This is the accepted version of the article: Urzúa-Leiva R., Narymany Shandy A., Xie H., Lira-Cantú M., Cárdenas-Jirón G.. Effects of the methylammonium ion substitution by 5-ammoniumvaleric acid in lead trihalide perovskite solar cells: a combined experimental and theoretical investigation. New Journal of Chemistry, (2020). 44. : 14642 - . 10.1039/d0nj02748k. Available at: https://dx.doi.org/10.1039/d0nj02748k Please do not adjust margins ARTICLE Effects of the methylammonium ion substitutions by 5- ammoniumvaleric acid in lead trihalide perovskite solar cell: A Received 00th January 20xx, Accepted 00th January 20xx combined experimental and theoretical investigation DOI: 10.1039/x0xx00000x Rodrigo Urzúa-Leiva*a, Amir Narymany Shandyb, Haibing Xieb, Mónica Lira-Cantú*b, Gloria Cárdenas-Jirónc In the last decade, lead triiodide perovskite (APbI3) (A: organic cation) solar cells (PSC) have been broadly studied due to its promising features related to the low cost, easy manufacturing process, and stability. Strategies to improve device stability include the application of technics such as compositional engineering of the cation of these halide perovskites, but it is still a complex task to find the right balance between stability and power conversion efficiency of materials and complete devices. In this work, we performed a combined study of five samples of the [5-AVA(1-x)MAx]PbI3 (5-AVA: ammonium valeric acid and MA: methylammonium) with x=1.0, 0.75, 0.5, 0.25 and 0.0, using X-Ray diffraction (XRD) and UV-VIS spectroscopy measurements in combination with periodic density functional theory (DFT) based calculations. Our samples showed an optical bandgap of 1.58 eV and the coexistence of the two phases as observed by XRD analyses. Theoretical results of the bandgaps for the no mixed phases (x=1.0 and x=0.0) show good agreement with the experiment, obtaining bandgap values overestimated by 0.18 eV and 0.33 eV, respectively. A direct relation between the amount of 5-AVA ions in the samples and the stability of the phases was theoretically found, proved through the increment observed in the bandgap and the cohesive energy. We proposed a compositional strategy to the perovskites [5-AVA(1-x)MAx]PbI3 with x values at most of 0.5, based on the small blue-shift and the low absorbance reduction of the spectrum curve, added to the small phase stabilization found. linking additives5 or compositional engineering.6, 7 The most Introduction typical and studied PSC is methylammonium lead trihalide, MAPbX3 (MA=methylammonium and X=Cl–, Br–, I–) with In the last decade, scientific research that concerns with green excellent optoelectronic properties associated to large light power generation of electricity has experienced a growing absorption coefficients, optimal band-gaps, and large carrier demand for new materials and technologies to deal with global diffusion lengths.8-10 Despite the growing interest, the warming and become a real alternative to fossil fuels. In this development of PSCs has not been free of major issues such as context, the electricity produced by photovoltaic solar cells is poor material stability under operational conditions 11-15 and an outstanding source of energy due to its abundance and toxicity due to the use of lead as a metallic center, the later eternal nature. The last biggest scientific breakthroughs in this has limited the deployment and commercialization of PSCs as a area befall the year 2009, with the invention of the perovskite future PV technological solution. 16 Different strategies have solar cells (PSCs),1 going on a few years from 3.8% to 25.2% been proposed to circumvent these problems, for example in a power conversion efficiency.2-4 Others important benefits of recent publication17, several potential substituents for the the PSCs come from the low cost compared with conventional replacement of lead such as Sn,18 Ge,19 and Sb,20 among solar cells, associated with inexpensive materials, easy others, has been reviewed, reaching efficiencies of 8.4%, 3.2%, manufactured process and high stability reached using cross- and 3.8%, respectively. On the other hand, the stability problems can be associated with intrinsic factors as the a. Institutode Ciencias Químicas Aplicadas, Facultad de Ingeniería, Universidad crystalline structure and chemical stability, as also as extrinsic Autónoma de Chile, Av. Pedro de Valdivia 425, 7500912, Providencia, Santiago, factors as moisture, UV radiation, and thermal stress. 12, 13, 21-23 Chile. b. