be a result of the reduced density of surface defect states, which is beneficial for carrier transport between interfaces. The PTF-modified film had the lowest R_a value, indicating the most effective passivation of the surface. Raman imaging spectroscopy (see Fig. 2e–h) results indicated that the Cs<sub>0.05</sub>MA<sub>0.05</sub>FA<sub>0.9</sub>PbI<sub>3</sub> perovskite films became more uniform after modification with TFBA, TFB, and PTF, suggesting a significant reduction in internal stress and defects. In particular, the GIWAXS diffraction spots of the PbI<sub>2</sub> phase in the control film are obvious at 0.07 nm<sup>-1</sup>, as is labeled in Fig. 2i. The GIWAXS results in Fig. 2i–l reveal that there was a significant PbI<sub>2</sub> peak in the control Cs<sub>0.05</sub>MA<sub>0.05</sub>FA<sub>0.9</sub>PbI<sub>3</sub> film, while the PbI<sub>2</sub> peak decreased after TFBA (see Fig. 2j), TFB (see Fig. 2k), and PTF (see Fig. 2l) modification, indicating a decrease in PbI<sub>2</sub> content. The reduction of PbI<sub>2</sub> can be further confirmed by X-ray diffraction (XRD) analysis (see Fig. 2m), in which the diffraction peak intensity of PbI<sub>2</sub> decreased after the introduction of TFBA, TFB, and PTF. From GIWAXS and XRD patterns, the PbI<sub>2</sub> diffraction peaks at 12.6° in the film were the lowest after PTF modification, indicating the most significant suppression of the PbI<sub>2</sub> phase.

Steady-State Photoluminescence (SSPL) and Time-
Resolved Photoluminescence (TRPL) were used to further
investigate the effect of defect passivation and the trap-
induced non-radiative recombination behavior of photo-
excited carriers in perovskite films. After PTF modifica-
tion, the fluorescence intensity significantly increased (see
Fig. 2n), indicating that non-radiative charge recombination
by the defects was suppressed. The luminescence intensity
of the perovskite films modified by TFBA and TFB also

<figure><img src="image_5.png" /></figure>
<figure><img src="image_6.png" /><figcaption>**Fig. 2** AFM images of the **a** control, **b** TFBA, **c** TFB, and **d** PTF-modified perovskite films. Raman imaging spectroscopy of the **e** control, **f** TFBA, **g** TFB, and **h** PTF-modified perovskite films. GIWAXS patterns of the **i** control, **j** TFBA, **k** TFB, and **l** PTF-modified perovskite film.</figcaption></figure>

**m** XRD for PbI₂, TFBA + PbI₂, TFB + PbI₂, and PTF + PbI₂. **n** Steady-state PL and **o** TRPL spectra of the control, TFBA, TFB, and PTF-modified perovskite films on a bare glass substrate

increased, but the enhanced intensity was slightly lower than that of PTF passivation. A bi-exponential fitting was applied to the TRPL curves (see Fig. 2o), and the fitting results were concluded in Table S1. Compared with the control perovskite film which had TRPL lifetime of 645.63 ns, the perovskite films modified by TFBA, TFB, and PTF exhibited longer average carrier lifetimes of 762.37 ns, 950.37 ns, and 2 533.25 ns.

We then systematically analyzed the effects of three rationally tailored molecules on the electronic states of

perovskite surfaces and their impact on changes in interfacial energy level structures. The surface potential of the control and modified perovskite films was measured using Kelvin probe force microscopy (KPFM). The contact potential difference (CPD) was recorded by measuring the electrostatic force between the conductive AFM tip and the film surface ($V_{tip}-V_{sample}$) [36]. Therefore, a higher CPD indicates a more negative surface potential, which suggests a gradual decrease in the surface work function, leading to enhanced n-type characteristics of the film surface. This not
only promotes electron transport but also creates a large hole transport barrier at the perovskite/ETL interface. ETL is the electron transport layer. As shown in Fig. 3a–h, the average CPD of the control, TFBA-, TFB-, and PTF-modified perovskite films is –383 mV, –232 mV, –221 mV, and –103 mV, respectively, indicating that the work function of the perovskite surface was decreased. Therefore, the modified films exhibited more n-type characteristics, which not only promoted electron transport but also hindered hole transfer at the Cs<sub>0.05</sub>MA<sub>0.05</sub>FA<sub>0.9</sub>PbI<sub>3</sub>/C<sub>60</sub> interface. The narrower distribution of CPD values on the surface of the PTF-modified perovskite indicated higher uniformity after treatment.

