Dopant‐Free Hole Transport Materials Afford Efficient and Stable Inorganic Perovskite Solar Cells and Modules

Abstract The emerging CsPbI3 perovskites are highly efficient and thermally stable materials for wide‐band gap perovskite solar cells (PSCs), but the doped hole transport materials (HTMs) accelerate the undesirable phase transition of CsPbI3 in ambient. Herein, a dopant‐free D‐π‐A type HTM named CI‐TTIN‐2F has been developed which overcomes this problem. The suitable optoelectronic properties and energy‐level alignment endow CI‐TTIN‐2F with excellent charge collection properties. Moreover, CI‐TTIN‐2F provides multisite defect‐healing effects on the defective sites of CsPbI3 surface. Inorganic CsPbI3 PSCs with CI‐TTIN‐2F HTM feature high efficiencies up to 15.9 %, along with 86 % efficiency retention after 1000 h under ambient conditions. Inorganic perovskite solar modules were also fabricated that exhibiting an efficiency of 11.0 % with a record area of 27 cm2. This work confirms that using efficient dopant‐free HTMs is an attractive strategy to stabilize inorganic PSCs for their future scale‐up.


Introduction
Hybrid organic-inorganic perovskite solar cells (PSCs) have demonstrated remarkable progress in power conversion efficiencies (PCEs) from 3.8 %t o2 5.5 %i nt he past several years,s howing their great potential in next-generation lowcost photovoltaic technology. [1] However,t he poor thermal stability of hybrid organic-inorganic perovskite materials hinders their large-scale commercialization. [2] Thus,asignifi-cant part of the research focus has been shifted to the allinorganic perovskite structures without volatile organic components. [3] Among the various inorganic monovalent cations,C s + is expected to be the most feasible candidate to substitute the organic cations for two reasons. [4] Thef irst relates to its larger size,w hich satisfies the geometrical constraints of the perovskite structure to establish the continuous array of corner-sharing PbI 6 octahedra. [5] The second arises from the superb thermal stability of CsPbX 3 (X = Cl, Br, and I) materials which may be compositionally stable even at temperatures exceeding 400 8 8C. [6] So far, the efficiencies of all-inorganic Pb-halide PSCs have exceeded 20 %i na nn -i-p structure,w hich was achieved by the tetragonal (b)C sPbI 3 perovskite with an ideal band gap of 1.68 eV for photovoltaic application. [7] Nevertheless,t he imperfect Goldschmidt tolerance factor of black phase CsPbI 3 determines that their PbI 6 octahedra tends to rotate when catalyzed by H 2 O, which induces ar apid phase transition to the non-photovoltaic yellow d phase. [8] Several strategies were reported to address this stability issue including surface energy tuning, [5,9] additive engineering, [10] and interfacial passivation. [11] However,the implementation of these strategies for improving stability is limited due to the potential impact on device performance.F or instance, the amount of the additive is normally low in order to maintain crystallinity and charge mobility of the perovskite film. [12] Similarly,the thickness of the surface passivation layer must be afew nanometers to maintain charge extraction from the active layers to the charge transport layers. [13] Fort hese reasons,highly hydrophobic hole transport materials (HTMs) have received attention, as they have the potential to block the moisture-driven phase transition of black phase CsPbI 3 . [14] At present, state-of-the-art CsPbI 3 PSCs still use 2,2',7,7'tetrakis(N,N-di-p-methoxyphenyl-amino)-9,9'-spi-robifluorene (spiro-OMeTAD) doped with lithium bis(trifluoromethane)sulfonamide (LiTFSI), cobalt complex and 4-tert-butyl pyridine (TBP) additives as the HTM. [7b, 15] However,w e observed very fast phase transitions ( Figure S19) in the black phase CsPbI 3 films covered with standard doped spiro-OMeTAD layers,w ith these transitions being even faster than that of bare CsPbI 3 films under the same conditions. Hence,t he hygroscopic nature of the dopants eliminates the advantage of the hydrophobicity of the upper hole transport layers and significantly accelerates the phase transition of CsPbI 3 leading to device degradation. [16] Therefore,d eveloping dopant-free,efficient, and stable HTMs is highly desirable and could lead to practical applications of inorganic perovskites in PSCs.