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC, and the The correct combination of these two key aspects is necessary Barcelona Institute of Science and Technology (BIST), Bellaterra E-8193, Spain. to reach new PSCs aligned with the spirit of green power c. Laboratory of Theoretical Chemistry, Faculty of Chemistry and Biology, University generation. Moreover, in line with chemical stability, potential of Santiago de Chile (USACH), 9170022, Santiago, Chile. *Author to whom the correspondence should be addressed: substituents of the organic part have also been addressed. The rodrigo.urzua@uautonoma.cl, monica.lira@icn2.cat replacement of the cationic MA by different atoms or Electronic Supplementary Information (ESI) available: [details of any supplementary information available should be included here]. See molecules has been intensely studied with favourable DOI: 10.1039/x0xx00000x improvement in device stability, for example, formamidinium Please do not adjust margins Please do not adjust margins ARTICLE Journal Name (FA), Cesium (Cs) and 5-ammonium valeric acid (5-AVA) have Theoretical details been analysed.24, 25 Han et al.,26 made a significant At low temperature, the crystallographic phase of perovskite contribution to the state of the art of PSCs by proposing a MAPbI3 has orthorhombic symmetry, with the MA ion ordered hole-conductor-free perovskite based on a mixed of MA and 5- in the unit cell as shown in Fig. 1. The well-defined position of AVA iodide with lead(II) iodide. The results showed that the MA ions in the crystallographic unit cell is useful to make the crystalline structure is less pore defect, improved the TiO 2 substitutions of these ions by 5-AVA ions and keep invariant scaffold contact, resulting in a longer exciton lifetime with a the dipole moment of the unit cell. We use the crystalline higher quantum yield efficiency and high stability in air structure reported by Baikie et. al. 32 as the starting point, ambient conditions compared to MAPbI3. Later, Nazeeruddin where we apply a systematic substitution of MA ion et al.,27 achieved a one-year stable perovskite solar cell using coordinates by 5-AVA ion, using the same orientation of the interface engineering precisely using the combination of MA native zwitterion. Following the experiment samples, a total of and 5-AVA, confirming the appropriated use of 5-AVA has a five different phases of [5-AVA(1-x)MAx]PbI3 was theoretically substituent.28 In the later work, the beneficial effect of modelled, with x taking values of 1.0, 0.75, 0.5, 0.25, and 0.0. applying two mesoporous oxide layers 28, 29 in combination with We perform a constrained geometry optimization on these the use of 5-AVA dopants and the elimination of a hole structures keeping all unit cell angles fix to conserve the transport layer, was suggested as the reasons behind the symmetry. All geometry optimization calculations were based remarkable device stability. Relatively few computational on DFT,33 where the generalized gradient approximation of investigations of mix MA/5-AVA lead trihalide have been Perdew-Burke-Ernzerhof (PBE)34 was used to represent the performed30, 31 and to the best of our knowledge, limited exchange and correlation energy of the electrons using the connection with experimental results have been shown. Quantum-Espresso code35. Semi-empirical van der Waals In this work, we present an experimental and theoretical corrections were considered by the use of Grimme’s D3 combined study of the global and molecular effects on a correction.36 Moreover, the plane wave (PW) technique along systematic increase of 5-AVA concentration in the preparation with PAW37 pseudopotential was employed, using an energy of perovskite [5-AVA(1-x)MAx]PbI3 crystals. Moreover, from the cutoff of 400 Ry with a uniform Monkhorst-Pack38 scheme of theoretical point of view, we analyse the molecular and optical 7-5-7 k-points grid to sampling the entire Brillouin zone. The implications of the substitution of MA by 5-AVA ions using the convergence tolerance for the total energy and Hellmann– framework of density functional theory (DFT) and the plane Feynman force during the structural relaxation was set to 10 −5 wave methods. eV and 0.01 eV/Å, respectively. To an easy identification of the calculation scheme, we denote this strategy of calculation as DFT-PW/PBE-D3. Experiments and calculation methods On the other hand, accurate energy, band-structure, and DOS Experimental details (density of states) were determined through a single point The [5-AVA(1-x)MAx]PbI3 samples of five phases from x=0 to 1, calculation in the previously optimized geometry using the with intermediate values of 0.25, 0.50 and 0.75, were ADF-BAND program.39, 40 We study the scalar relativistic effects synthesized and analysed by XRD to study the crystalline through the inclusion of ZORA formalism in an all-electron (AE) quality and composition of the materials. Moreover, a calculation of the already mentioned