Ultraviolet photoelectron spectroscopy (UPS) analysis was then introduced to determine the Fermi level ($E_f$) and the valence band maximum (VBM) of the surfaces of the control, TFBA-, TFB-, and PTF-modified perovskite films. The optical bandgap was calculated to be $E_g$=1.53 eV (see Fig. S2) using the external quantum efficiency (EQE) measurements. After passivation, the secondary electron cutoff energy of the perovskite films shifted to higher binding energies (see Fig. 3i–l), indicating a higher Fermi level ($E_f$) and a decrease in work function. This was consistent with the results of KPFM. Importantly, in the modified films, the specific energy level alignment

<figure><img src="image_7.png" /><figcaption>**Fig. 3** KPFM images and corresponding potential distribution of the **a**, **e** control, **b**, **f** TFBA, **c**, **g** TFB, and **d**, **h** PTF-modified perovskite films. UPS spectra of the **i** control, **j** TFBA, **k** TFB, and **l** PTF-mod-</figcaption></figure>

ified perovskite films. Energy level diagram of the **m** control and **n** TFBA, **o** TFB, and **p** PTF-modified perovskite films

<figure><img src="image_8.png" /></figure>
facilitates the formation of an n–N homojunction and provides an additional built-in electric field directed from the surface to the bulk (see Fig. 3m–p). This contributed to an increased built-in potential (V<sub>bi</sub>), which in turn enhanced the V<sub>oc</sub> [37]. The magnitude of V<sub>bi</sub> is related to the difference (Δ) between the Fermi levels of the bulk and the surface. The Δ<sub>E</sub> value for PTF-modified perovskite films is 0.17 eV, which is greater than the Δ<sub>E</sub> values of 0.11 eV and 0.13 eV for TFBA and TFB-modified perovskite films, indicating the stronger built-in electric field at the Cs<sub>0.05</sub>MA<sub>0.05</sub>FA<sub>0.9</sub>PbI<sub>3</sub>/C<sub>60</sub> interface after PTF modification. This enhances electron transport and creates a higher hole barrier.

To investigate the impact of surface modification with TFBA, TFB, and PTF on solar cell performance, we fabricated inverted PSCs devices with the structure of ITO/ Me-4PACz/perovskite/passivation layer/C<sub>60</sub>/BCP/Ag, as shown in Fig. 4a. ITO is a transparent conductive glass. Me-4PACz is a Self-Assembled Monolayer, which usually refers to a layer of organic molecules modified on the surface of an electrode or perovskite film. BCP is an organic small molecule material and is often used as an electron transport layer modification material. Figure 4b shows the forward and reverse J–V curves of the control, TFBA-, TFB-, and PTF-modified perovskite-based PSCs devices. The corresponding photovoltaic parameters are listed in the Table S2. The PCE of the control PSCs device was 23.22%, with J<sub>sc</sub> of 25.59 mA/cm<sup>2</sup>, V<sub>oc</sub> of 1.14 V, and FF of 78.99%. While the best-performing TFBA-, TFB-, and PTF-modified PSCs devices showed PCEs of 24.22% (J<sub>sc</sub> 25.77 mA/cm<sup>2</sup>, V<sub>oc</sub> 1.17 V, FF 79.94%), 24.55% (J<sub>sc</sub> 25.96 mA/cm<sup>2</sup>, V<sub>oc</sub> 1.17 V, FF 80.40%), and 25.57% (J<sub>sc</sub> 26.22 mA/cm<sup>2</sup>, V<sub>oc</sub> 1.18 V, FF 82.54%), respectively. This indicates that the modification of PTF can achieve the highest efficiency improvement, followed by TFB and then TFBA. This sequential pattern is consistent with the passivation ability of Pb–I antisite defects in theoretical calculations and the chemical passivation ability in experimental XPS results. The hysteresis index [HI; HI=(PCE<sub>Reverse</sub> – PCE<sub>Forward</sub>)/PCE<sub>Reverse</sub>] values for the control, TFBA-, TFB-, and PTF-modified devices were 8.26%, 4.13%, 2.93%, and 1.64%, respectively (see Table S2). These indicate that the PTF-modified device exhibited the best performance with the smallest hysteresis, which was attributed to the stronger anchoring interactions of PTF, leading to more effective trap defect passivation. Figure 4c shows the EQE of the control and the PTF-modified PSCs device. The integrated current density of the PTF-modified device was 25.70 mA/cm<sup>2</sup>, higher than that of 25.24 mA/cm<sup>2</sup> for the control device, which was consistent with the current density from the J–V curves. Figure 4d and S3 show the statistical data on the photovoltaic parameters (PCE, V<sub>oc</sub>, J<sub>sc</sub>, and FF) of devices with different modifiers and modifications. Specifically, the V<sub>oc</sub> of PTF-modified