Herein, we described the design and synthesis of adopantfree D-p-A type HTM, namely CI-TTIN-2F,e mploying at riazatruxene (TAT)a st he electron-rich donor,a lkylated terthiophene as p-bridges,and afluorinated Lewis base as the electron-deficient acceptor.B enefiting from intramolecular charge transfer (ICT) and strong dipolar intermolecular interactions,C I-TTIN-2F shows excellent optoelectronic properties,i deal energy-level alignment, and good charge collection properties.I na ddition, joint experimental and theoretical studies suggest that CI-TTIN-2F provides multisite defect-healing effects on the surface of the CsPbI 3 films due to the presence of various heteroatoms (N,O ,S ,F)inthe HTM structure,w hich effectively reduces the trap densities and charge recombination at the interface.A sadopant-free HTM for the all-inorganic CsPbI 3 PSCs,CI-TTIN-2F impressively delivers high PCEs of 15.9 %o ns mall-area cells and 11.0 %onmodules with arecord area of 27 cm 2 .Furthermore, the device employing CI-TTIN-2F maintains over 86 %ofits initial performance for 1000 ha fter storage in ambient conditions. Figure 1a depicts the chemical structure of CI-TTIN-2F HTMs.T he synthetic routes and the synthetic details are given in the Supplemental Information (Figures S1-S3). A planar nitrogen-containing triazatruxene (TAT)c ore with alkyl chains was employed as the donor (D) due to its excellent charge transporting and strong p-p stacking ability. [17] Thea lkylated terthiophene conjugated arms,3 ,3''dihexyl-2,2':5',2''-terthiophene,w ere modulated as p-bridge to increase hole-mobility properties of the molecule by increasing the double-bond character. [18] Astrong Lewis base electron-withdrawing acceptor (A) unit, 2-(5,6-difluoro-3oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IN-2F), was selected based on D-p-A type architecture to decrease the LUMO levels without causing strong steric hindrance, enhance inter/intramolecular non-covalent interactions,a nd increase hydrophobicity,l eading to long-term stability.T he expected structure of CI-TTIN-2F was confirmed by MAL-DI-TOF mass spectrometry ( Figure S4). To evaluate the thermal properties of CI-TTIN-2F thermogravimetric analysis (TGA) was carried out under an itrogen atmosphere ( Figure S5). Thed ecomposition temperature (T dec )c orresponding to aw eight loss of 5% occurs above 300 8 8C, indicating that CI-TTIN-2F has sufficient thermal stability for application as aHTM in PSCs.Moreover,CI-TTIN-2F is soluble in tetrachloroethane,a nd reasonably soluble in tetrahydrofuran and dichloromethane,a llowing solution processing.

Results and Discussion
Theo ptical properties of CI-TTIN-2F were investigated by ultraviolet-visible (UV/Vis) spectroscopy in the solid state and in tetrachloroethane solution (Figure 1b). TheU V-vis spectra of the CI-TTIN-2F film and solution show multimodal absorption ( Figure S6). Absorption bands were observed between 350 and 500 nm, which may be attributed to the localized aromatic p-p*t ransition of the D-p-A structure. More importantly,a na dditional NIR absorption peak centered at around 660 nm indicates ultra-strong intermolecular charge transfer from the TATelectron-donating unit to the IN-2F electron-withdrawing group.Note that the position of the ICT band is slightly red-shifted as the solution transitions to the solid-state,w hich is characteristic of many organic semiconductors. [19] Theo ptical energy band gap (E g ) estimated from the onset of the absorption peak is determined to be 1.52 eV for CI-TTIN-2F,w hich would increase the intrinsic carrier concentration through the thermal population in the conduction band.
