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A Mechanistic Insight into the Attachment of Fullerene Derivatives on Crystal Faces of Methyl Ammonium Lead Iodide Based Perovskites Mohammad F.N. Taufique, S.M. Golam Mortuza, and Soumik Banerjee J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b07200 • Publication Date (Web): 07 Sep 2016 Downloaded from http://pubs.acs.org on September 12, 2016

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The Journal of Physical Chemistry

A Mechanistic Insight into the Attachment of Fullerene Derivatives on Crystal Faces of Methyl Ammonium Lead Iodide Based Perovskites M.F.N. Taufique, S.M. Mortuza and Soumik Banerjee1 School of Mechanical and Materials Engineering Washington State University, Pullman, Washington 99164-2920, U.S.A.

1

Corresponding author, Tel: +1 509 3350294, E-mail: [email protected] 1 ACS Paragon Plus Environment


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ABSTRACT Recent studies suggest that electron transport layers (ETLs) comprising [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), employed in planar perovskite solar cells, reduce hysteresis by passivating the deep trap states, thereby underscoring the importance of interfacial structures. To gain physical insights into the PCBM-perovskite interfaces during solution processing, we performed molecular dynamics simulations of PCBMs solvated in chlorobenzene near (110) and (100) perovskite surfaces. Our results indicate strong orientational preferences of deposited PCBMs with the strongest associations between the carbonyl oxygen atom of PCBM and the terminating Pb and H atom of (110) and (100) faces of perovskite respectively. The phenyl moiety shows weak associations with the (100) perovskite surface enabling two-pronged anchoring that might facilitate charge transfer. In-plane ordering of PCBMs on perovskite surfaces indicate that a more densely packed monolayer is formed on the (110) surface compared to that on (100) surface and might lead to more efficient electron transport.

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1. INTRODUCTION Thin film perovskite solar cells (PSCs), especially those based on methyl ammonium lead iodide (CH3NH3PbI3) perovskites, have attracted considerable attention because of their high power conversion efficiencies (PCEs).1-6 Based on device architecture, PSCs are classified into two categories, mesoscopic PSCs and planar PSCs.7,

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Mesoscopic PSCs require high

temperature processing of mesoporous oxides (>450 ºC), which is an impediment in large scale production. On the other hand, planar PSCs, which employ electron transport layers (ETLs) to accept electrons from perovskite and transport them to current collectors, are fabricated at low processing temperatures (< 150 ºC). However, planar PSCs have limitations such as hysteresis and current instabilities, presence of intermediate trap states due to excess halide species and chemical defects and pin holes on the perovskite surfaces,9,

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which do not allow PSCs to

achieve their full potential. For instance, the pin holes and defects on the perovskite surfaces impede charge transfer and hence reduce the PCE. In order to minimize such defects, ETLs that are able to extract electrons from perovskites and carry to electrodes, based on materials such as fullerene derivatives, are deposited on perovskite surfaces using solution processing techniques. Specifically, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) based ETLs are advantageous for efficient charge transfer, since PCBM has favorable band alignment with perovskites.11 A recent study

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has further shown that PCBMs also have the potential to reduce hysteresis by

passivating the deep trap states, since PCBMs form stable bond with Pb-I antisite defects. However, for designing effective ETLs based on PCBMs, it is important to gain fundamental understanding of the charge transfer from perovskites to PCBMs and charge transport through the deposited layer. The charge transfer between perovskites and PCBMs depends on the specific association of



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different atoms of PCBMs with the surface atoms of perovskites. Experimentally probing in to the nature of association of different atoms of PCBMs with perovskites is an expensive and timeconsuming process. Molecular modeling techniques, which have been successfully applied to provide theoretical insights on the nature of molecular interactions and resulting self-assembled structures of nanoparticles on interfaces for various applications,12,