devices increased significantly, meaning less V<sub>oc</sub> loss, thus resulting in the highest PCE.

To further specifically verify the positive effect of PTF modification on device performance and its positive effect on suppressing defects and promoting interface charge transfer for reducing V<sub>oc</sub> loss, we conducted a series of electrical performance tests. Figure S4 presents the Mott–Schottky (M–S) plot of the PSCs at 10 kHz. At the perovskite/ETL interface, the built-in potential (V<sub>bi</sub>) of the device using PTF was increased from 0.93 V to 0.97 V, indicating a stronger driving force for the separation of photogenerated carriers. The electrochemical impedance spectroscopy (EIS) results (see Fig. S5) showed that the interfacial charge recombination resistance significantly increases after PTF modification, which may explain the reduced V<sub>oc</sub> loss and the suppression of non-radiative recombination. Figure S6 shows the typical dark current–voltage (I–V) curves of the hole-transporting-only devices. The trap-filled limit voltage (V<sub>TFL</sub>) of 0.50 V for the PTF-modified device was lower than that of 0.82 V for the control device, indicating a lower defect density and higher film quality. The lower response to V<sub>TFL</sub> and defect state results are also reflected in electron-transporting-only devices (see Fig. S7). From transient photocurrent/photo-voltage decay (TPC/TPV) tests, the carrier transit time (τ<sub>tr</sub>) calculated from the TPC curve of the PTF-modified device was 1.70 µs, shorter than the 4.35 µs of the control device. This indicates improved charge extraction capability due to the enhanced energy band alignment and reduced interfacial energy barrier (see Fig. 4e). The carrier recombination lifetime (τ<sub>rec</sub>) derived from the TPV curve indicates that PTF treatment could induce the τ<sub>rec</sub> increase from 15.16 µs to 53.9 µs, indicating a significant suppression of non-radiative recombination (see Fig. 4f).

To verify the positive impact of PTF on surface trap defect passivation and photogenerated current uniformity in PSCs, we conducted light beam-induced current (LBIC) measurements using a 520-nm light beam to obtain the spatial distribution of the photoresponse. The control PSCs showed significant heterogeneity in photoresponse, while the PTF-modified PSCs showed more uniformity and higher photocurrent intensity (see Fig. 4g, h). After storing the unencapsulated devices under light conditions and outdoor environments for 30 days, the LBIC results indicated that PTF modification could suppress ion migration within the perovskite, hindering the chemical reaction between I<sup>-</sup> and Ag for preventing the common Ag electrode corrosion effects. This suggested that PTF-based surface passivation could reduce defect density and inhibit the migration of halide ions, improving uniformity and photogenerated current output ability. In addition, we evaluated the long-term stability of unsealed control and PTF-modified PSCs by storing the device in ambient conditions (at 35 ± 5% relative humidity (RH) and a temperature of 25 ± 5 °C). It could be seen
<figure><img src="image_9.png" /><figcaption>**Fig. 4** **a** Structure diagram of inverted perovskite solar cell device with modification layer added. **b** Best-performing J-V curves of the best-performing control, TFBA, TFB, and PTF-modified 1.53 eV perovskite-based PSC devices in reverse and forward scan mode. **c** EQE curves for the encapsulated with control, TFBA, TFB, and PTF. **d** Statistical distribution diagram of the PCE and V<sub>oc</sub> parameters of the control and PTF-modified devices employing conventional bandgap</figcaption></figure>