To investigate the highest occupied molecular orbital (HOMO) energy level (E HOMO )ofCI-TTIN-2F,electrochemical cyclic voltammetry (CV) was first performed with as tandard three-electrode configuration ( Figure S7). The material was tested in tetrahydrofuran containing 0.1 M n-Bu 4 NPF 6 as as upporting electrolyte,a nd the oxidation potential was calibrated against an internal ferrocene standard. The E HOMO value was calculated as À5.37 eV vs.vacuum for CI-TTIN-2F.T he HOMO level is well aligned with the valence band energy level of the CsPbI 3 inorganic perovskite so that the photogenerated charge carriers should be efficiently transferred at the interface. [20] Thelowest unoccupied molecular orbital (LUMO) energy levels were calculated to be À3.85 eV by subtracting the optical band gap and HOMO energy level. These results are consistent with the trend estimated from density functional theory (DFT) calculations (Table S1 and S2). Them olecular structures were optimized by using PBE-D3 density functional. Thel ocalization and energies of the frontier molecular levels of CI-TTIN-2F for the HOMO are delocalized primarily in the TATc ore and spread along the entire molecule,while LUMO are localized in the acceptor moiety and p-bridge of the HTM (Figure 1c). Figure 1d shows the schematic of the energy band diagram. Thee nergy bands of the CsPbI 3 perovskite were characterized by ultraviolet photoelectron spectroscopy (UPS) and UV-vis spectroscopy as shown in Figure S8. Theenergy level alignment implies that the fluorinated IN-2F acceptor unit with stronger electron-withdrawing properties endows CI-TTIN-2F with much deeper HOMO energy levels by 0.40 eV compared to spiro-OMeTAD.T he lower HOMO of CI-TTIN-2F is expected to ensure more efficient interfacial holetransport kinetics and improve the open-circuit voltage (V OC ) for CsPbI 3 PSCs. [21] Thes pace-charge limited current (SCLC) measurements were carried out on the hole-only devices to evaluate the charge transport properties of CI-TTIN-2F,a nd the hole mobilities were extracted following the Mott-Gurney Law ( Figure 1e). Encouragingly,with the D-p-A molecular structure,C I-TTIN-2F exhibits high hole mobility of 3.7 10 À4 cm 2 V À1 s À1 ,s ignificantly higher than that of spiro-OMe-TAD( 6.1 10 À5 cm 2 V À1 s À1 ), attributed to the higher degree of conjugation and better intermolecular interactions. [22] Grazing incidence wide-angle X-ray scattering (GIWAXS) was performed to investigate the molecular organization in the HTM films (Figure 1f). Thep ole plots of the azimuth angle integrated around q z = 3.5 À1 ( Figure S9) indicate that both CI-TTIN-2F and spiro-OMeTAD possess multiple orientations in the films.B esides the face-on orientation, CI-TTIN-2F exhibits edge-on stacking that favor charge transport. [17] To investigate the potential interactions occurring be-  Figure S11). This is partially due to the face-on configuration of CI-TTIN-2F CN groups within 2FIN which coordinate with the perovskite surface,a sm alononitrile unit can rotate.Consequently,coordination of the CN group with the surface rotates the conjugated 5,6-difluoro-3-oxo-2,3dihydro-1H-inden-1-ylidene moiety having aq uasi-planar geometry (Figures 2a), lifting the Fatoms and thus elongating the Pb-F distances.H owever,t he weak Pb-F contacts (Figure S12) contribute to more intimate interactions between the HTM and the perovskite surface.i ii)T he lone pairs of electrons on sulfur atoms of the p-bridges interact with the Pb 2+ cations of the surface,w hich are similar to previously reported oligothiophene HTMs. [23] ThePb-S distances around 3.7 are below the sum of van der Waals radii of Pb and S, evidencing coordination interactions.i v) Thea verage Pb-O distances in the stabilized molecular conformation are about 3.0-3.5 ,which is below or close to the sum of van-der-Waals radii of the interacting atoms.T he average distances of the shortest contacts I-X (X = O, N, S, F) are longer, being about 4 .Intheface-on configuration the hexyl units also tend to orient along the perovskite surface,w hich allows the sitespecific non-covalent Pb-X interactions to be maximized, since the corresponding parts of HTM can sufficiently approach the surface.S ome hexyl units are unable to orient parallel to the surface due to the steric hindrance produced by other parts of CI-TTIN-2F (Figure 2a), and sometimes the hexyl chains provide steric hindrance.
To elucidate the impact of CI-TTIN-2F on the electronic structure of the interface,arepresentative snapshot during the MD trajectory was selected to simulate the electronic structure using PBE0 density functional (Figure 2b,c ). The perovskite surface was represented by PbI 2 -terminated slab, in which each Pb 2+ ion can be considered as unsaturated, representing ad efect. In the absence of CI-TTIN-2F on the perovskite surface,P b-centered trap-like states were observed at the bottom of the conduction band of the perovskite ( Figure 2b). Interestingly,u pon coverage of the perovskite with CI-TTIN-2F,t hese states disappear,w ith the contribution of the Pb 2+ ions being "merged" with the continuous manifold of states at the bottom of the conduction band ( Figure 2c). Moreover,t he empty CI-TTIN-2F-centered states are situated below the conduction band manifold ( Figure S13). Consequently,a ne lectron from the bottom of the perovskite conduction band at the interface can migrate on the CI-TTIN-2F instead of recombining with the holes. Moreover,t he participation of CI-TTIN-2F orbitals in the formation of the bottom of the conduction band favors electron delocalization over the perovskite/HTM interface, which in turn facilitates electron migration.