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could be effective in

investigating the PCBM-perovskite interfaces formed during solution processing of ETLs. Specific molecular structures of PCBMs on various perovskite surfaces, essential to gain physical insight into the nature of charge transfer and transport through ETL, have not been modeled. Therefore, the objective of the present study is to model the deposition of solvated PCBMs, mimicking solution-processing conditions, on distinct perovskite surfaces, and analyze the orientation and association of various moieties of PCBMs relative to the perovskite surfaces. The ultimate goal is to comprehensively assess the structural and transport characteristics from the perspective of PCBM deposition and provide insights and speculations on charge transfer from the perovskite to the ETL comprising PCBMs and charge transport through the ETL. 2. METHODOLOGY To achieve the above-mentioned goal, we performed molecular dynamics (MD) simulations of 100 PCBMs dispersed in chlorobenzene (CB) solvent sandwiched between two CH3NH3PbI3 perovskite crystal surfaces. The initial configuration of the simulated system is shown in Figure 1. We chose the (110) and (100) faces of tetragonal CH3NH3PbI3 as model systems since earlier studies have shown that these particular faces promote long charge carrier lifetimes.14 Detailed information of the total number of PCBMs, number of deposited PCBMs and CB molecules in the simulated systems are provided in Table S1 in the Supporting Information. To eliminate biased aggregation and depositions, we kept the distances between centers of mass of each


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PCBM and the surfaces sufficiently large (at least ~1.5 nm) at the initial configuration. The concentration of PCBM stock solution was approximately 0.18 M (~15% mass fraction) in both systems. We performed the simulations at an elevated temperature of 400 K, which is less than the boiling point of CB,15 in order to augment the kinetics of the simulated systems as well as to mimic often-used solvent processing at slightly elevated temperatures.16

Buffer zone 2 nm

Perovskite surface

CB solvent

10 nm

PCBM

2 nm

Perovskite surface

Z Y 10 nm X

Figure 1: Representative snapshot of the configuration simulated with MD is shown. The dimensions of the system in x, y, and z directions are 10 nm, 10 nm and 14 nm, respectively. The solvent-PCBMs are sandwiched between similar perovskite faces, with a buffer solvent layer that separates period images. Molecular structures have been shown intact at the periodic boundaries.



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The standard OPLS-AA (Optimized Potentials for Liquid Simulations - All Atom) force field17 parameters for bonded and non-bonded interactions were used for PCBM and CB, except for the fullerene moiety of PCBM. We employed Girifalco’s18 parameters to describe the nonbonded interactions for the fullerene aromatic carbons, as reported in a previous work on fullerene aggregation.19 We have also employed these parameters for PCBMs in organic solvents in an earlier work.20 However, original OPLS-AA force field lacks the partial charges of atoms of the PCBM molecule in CB. Therefore, we used density functional theory (DFT) to calculate the partial charges of a PCBM in presence of CB using NWChem21 shown in Figure S1 and Table S2 in the Supporting Information. The geometry of the PCBM was first optimized. The partial charges on atoms of PCBM in presence of CB were calculated based on B3LYP theory 22, 23

with a 6-31G (d) basis set.24 To account the solvent effects, we used the Conductor-like 25

Screening Model (COSMO)

in the DFT calculation. The optimized structure of PCBM is

shown in Figure 2. The CB solvent was treated as continuum with a dielectric constant of 5.62.26 We adopted the force fields parameters for perovskite crystals from a recently published work.27

b

c

d

a

Figure 2: Some key atoms, which play important roles during the deposition of PCBMs on


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perovskite surfaces, of a PCBM molecule are highlighted with black circles. The oxygen atom bonded to the carbon atom of the carbonyl group by a double bond is referred as carbonyl oxygen (CO), presented in (a). The methoxy oxygen (MO), the methoxy carbon (MC) and a representative phenyl carbon (PC) atom are presented in (b), (c) and (d), respectively. All MD simulations were performed with the GROMACS software package (v4.6.1).

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Initially we solvated PCBMs with CB molecules and performed equilibration runs of PCBM-CB systems in several steps until the concentration of the systems reached 0.18M. We performed equilibration runs for at least for 100 ps in each of these steps. After creating an equilibrated PCBM-CB system, we performed a separate equilibration run for the overall system, comprising equilibrated solution sandwiched between perovskite surfaces, for 300 ps followed by NVT production run for at least 60 ns. A stochastic velocity rescaling thermostat,29 with relaxation time 1 ps, was used to maintain constant temperature of 400 K. The equations of motion were integrated with a time step of 1 fs. A cutoff distance of 1.5 nm was employed for all non-bonded interactions in the MD simulations. The particle mesh Ewald (PME)