1.53 eV perovskite. **e** TPC and **f** TPV curves for the control and PTF-modified devices. LBIC images of the **g** control, and **h** PTF-modified perovskite films (the top row is fresh perovskite films and the bottom row is perovskite films after aging for 30 days at room temperature under RH of 60±10%). **i** Long-term stability test of the devices with and without PTF aging for 1 600 h through exposure to relative humidity (RH) of 35±5% in the dark

<figure><img src="image_10.png" /></figure>
that after 1 500 h of aging, more than 85% of the original PCE could still be maintained during the PTF modification (see Fig. 4i). The thermal stability test at 85 °C (see Fig. S8) revealed that the PTF-modified PSCs could maintain 70% of their initial efficiency after nearly 100 h of aging, while the control PSCs could only maintain 40% of their initial values.

## 3 Conclusion

In conclusion, we developed three rationally designed passivation molecules—TFBA, TFB, and PTF—to target Pb–I antisite defects and optimize the interface of PSCs. These molecules demonstrated varying passivation efficiencies due to their same type of active site (carbonyl, trifluoromethyl, and benzene intermediates) but distinct functional groups and spatial configurations. Among them, PTF exhibited the strongest passivation performance, effectively coordinating its carboxyl and fluorine groups with undercoordinated Pb²⁺ ions. This interaction not only minimizes interfacial energy loss by trap defects passivation and bandgap alignment modulation but also reduces ion migration. PTF-modified devices achieved a PCE exceeding 25%, with improved energy level alignment, enhanced charge transport, and superior long-term stability, retaining over 85% of initial efficiency after 1 500 h of aging. These findings provide a clear pathway for optimizing molecular passivators to enhance both the efficiency and stability of PSCs.

# 4 Experimental section

## 4.1 Materials

Formamidinium iodide (FAI, 99.5%), cesium iodide (CsI, ≥ 99.9%), and methylammonium iodide (MAI, ≥ 99.9%) were purchased from Shanghai Macklin Biochemical Co., Ltd (Shanghai, China). Lead iodide (PbI₂, 99.99%) and lead chloride (PbCl₂, 99.5%) were obtained from Xi’an Polight Optoelectronics Technology Co., Ltd (Xi’an, China). Methylammonium chloride (MACl, ≥ 99.5%) was purchased from Greatcell Solar Materials (New South Wales, Australia). NiOₓ was synthesized in the laboratory using a simple organic solvent method. 4-(Trifluoromethyl) benzoic anhydride and 4-(trifluoromethyl)benzoic acid ethyl ester were purchased from Energy Chemical Co., Ltd (Xi’an, China). 4-(Trifluoromethyl)benzoic acid was purchased from Shanghai Meryer Biochemical Technology Co., Ltd (Shanghai, China). Me-4PACz was purchased from TCI (Shanghai, China). N,N-Dimethylformamide (DMF, ≥ 99.9%) and dimethyl sulfoxide (DMSO, ≥ 99.8%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd (Shanghai, China). BCP was purchased from Youxuan

Technology Co., Ltd (Liaoning, China). C60 was purchased from Luminescence Technology Corp. (Shanghai, China). Nickel(II) nitrate hexahydrate (Ni(NO₃)₂·6H₂O, 99.999%) was purchased from Aladdin (Shanghai, China) and used for the synthesis of NiOₓ nanoparticles for inverted PSCs.