X-ray photoelectron spectroscopy (XPS) was carried out on the CsPbI 3 and CsPbI 3 /CI-TTIN-2F films to verify the calculations.H igh-resolution Pb 4f spectra are shown in Figure 2d.A part from the two main Pb 4f 7/2 and Pb 4f 5/2 peaks,t wo additional peaks around 136.9 and 141.8 eV were observed in the CsPbI 3 film attributed to the presence of the metallic Pb. [24] Thesubstantial metallic Pb species indicate the existence of iodide vacancies or under coordinated Pb 2+ defects,w hich are likely to behave as non-radiative carrier recombination centers and impede the solar cell performance. After depositing the CI-TTIN-2F HTM, the Pb 4f peaks shift to lower binding energies,and the two metallic Pb peaks are greatly restrained, demonstrating the strong interactions and the effective passivation of the CI-TTIN-2F HTM on the perovskite surface,i nl ine with the MD and PDOS calculations.T he influence of CI-TTIN-2F on the trap density of states of the CsPbI 3 film was further investigated by spacecharge limited current (SCLC) characterization (Figure 2e, f). [25] Thed ark current density-voltage curves show three representative regions consisting of al inear ohmic, at rapfilled, and at rap-free SCLC region. Thet rap-filled limit voltage (V TFL )i sr educed to 0.88 Vf rom 1.27 V, and the corresponding trap density of states decrease to 3.04 10 15 from 4.38 10 15 cm À3 after depositing the CI-TTIN-2F HTM. These results confirm that CI-TTIN-2F can efficiently passivate the under coordinated Pb 2+ defects on the CsPbI 3 perovskite surface through the interactions identified by the calculations.
Since charge extraction properties are crucial for HTMs, we examined the charge-carrier dynamics in pristine CsPbI 3 and CsPbI 3 /HTM films using steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy.T he pristine CsPbI 3 film exhibits the strongest PL emission centered around 725 nm ( Figure S14). Significant quenching was observed in the presence of the HTM, and CI-TTIN-2F has the lowest PL intensity,s uggesting rapid hole extraction across the interface and asuperior hole extraction ability of CI-TTIN-2F compared to spiro-OMeTAD.T RPL spectroscopy was used to delineate the carrier dynamics quantitatively (Figure 2g). Thep ristine CsPbI 3 film shows al onger lifetime (t 1 = 2.11 ns), which was reduced by the HTM due to the charge extraction. TheC sPbI 3 /CI-TTIN-2F junction presents faster hole transfer (0.69 ns) than the CsPbI 3 /spiro-OMeTAD interface (0.76 ns), most likely due to the deeper valence band maximum of CI-TTIN-2F and the stronger interfacial interactions between the Pb 2+ ion on the perovskite surface and 2FIN units of CI-TTIN-2F compared to spiro-OMeTAD. [26] PL mapping images in Figure 2h,i reveal as imilar trend where the sample with CI-TTIN-2F displays lower integrated intensity than spiro-OMeTAD.I n addition, improved emission homogeneity was achieved by CI-TTIN-2F,w hich might result from the passivation of surface defects and the oriented face-on stacking of the HTM. Figure 3a shows the cross-section SEM image of the complete PSCs with an n-i-p structure comprising FTO/TiO 2 / CsPbI 3 /CI-TTIN-2F/Au, in which the thickness of the CI-TTIN-2F hole transport layer (HTL) was optimized at % 50 nm. Thed etailed fabrication of the devices is described in the Supporting Information, and all the HTMs were employed without any dopant if not otherwise specified. Negligible change in grain sizes and morphologies of CsPbI 3 films is observed after HTL deposition as shown in the surface-section SEM images ( Figure S15). Thebest-performing CI-TTIN-2F-based device shows aPCE of 15.91 %under reverse scan conditions,w ith as hort-circuit photocurrent density (J SC )o f1 8.82 mA cm À2 ,aV OC of 1.10 V, and af ill factor (FF) of 77.50 %, and aPCE of 15.29 %inforward scan condition, with a J SC of 18.82 mA cm À2 ,aV OC of 1.06 V, and an FF of 76.90 % (Figure 3b). Thedevice performance is higher than that of the spiro-OMeTAD-based PSC with an efficiency