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method was used to

account for the long-range electrostatic interactions. The atoms in the perovskite crystal were tethered with a harmonic potential describing their vibration about a mean position in the crystal structure. While such tethering will not allow for the rotational dynamics, particularly of the organic groups, in the perovskite, we assume that the primary interactions with the terminating groups on the surface will not be significantly influenced by such fast rotational dynamics. 3. RESULTS AND DISCUSSION In an effort to analyze the association and orientation of PCBMs with respect to both (110) and (100) perovskite surfaces, Figures 3 (a) and (c) present the time-averaged number density distributions of the center of mass (COM) and other key atoms of PCBM, shown in Figure 2, that 7 ACS Paragon Plus Environment


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play important roles during their deposition on the perovskite surfaces. The number densities at various distances from the perovskite surfaces, presented in Figure 3, are average values with respect to both surfaces in the simulated system. Figure 3 (a) shows a sharp peak of carbonyl oxygen atoms of PCBMs at a distance of 0.25 nm from the (110) plane, indicative of short range ordering of these atoms near the perovskite surface. Due to the presence of the methoxy carbon atom of the ester moiety near the carbonyl oxygen atom, a weak peak for the carbon atom is also observed at a distance of 0.37 nm. Figure 3 (a) further shows a peak for COM of PCBMs at a distance of 0.89 nm from the (110) surface. However, phenyl carbon does not form a distinctive peak near the surface. Based on the number density distributions, it is evident that the ester moiety of the PCBM faces the (110) plane of perovskite surface, while the fullerene moiety is away from the surface during the deposition. Therefore, the ester moiety possibly plays a significant role in electron hopping from perovskite crystal to deposited PCBMs. Also, the distributions indicate that among all the atoms of PCBM, the carbonyl oxygen atom shows the strongest association with the surface and therefore plays an important role in the deposition of PCBM. However, determining associations between specific surface atoms of perovskite and the carbonyl oxygen requires evaluation of radial distribution functions (RDFs), which are presented later. Similar to that for the (110) surface, the number density distribution for the (100) surface, shown in Figure 3 (c), presents a prominent peak for carbonyl oxygen atoms. However, the peak is less sharp compared to that for the (110) surface, which suggests weaker association of carbonyl oxygen with (100) surface than that with (110) perovskite surface. A peak in the distribution of the phenyl carbon in Figure 3 (c) indicates likelihood of ordering of the phenyl moiety of PCBM near the (100) surface. Hence, both ester and phenyl moieties coordinate with


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the (100) surface during the deposition of PCBMs, and perhaps take part in electron transfer from exposed (100) perovskite surface. Since the fullerene moiety faces away from both (110) and (100) surfaces, a complete monolayer of PCBM with both ester and phenyl moieties anchored to the surface can potentially form a continuous pathway for electron transport. (b)

(a)

Pb

I Pb (c)

(c)

(d)

H

N N

Figure 3: Time averaged number density distributions of COM of PCBM and other atoms of PCBM normal to (a) (110) and (c) (100) plane of perovskite surfaces are shown. Here, D represents the percentage of total number of specific atoms at various distances from the surfaces. The distances are calculated with reference to the terminating Pb and N atoms of the (110) and (100) faces illustrated in (b) and (d) respectively. Only the first prominent peaks of



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COM and key atoms of PCBMs with respect to the perovskite surfaces are shown in order to highlight short range associations. To assess the stability of the PCBMs attached to the surfaces, we evaluated the self-diffusion coefficients of carbonyl oxygen and representative phenyl carbon atoms of deposited PCBMs based on analysis of the last 1000 ps of NVT production run. The self-diffusion coefficients were obtained from the mean squared displacements based on the equation, D = lim→

〈∑ r t − r 0 〉 ,

(1)

where rj t and rj 0 are the positions of atom j at times t and 0 respectively, < > is the ensemble average, and N is the total number of atoms. Corresponding diffusion coefficients for bulk PCBMs not attached to perovskite were calculated to serve as a benchmark and has a value of approximately 2 × 10-10 m2/s. Table 1 shows that the self-diffusion coeffiecients of the atoms of deposited PCBMs in both systems are relatively small in comparison, indicating strong association of the atoms with the surfaces. However, the diffusion coefficient of carbonyl oxygen is almost an order of magnitude lower near the (110) surface compared to that in the proximity of (100) surface indicating a stronger attachment to the former surface. The difference in diffusion coefficients of carbonyl oxygen reflects on full width at half maximum (FWHM) of carbonyl oxygen peaks in Figure 3. The FWHM increases with increasing value of diffusion coefficient from (110) surface to (100) surface. Table 1 shows that the diffusion coefficient of phenyl carbon is three orders of magnitude greater than that of the carbonyl oxygen near (110) surface, which signifies a relatively weak association of phenyl carbon with the surface, as stated earlier. On the other hand, the diffusion coefficient of phenyl carbon is an order of magnitude smaller near the (100) surface compared to that near the (110) surface suggesting stronger association with (100) surface atoms, as seen in Figure 3. Such stable associations have profound implication on charge