properties using also the bandgap determination via UV-VIS measurement in the five functional PBE-D3 with a triple-ζ basis set. We denote this phases was performed. For the preparation of the [5-AVA(1- strategy of calculation as DFT-AE/PBE-D3. x)MAx]PbI3 samples, PbI 2, MAI and 5-AVA were dissolved in a 1:4 mixture of dimethyl sulfoxide (DMSO) and dimethylformamide (DMF), with the respective variation of the molar ratio between 5-AVA and MAI. The Glass/FTO substrates were cleaned with Hellmanex/distilled water/acetone/ethanol in sequence using an ultrasonic bath. Just before the material deposition via Spin-Coating in the Glovebox, the samples were plasma-etched to increase the wettability of the sample surface. After the dynamic spin coating, the samples were heated for 20 minutes at 100 °C and taken out of the glovebox to perform measurements. The UV-VIS spectra were measured in a Cary 4000 UV-VIS Spectrometer with a wavelength spectrum from 200 to 800 nm. To minimize systematical errors, a Glass/FTO reference was measured and its baseline Figure 1. Schematic representation of the crystalline structure of the orthorhombic phase of MAPbI3 . A well-resolved position and orientation of MA was subtracted from the data of the samples. ions are appreciable at this symmetry. The XRD-analysis was performed with a 2-Theta range from 5 to 60 degrees including a glass/FTO substrate as reference. 2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE RESULTS AND DISCUSSION the UV-VIS spectra in Fig. 4, and starting from the MAPbI3 reference absorption curve, we observe a consistent transition Structural and UV-VIS characterization of the absorption peaks towards the optical bandgap of the 5- The XRD analysis of the samples shows a good agreement with AVAPbI3 with an energy gap of 2.33 eV. The optical gap of the the already published XRD-properties of the perovskite,41 as samples shows in Table 1, was estimated by the extrapolation shown in Fig. 2. All peaks can be assigned either to the of the linear region at the beginning of each absorption peak substrate (2=26.4º), an excess of PbI2 (2=12.6º), or the to the x-axis intercept, as indicated by the grey dashed lines in phase MAPbI3 (2= 14.8º, 20.1º and 24.5º).42 The presence of Fig. 4. On the other hand, Table 1 also shows the values of the PbI2 is known to be beneficial for PSCs. Its passivation effect principal absorptions bands obtained from the absorption leads to the reduction of halide defect concentration (halide curves derivatives (Fig. 1 Supporting Information). Two vacancies), resulting in longer carrier lifetime. 43 However, it characteristic bands in the visible region of the spectra are can also result in inhibited charge transport and an increase in appreciable in all samples containing a fraction of the MA the degradation of the halide perovskite layer (due to the cation, one at low energy and a second one at higher energy. photodecomposition of PbI2). To overcome this issue, the The two bands have energies of 1.6 eV and 2.5 eV, incorporation of organic additives or ligands, such as AVAi, respectively. The remaining sample, which contains only 5-AVA helps to regulate the homogeneous distribution of PbI 2 in the cation, confirms the absence of the first characteristic halide perovskite thin film and to improve thin film absorption band, suggesting that it is originated due to the properties.44, 45 Thus, there is an optimal amount of AVAi effect of the MA ion on the cavity. Using theoretical concentration incorporated within the halide perovskite. As calculations we analysed in more detail the effect of the MA seen in Fig. 3, the optimal concentration of AVAi in the and 5-AVA ions in the bands of the Fermi level frontier. samples is at ~x=0.25 (for x in [5-AVA(1-x)MAx]PbI3), above this Table 1. Optical band-gap and principal absorption peak of the different phases of the value, the excess of PbI2 is clearly observed by the increase of [5-AVA(1-x)MAx]PbI3 obtained from the UV-Vis absorption spectra and corresponding the PbI2 peak at 12.6º.42 This MAPbI3-XRD pattern is then derivatives, respectively. compared with the other [5-AVA(1-x)MAx]PbI3 samples, as can be seen in Fig. 3. The very significant peaks for the 5-AVA [AVA(1-x)MAx]PbI3 Optical band-gap (eV) Absorption peak (eV) containing samples at 5.8°, 7.8°, 9.4°, attributed to x=1 1.58 1.63 crystallographic planes of the formation of a 2D perovskite, are x=0.75 1.59, 2.14 1.65, 2.47 in good agreement with previously reported data,26, 27 and can x=0.50 1.60, 2.25 1.66, 2.47 be assigned to 5-AVAPbI3.46 It has previously suggested that x=0.25 1.59, 2.30 1.65, 2.46 the 5-AVAi, MAI and PbI2 can form 2D Ruddlesden−Popper x=0 2.33 2.45 (RP) phases of AVA2(CH3NH3)n−1PbnI3n+1 