of 11.44 %u nder reverse scan and 8.68 %i nf orward scan ( Figure S16), reflecting the lower-lying HOMO levels as well as the improved hole mobility and extraction for CI-TTIN-2F HTM. Thet wo devices exhibit similar integrated photocurrent values (Figure S17), and the main difference in efficiency derives from the V OC and FF.T oe xplore the fundamental reasons,a dditional electrical characterization was performed on these devices.Electrochemical impedance spectroscopy (EIS) analysis reveals as maller EIS resistance value for the CI-TTIN-2F-based device relative to the spiro-OMeTAD-based device (Figure 3c), demonstrating its better charge-transfer behavior. [19] Theheterojunction properties at the perovskite/HTM interface were analyzed by capacitancevoltage (C-V)m easurements.T he C À2 -V plots of the CI-TTIN-2F and spiro-OMeTAD-based device are depicted in Figure 3d,following the Mott-Schottky Equation (1): where C is the capacitance, V bi refers to the built-in potential, N D represents the charge density,and V stands for the applied voltage. k B , T, e, e,a nd e 0 are the Boltzmann constant, thermodynamic temperature,e lementary charge,r elative dielectric constant and vacuum permittivity,r espectively. The V bi caused by the carrier diffusion is crucial for charge injection in solar cells,which is estimated to be 1.15 Vfor the CI-TTIN-2F-based device,o utperforming the spiro-OMe-TAD-based device (1.07 V), consistent with the decreased energy level of CI-TTIN-2F (Figure 1b). Therefore,C I-TTIN-2F extends the depleted region and enhances the driving force for carrier injection, which directly contributes to the increased V OC . [27] Moreover,t he larger slope of the Mott-Schottky plot for the CI-TTIN-2F-based device suggests al ower interfacial charge density (3.79 10 16 cm À3 vs.8 .79 10 16 cm À3 )a nd thus improved charge extraction. Theh igher charge accumulation at the perovskite/spiro-OMeTADinterface also explains the larger hysteresis. [28] Thetrap density of states (tDOS) was also deduced from the angular frequencydependent capacitance for the fabricated devices ( Figure 3e). TheC I-TTIN-2F-based device demonstrates reduced trap states compared with the spiro-OMeTAD-based device over the whole defect energy region. This reduction derives from the effective surface passivation of CI-TTIN-2F,w hich is confirmed by the removal of trap states (Figure 2b). Accordingly,trap-assisted recombination is efficiently suppressed, as validated by the smaller ideality factor of 1.57 for the CI-TTIN-2F-based device compared with 1.92 for the spiro-OMeTAD device (Figure 3f). Hence,C I-TTIN-2F gives rise to advantageously accelerated interface charge transfer, diminishes surface defects,a nd suppresses trap-assisted recombination, which reduces energy loss and thus enhances device performance,especially for V OC and FF.
To demonstrate large-scale application of the CI-TTIN-2F HTM, inorganic CsPbI 3 perovskite modules with an active area of 27 cm 2 were fabricated (Figure 3g). Themodules were patterned by the P1, P2, and P3 laser-scribing method (Figure 3h), consisting of nine sub-cells.N otably,t he CsPbI 3 PSC module achieves aP CE of 10.98 %e mploying the CI-TTIN-2F HTM, with a J SC of 1.96 mA cm À2 ,aV OC of 9.36 V, and an FF of 60 %. Thes imilar V OC of each sub-cell with as ingle cell implies the good uniformity of the HTM layer over alarge area. Thereduced J SC and FF can be attributed to the greater series resistance because of the longer carrier transport paths and the device nonuniformities.M oreover, the perovskite solar module with the CI-TTIN-2F HTM shows as teady output PCE of 10.80 %u nder the AM 1.5 G illumination for 250 s, which is consistent with that calculated from J-V scanning ( Figure S18). Thep erformance of the reported inorganic perovskite modules versus device area are summarized in Figure 3i. [29] Thee fficiency of the CI-TTIN-2F-based module is comparable with that of previous reports while showing the largest module area.