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transfer from perovskite to the ETL and is discussed later. Table 1: Calculated values of self- diffusion coefficients of carbonyl oxygen and representative phenyl carbon of deposited PCBMs are provided. Model system Diffusion coefficient (m2/sec) Carbonyl oxygen (110) surface (100) surface

-14

Phenyl carbon 1.42 × 10-11 1.53 × 10-12

8.8 × 10 3.5 ×10-13

While the number density distribution and diffusion coefficient of the key sites of PCBM throw light on the orientation of PCBM as well as the nature of association of the atoms with the overall surfaces, it is important to analyze the coordination of the atoms with the specific atoms on the surfaces that contribute to the direct electron transfer processes at the perovskite-ETL interface. To evaluate such coordination, we determined RDFs of the key atoms of PCBM with respect to the terminal atoms of the perovskite surfaces, where (110) plane is terminated by lead (Pb) and iodine (I) atoms (Figures 4(a) and (b) respectively), and the (100) plane is terminated by hydrogen (H) and nitrogen (N) atoms (Figures 4(c) and (d) respectively). A sharp peak observed at ~ 0.24 nm in the RDF of carbonyl oxygen with respect to Pb, shown in Figure 4 (a), signifies a strong association of the carbonyl oxygen atoms with the Pb atoms of perovskite likely due to the strong Coulombic interactions between the negatively charged oxygen and the positively charged Pb atoms. Since, both I and carbonyl oxygen are negatively charged, a broader and less intense peak at ~0.4 nm in Figure 4 (b) for the RDF of I with resepect to carbonyl oxygen signifies a derivative aspect due to presence of the I atom near to the Pb atom. Figure 4 (a) also shows prominent peaks in the RDFs of Pb-methoxy oxygen and



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Pb-methoxy carbon at ~0.47 nm, which in conjunction with the pronounced peak for Pbcarbonyl oxygen, corroborates our earlier finding that the ester moeity of PCBMs forms strong association and ordering with the (110) perovskite surface thus facilitatiting possible charge transfer. Again, it is evident from the absence of peaks in the RDFs of Pb-phenyl carbon and Iphenyl carbon that the phenyl moeity does not substantially align and coordinate with the (110) surface.

(a)

(c)

(b)

(d)

Figure 4: RDFs of some key atoms, shown in Figure 2, of PCBM with (a) Pb and (b) I atoms of (110) perovskite surface, and (c) H and (d) N atoms of (100) perovskite surface are presented.


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In the case of the (100) perovskite surface, sharp peaks are observed in the RDFs of carbonyl oxygen with respect to H and N atoms, which indicate coordination of the carbonyl oxygen atoms with the atoms on the surface. However, the greater peak height in the RDF of H-carbonyl oxygen compared to that of electron accepting N with respect to the carbonyl oxygen indicates a much stronger association of carbonyl oxygen atoms with the H atoms than with the N atoms. Since both N and carbonyl oxygen atoms are negatively charged, the derivative peak in the RDF of N-carbonyl oxygen is likely due to the presence of N atoms near the H atoms on the crystal surface. The RDF peak further suggests that PCBMs deposit on the (100) surface due to the attractive electrostatic forces between the carbonyl oxygen of PCBMs and the H atoms. However, the relatively diminished peaks in the RDF for H-carbonyl oxygen compared to that for Pb-carbonyl oxygen in (110) face, shown in Figure 4 (a), signifies that the association of the carbonyl oxygen atoms is relatively weaker with the (100) face. Comparatively broad peaks are seen in the RDFs of methoxy oxygen and methoxy carbon with respect to H atoms in Figure 4 (c). Hence, although the ester moeity of PCBM coordinates with (100) surface, the extent of this coordination is weaker compared to that with (110) surface. However, while no association of phenyl group of PCBMs with the (110) plane is observed, as discussed earlier, peaks in the RDFs of phenyl carbon with H and N atoms indicate association of phenyl moeity with the (100) surface, as evident from Figures 3 (c) and (d). The N atom, a strong electron acceptor, is bonded with three hydrogen atoms. As a result, N atoms, surrounded by the electron clouds, attract the positively charged phenyl carbon atoms, as evident from the Nphenyl carbon RDF. However, the corresponding peaks in the RDFs are not well defined and therefore indicate that such coordinations are not very strong. Based on the structural association of deposited PCBMs with the atoms on (100) perovskite surface, although it is highly likely that