## 4.2 Device fabrication

First, the laser-etched ITO glass substrates were sequentially cleaned with detergent solution, deionized water, and anhydrous ethanol for 30 min each. Next, the substrates were further cleaned by O₃ treatment for 20 min. Then, 15 mg of NiOₓ powder was dissolved in 1 mL of deionized water, followed by sealing and ultrasonic treatment for about 8 min. The NiOₓ precursor was then spin-coated onto the ITO substrates at 2 000 rpm for 30 s, followed by annealing at 150 °C for 10 min. After annealing, the ITO/NiOₓ substrate was quickly transferred into an N₂-filled glovebox for subsequent preparation. Me-4PACz (0.5 mg/mL predissolved in isopropyl alcohol (IPA) and ultrasonic bath for 10 min) solution was spin-coated onto the ITO/NiOₓ layer at 3 000 rpm for 30 s, followed by annealing at 100 °C for 10 min. The stoichiometric Cs₀.₀₅MA₀.₀₅FA₀.₉PbI₃ precursor solution was prepared by dissolving 20.784 mg of CsI, 247.68 mg of FAI, 12.72 mg of MAI, 15 mg of MACl, 11.124 mg of PbCl₂, and 785.55 mg of PbI₂ in a mixed solvent of DMF/DMSO (4:1, by volume). For the 1.53 eV Cs₀.₀₅MA₀.₀₅FA₀.₉PbI₃ film crystallization, the perovskite films were deposited by spin-coating the perovskite precursor solution on glass/ITO/NiOₓ/Me-4PACZ substrate at 1 000 rpm for 10 s and 5 000 rpm for 30 s. The wet perovskite film was quickly put into a sample chamber connected to vacuum-pumping instrumentation (internal space 12 cm × 12 cm × 2.1 cm). By opening the valve connecting the specimen chamber to the pump system, the perovskite film was immediately exposed to low pressure maintained at 10 Pa for 40 s, followed by full pressurization by admitting ambient air into the specimen chamber. Subsequently, the perovskite film was annealed at 100 °C for 15 min in the air (RH = 30 ± 10%, temperature = 25 ± 5 °C) for full crystallization. TFBA (0.4 mg/mL), TFB (15 µL/mL), and PTF (0.5 mg/mL) were all dissolved in IPA and spin-coated at 3 000 rpm for 30 s, followed by annealing at 100 °C for 5 min. Subsequently, 80 nm of C60 and 5 nm of BCP were evaporated onto the perovskite film, followed by the evaporation of 500 nm of Ag as the back electrode. This completed the fabrication of the entire device.

## 4.3 Measurements and characterization

The J–V characterizations were measured by a Keithley 2400 source measurement unit under simulated AM 1.5 irradiation (100 mW/cm²) with a standard xenon-lamp-based solar simulator (7ISO503A, SOFN Instruments).
These measurements were conducted either via a forward scan, ranging from -0.1 V to 1.4 V, or a reverse scan, from 1.4 V down to -0.1 V. The EQE was determined using an EQE measurement system from Enli Tech, Taiwan, China. All assessments were performed at room temperature in an ambient atmosphere, and the solar cells were not encapsulated during these measurements. GIWAXS images were collected on BL1W1A at the Beijing Synchrotron Radiation Facility (BSRF) (λ = 0.154 nm). The incidence angle was 0.16° and the exposure time was 100 s. XRD was measured on Rigaku SmartLab powder X-ray diffractometer using Cu Kα radiation. The measuring power was 2 kW, the scanning angle was 10°-55°, and the scanning speed was 8° per minute. The Fourier transform infrared spectroscopy (FTIR) spectra were measured using the reflectance method by FTIR-850 of Gangdong Tianjin. XPS and UPS spectra were collected through Thermo ESCALAB XI+. Agilent 5500 scanning probe microscopy was utilized for AFM topography and KPFM in tapping mode, whereas CS-AFM was in contact mode with 1 V applied bias. The PL and TRPL were measured by the Horiba Fluorolog-3 Time-Correlated Single Photon Counting system with an excitation wavelength at 470 nm. EIS measurement was performed in the dark by AMETEK VersaSTAT 3F at a frequency from 1 Hz to 1 MHz. Mott-Schottky measurement was done by using the same instrument as used in EIS but at a fixed frequency of 1 kHz. The applied bias voltage range was 0 V. TPC/TPV and $t_{rise}/t_{fall}$ were tested by PD-RS of ENLITECH. Taiwan, China. LBIC mapping measurements were tested by the DSR500-LBIC instrument of Zolix, Beijing, and LSD4 of ENLITECH.