Moisture-induced phase transitions of the perovskite film are ac ritical degradation path for all-inorganic PSCs.T o examine the effects of HTL incorporation on the phase stability of perovskite films,w et racked the absorbance evolution of CsPbI 3 films under acontrolled relative humidity (RH) of % 50 %, and photographs of the perovskite films stored for different times are shown in Figure 4a and Figure S19. Remarkably,the CsPbI 3 film covered with doped spiro-OMeTAD is bleached within only 20 min, which is even more rapid than that of the bare CsPbI 3 film (100 min). The degradation onset is significantly retarded to 180 min when the hydrophilic dopants were removed from the spiro-OMeTAD HTL composition. Specially,n oo bvious change in color is observed from the CsPbI 3 film with the CI-TTIN-2F HTM after aging for 480 min. In addition, the long-term phase stability of the films under ambient conditions with an RH of % 20 %w as further investigated by X-ray diffraction (XRD). All the fresh CsPbI 3 films show atypical black phase with two main specific peaks located at 14.68 8 and 29.28 8 which are assigned to (110) and (220) planes,r espectively (Figure 4b). TheC sPbI 3 films with various HTLs behave differently after aging for 360 h ( Figure 4c). Ac haracteristic peak assigned to the d phase at 10.28 8 was observed in the bare CsPbI 3 film after aging. [30] Significantly,t he upper spiro-OMeTAD HTL with and without dopants accelerate and decelerate,r espectively,t he phase transition of the CsPbI 3 perovskite structure to the yellow d phase.T hus,t hese hygroscopic dopants not only eliminate the advantage of hydrophobicity of the upper spiro-OMeTAD layer but also further accelerate the phase transition of the CsPbI 3 films. When coated with the dopant-free CI-TTIN-2F HTL, the CsPbI 3 film remains in the black phase and is almost identical to the fresh film, indicating that CI-TTIN-2F is capable of protecting the metastable perovskite films from moisture penetration. To probe surface property of the HTLs,c ontact angles of water droplets on the CsPbI 3 /HTLs samples were measured (Figure 4d). TheCI-TTIN-2F HTL showed amuch higher contact angle of % 998 8 than those of spiro-OMeTAD with ( % 758 8)and without dopants ( % 888 8), and the improved hydrophobicity can be in part attributed to the introduced fluorinated 1,1-dicyanomethylene-3-indanone acceptor units in the D-p-A structure.
Thes tability of unencapsulated CsPbI 3 PSCs employing different HTMs was monitored in an ambient atmosphere with an RH of % 20 %for 1000 hours.F igure 4e presents the normalized PCEs of the devices as afunction of storage time, and the device performances were periodically measured in ambient air.F or comparison, we also fabricated CsPbI 3 devices using spiro-OMeTAD with conventional dopants and the best-performing device exhibited aP CE of 17.77 % with a J SC of 19.53 mA cm À2 ,aV OC of 1.12 V, and an FF of 78.70 %( Figure S20). However,t he ambient stability monitored under ambient conditions reveals that the doped spiro-OMeTAD-based device suffers asharp drop up to < 10 %of the initial PCE within only 100 hdue to the moisture-sensitive dopants.F urthermore,t he dopant-free spiro-OMeTADbased device retains 66 %o ft he pristine performance after 1000 hours.E ncouragingly,t he CI-TTIN-2F-based device maintains 86 %o fi ts initial PCE after 1000 he xposure.T o further enhance device stability,w ee ncapsulated the CI-TTIN-2F-based device and ac ross-section of the encapsulation Scheme is illustrated in the inset in Figure 4f.S uccessfully,the device displays improved stability,and the efficiency drops by only 5% after storing under acontrolled % 50 %RH for over 1500 h. Moreover,w ee xamined the operational stability of the unencapsulated CI-TTIN-2F-based device under ac onstant one sun illumination (AM1.5G) at 25 8 8Ci n an itrogen atmosphere at the maximum powerpoint (Figure 4g). TheC sPbI 3 PSC with CI-TTIN-2F maintains over 80 %o ft he initial PCE under light soaking for 800 h, demonstrating as uperior photochemical stability based on this new CI-TTIN-2F HTM.

Conclusion
We synthesized anew dopant-free HTM named CI-TTIN-2F with aD -p-A molecular configuration. Thes uitable optoelectronic properties and energy-level alignment endow CI-TTIN-2F with excellent charge collection properties.I n addition, joint experimental and theoretical studies suggest that CI-TTIN-2F has the capacity for multisite passivation effects on defective CsPbI 3 surfaces due to the presence of various heteroatoms.A saresult, all-inorganic CsPbI 3 PSCs with dopant-free CI-TTIN-2F HTM demonstrate ahigh PCE of 15.9 %, along with 86 %e fficiency retention after 1000 hours under ambient conditions.T hese results indicate an excellent compatibility of CI-TTIN-2F with all-inorganic PSCs.N otably,t he largest all-inorganic perovskite solar module was fabricated using the CI-TTIN-2F HTM, and exhibited an efficiency of 11.0 %with an area of 27 cm 2 .T his study provides anew design strategy toward efficient dopantfree HTMs with multisite passivation effects that stabilize allinorganic PSCs to facilitate future scale-up.