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both ester and phenyl moieties take part in electron tranfer, the effect of phenyl moiety is probably less significant compared to that of the ester moiety. Overall, the RDFs indicate strong association of carbonyl oxygen with the Pb and H atoms that play important role in the deposition of PCBM on (110) and (100) surfaces, respectively. However, the coordinations of the ester and phenyl moieties with perovskite depends on the specific nature of the terminating planes of perovskite. An estimate of the free energies for deposition of PCBM on both surfaces, from a simplistic analysis of probabilities of success of PCBMs that attempt deposition, is presented in Supporting Information. The estimated ∆G values are nearly identical for both surfaces, which is likely due to a balance of stronger interactions between carbonyl oxygen and Pb in case of (110) surface with the multiple, albeit weaker, interactions between the phenolic and carbonyl oxygen of PCBM with the (100) face. The device performance of PSCs is dependent on the extent of connected pathways available for the transport of electrons through the deposited PCBMs,31 which can be qualitatively estimated from type of in-plane ordering of deposited PCBMs indicative of the compactness of the solid ETL.31 Therefore, we evaluated the time averaged in-plane distance distribution of the carbonyl oxygen atoms and COM of PCBMs on (110) and (100) perovskite surfaces shown in Figure 5.


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(a)

(e)

(b)

Type A

Type B

(c)

(d) Type C

Figure 5: Time-averaged in-plane distance distributions for (a) carbonyl oxygen on (110) surface, (b) COM of PCBM on (110) surface, (c) carbonyl oxygen on (100) surface, (d) COM of PCBM on (100) surface and (e) in-plane ordering of deposited PCBMs are shown. Here, N represents the percentage of total number of deposited PCBMs within specific distances from each other. By analyzing the in-plane distance distribution plots in Figure 5 (a) – (d) and comparing with the in-plane inter-carbonyl oxygen distances seen in simplified graphical illustrations in Figures S2 and S3 of Supporting Information, we deduce the prevalence of three distinct types of inplane ordering of deposited PCBMs, as presented in Figure 5 (e). These deductions are qualitatively corroborated by observations of these structures in the MD snapshots. Henceforth, we will refer to these structures as “Type A ordering”, “Type B ordering” and “Type C ordering” for the sake of convenience. In “Type A ordering”, the carbonyl oxygen atoms of neighboring deposited PCBMs face opposite sides of the fullerene moiety and are relatively distant, while in 15 ACS Paragon Plus Environment


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“Type B ordering” an imaginary vector joining the carbonyl oxygen atoms and COM of PCBMs would be parallel for neighboring PCBMs. In “Type C ordering”, the two carbonyl oxygen atoms of neighboring PCBMs point towards each other. In the following discussions, we interpret the distance distribution plots with reference to the above-described distinct orderings of deposited PCBMs and present a hypothesis for the effectiveness of charge transport along the deposited layer. In case of the (110) surface, the peak position at 1.18 nm in Figure 5 (a) indicates that distance between two carbonyl oxygen atoms correspond to that between Pb lattice points on the (110) surface, presented in Figure S2. The corresponding distance between COM of PCBMs is 0.9 nm, as seen in Figure 5 (b). On the other hand, for the (100) surface, peak position at 1.28 nm in Figure 5 (c) corresponds to two carbonyl oxygen atoms of PCBM that are separated by two H lattice points, presented in Figure S3. The corresponding distance between the COM of the two PCBMs, presented in Figure 5 (d), is 0.92 nm. This specific arrangement for carbonyl oxygen atoms and COM of PCBMs is referred to as “Type A ordering”, presented in Figure 5 (e). It is also evident that the COM distances between PCBMs are relatively smaller for (110) perovskite surface compared to the (100) surface. As a result, a deposited film comprising solely “Type A ordering” is expected to be relatively denser on the (110) surface, which can lead to potentially efficient charge transport through the ETL. The peak positions at 0.8 nm in Figures 5 (a) and (c) indicate distances between two carbonyl oxygen atoms corresponding to “Type B ordering” for (110) and (100) perovskite surfaces, respectively. The distance 0.8 nm corresponds to two carbonyl oxygen atoms that are aligned diagonally on the (110) surface, while for (100) surface the distance indicates two neighboring PCBMs along Y axis, presented in Figures S2 and S3, respectively. The distances between COM of PCBMs for (110) surface for corresponding “Type B ordering” is 0.96 nm, while it is at 1.03 nm for (100) surface, as shown in Figures 5 (b) and