**Supplementary Information** The online version contains supplementary material available at https://doi.org/10.1007/s44275-025-00026-3.

**Authors' contributions** Jike Ding designed and characterized TFBA, TFB, and PTF additives and their modified perovskite films. Zuolin Zhang and Mengjia Li performed the device fabrication and characterization of PSCs. Rundong Wan and Thierry Pauporte did the theoretical simulations. Taoran Geng, Hongjian Chen, and Cong Chen wrote the paper. Jiangzhao Chen and Cong Chen supervised the research performed in this work, revised the manuscript, and approved the final version.

**Funding** This work was supported by the National Natural Science Foundation of China (U21A2076, 62274018, 52462031), The S&T Program of Hebei (24464401D), The Central Guidance on Local Science and Technology Development Fund of Hebei Province (226Z4305G), Hebei Province Higher Education Science and Technology Research Project (JZX2024030), Shijiazhuang Basic Research Project at Hebei-based Universities (241790847A), and The Natural Science Foundation of Hebei Province (E2024202086, E2024202300).

**Data availability** The data that support the findings of this study are available from the corresponding author upon reasonable request.

## Declarations

**Ethics approval and consent to participate** Not applicable.

**Competing interests** The authors declare no conflict of interest.

**Consent for publication** All authors have read and approved the final manuscript and consent to its publication in *Moore and More*.

**Open Access** This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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**Taoran Geng** received her bachelor of Engineering degree from North China University of Water Resources and Electric Power in June 2019. She is currently a master's student at the School of Materials Science and Engineering, Hebei University of Technology, under the supervision of Professors Hongjian Chen and Cong Chen. Her research focuses on perovskite solar cells.

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**Jike Ding** received his BE from Tianjin University of Technology in June 2020. He is currently a master's student at the School of Materials Science and Engineering at Hebei University of Technology, under the supervision of Professor Cong Chen. His research focuses on perovskite solar cells.

<figure><img src="image_14.png" /></figure>

**Zuolin Zhang** received a bachelor's degree in engineering from Hebei University of Technology in June 2021, and is currently a doctoral student in the School of Materials and Engineering of Hebei University of Technology, conducting research under the guidance of Professor Chen Cong. His research interests are perovskite solar cells.

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**Mengjia Li** received her bachelor's degree in engineering from Hebei University of Technology in June 2020. She is currently a doctoral student in the combined master's and Ph.D. program at the School of Materials Science and Engineering at Hebei University of Technology, conducting research under the supervision of Professor Cong Chen. Her research focuses on the failure mechanisms and stability of perovskite solar cells.

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**Hongjian Chen** is currently a professor at Hebei University of Technology. He obtained his Ph.D. from Hebei University of Technology in 2010. His research focuses on crystal growth and application research.

<figure><img src="image_17.png" /></figure>

**Thierry Pauporté** is currently a professor at Paris Sciences et Lettres University (PSL University) and holds a Ph.D. in Physical Chemistry from the University of Montpellier II in France. His research focuses include semiconductor physics and chemistry, as well as functionalization of material surfaces.

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**Rundong Wan** is currently an associate professor at Kunming University of Science and Technology. He received his Ph.D. from the University of Maryland, USA, in May 2006, and his research focuses on first-principles calculations of thermoelectric materials.

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**Jiangzhao Chen** is a professor at College of Optoelectronic Engineering in Chongqing University. He received Ph.D. from Huazhong University of Science and Technology and worked as a postdoc at Sungkyunkwan University and at the University of Hong Kong, respectively. His work focuses on perovskite solar cells.

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**Cong Chen** is currently an professor at Hebei University of Technology. He received his Ph.D. from Jilin University in June 2019. His research focuses on solar cells and NIR photodetectors.

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