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(d), respectively. Following similar discussion as for “Type A ordering”, the COM distances for “Type B ordering” are relatively smaller for (110) surface, which signifies a more densely packed film of PCBMs on top of (110) perovskite surface compared to (100) perovskite surface. The peak positions at 0.59 nm and 0.4 nm in Figure 5 (a) correspond to distances between two neighboring carbonyl atoms, which are attached with Pb atom of (110) perovskite surface. Presence of two peaks (C and C1) within very short distances is likely due to the attachment of carbonyl oxygen on the periphery of the relatively large Pb atoms, presented in Figure S2. The corresponding COMs of PCBMs are at 1.05 nm, presented in Figure 5(d). This specific orientation of PCBMs refers to “Type C ordering”. On the other hand, for (100) surface, the corresponding distances between two carbonyl oxygen atoms and COM of PCBMs are 0.5 nm and 1.14 nm respectively, presented in Figure 5 (c) and Figure 5 (d). As a result, it is clear that for “Type C ordering”, PCBM film on top of the (110) surface will be more densely packed compared to that on (100) surface. By analyzing distinct types of ordering of the deposited PCBMs on different perovskite surfaces, we conclude that in general PCBMs on top of (110) surface form more densely packed layers compared to that on (100) surface. Moreover, among all the configurations, the COMs of PCBMs are the closest to each other for “Type A ordering”. Therefore, we speculate that “Type A ordering” of PCBMs on (110) perovskite surface might lead to more efficient electron transport compared to that on (100) perovskite surface. A more definitive conclusion is contingent on theoretical calculations of charge transport and corresponding energy barriers, which is beyond the scope of the present work. 4. CONCLUSION In conclusion, results from our molecular simulations suggest that the ester moiety of PCBM faces towards the (110) and (100) planes of perovskite surfaces during solution-processed 17 ACS Paragon Plus Environment


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deposition, while the fullerene moiety faces away from the surfaces. In the case of (110) surface, the strongest association occurs between the carbonyl oxygen atom of PCBM and the Pb atom of perovskite, while no significant coordination occurs between the phenyl moiety and the surface. On the other hand, for the (100) surface, the phenyl moiety has weak associations with the perovskite surface in addition to the dominant associations between the carbonyl oxygen atom of PCBM and the H atoms of the surface. The calculated self-diffusion coefficients of the carbonyl oxygen atoms of deposited PCBMs indicate a more stable anchoring on the (110) surface compared to that on the (100) surface. However, a two-pronged anchoring occurs in the latter case with associations of surface atoms with both carbonyl oxygen and phenolic group. As a result, we hypothesize that the mechanism of electron transfer for these two perovskite surfaces are somewhat different. Further ab initio calculations are necessary to compare the effectiveness of electron transfer from the two surfaces. While the ester moiety of PCBM actively takes part in electron transfer for the (110) surface, both ester and phenyl moiety participate in electron transfer on the (100) surface. By analyzing the in-plane ordering of PCBMs on perovskite surfaces, we conclude that PCBMs on top of (110) surface form a more densely packed monolayer compared to that on (100) surface with favorable associations of fullerene moieties that might lead to more efficient transport of electrons through the ETL deposited on (110) surface compared to that in the vicinity of (100) surface of perovskite. Supporting information Composition of the simulated systems, partial charges on the atoms of solvated PCBM based on DFT calculations, estimated ∆G value for the deposition of PCBM and atomistic configuration of the (110) and (100) perovskite surfaces with anchored carbonyl oxygen of PCBM.


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