perovskite structure.30 However, the concentration ratios used of each reactant are slightly different than the ones used in this work. Finally, we observe that the XRD pattern of the [5-AVA(1-x)MAx]PbI3 (x = 0.25, 0.50, 0.75) show two sets of peaks, which can be assigned to either MAPbI3 or 5-AVAPbI3. This indicates the coexistence of these two phases in the samples and is in good accordance with the results of UV-VIS analysis. Figure 2. Comparison of the experimental XRD data with the published data of Yamada, Y et. al.41 (CSID data) for MAPbI3. All peaks can be assigned either to the perovskite, the substrate, or the PbI2. Figure 3. XRD analysis of the five [5-AVA(1-x)MAx]PbI3 samples depending of the 5- The UV-Vis absorption spectra, Fig. 4, show that MAPbI3 AVAi content. The coexistence of the two phases, MAPbI3 and 5-AVAPbI3, are verified by the observable phase transition between the two configurations. achieved an optical bandgap of 1.58 eV, which agrees with others published works reporting bandgaps of 1.6 eV,47-50 making the reference samples of this series reliable. Analysing This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 3 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name Figure 4. Absorption spectra of the different phases of the [5-AVA(1-x)MAx]PbI3. Two optical transitions corresponding to bandgap energies of 1.58 eV and 2.33 eV for the MAPbI3 and 5-AVAPbI3 respectively, can be observed. Theoretical results Based on the optimized geometry of atomic coordinates and lattice parameters, and maintaining the lattice orthogonally fixed as discussed above, we found an excellent performance of the DFT-PW/PBE-D3 calculation scheme for reproducing the published crystallographic data. The experimental lattice parameters (a=8.836 Å, b=12.58 Å and c=8.555 ) used to Figure 5. The behaviour of theoretically predicted lattice parameter a (a) and compare our theoretical results in Fig. 5(a) was obtained from bandgap (b) in the different phases of [5-AVA(1-x)MAx]PbI3 studied compared with the ref.32 and ref.51 in (a), and with our experimental values of MAPbI3 phase in the ref.32, determinates by single crystal X-ray diffraction at (b). 100 K and structure solution using the Superflip algorithm. An additional lattice parameter from the ref.51 was included in Fig. The systematic substitution of MA by 5-AVA ions in a single 5(a) as other sample to compare our results. The DFT-PW/PBE- unit cell of the orthorhombic phase of MAPbI 3 shows a clear D3 scheme of calculation only overestimates a maximum of tendency over the size of lattice parameter a and the bandgap 1.4 % of the lattice vector a in the MAPbI3 phase. For the of the single crystal cell, finding both a direct relation with the bandgap, we obtained a value of 1.7 eV, in agreement with increment of 5-AVA ions in the cell, as shown in Fig. 5. As reported values,52, 53 showing not-dependency on the DFT- expected, a large effect in the volume of the cell is PW/PBE-D3 or DFT-AE/PBE-D3 scheme of calculation. In other appreciable, which is coherent with the increase of ionic radii words, the scalar relativistic effect considered at the DFT- values from 2.17 Å to 5.44 Å for MA and 5-AVA, respectively, AE/PBE-D3 scheme is negligible over this parameter. On the calculated according to equations of Cheetham et. al. 55 The other hand, the obtained bandgap value, using the empirical increase of the ionic radii is two times larger when MA is dispersion correction D3, is 0.1 eV which is smaller than its replaced by 5-AVA. As a results of the accommodation of this counterpart (before correction), and although minimal, the large new organic ion, the calculated bond distances of Pb-I in volume of the unit cell is observed to be reduced. This result is the quasi-octahedral PbI6 is increased from 3.2 Å in the pure in agreement with other published works,52, 54 and indicates phase MAPbI3 to more than 4.0 Å in the pure phase AVAPbI 3. that for the appropriate treatment of the ionic interaction in This structural change has a direct relation with the large this type of crystals, it is necessary to include some correction effect measured in the theoretical bandgap from the minimal to the dispersion interactions. substitution of MA by 5-AVA. From an energetic point of view, the calculated bandgaps show in Fig. 5(b) of the pure phases, MAPbI3 (1.76 eV) and 5-AVAPbI3 (2.63 eV), are in good agreement with our experimental measures of the principal absorptions bands show in Table 1. However, the bandgaps calculated for the mixed phases (x=0.75, 0.5, and 0.25) have a very poor agreement with the measured experiment values. We can attribute this discrepancy to that the theoretical perovskite model used is based on the pure and infinitely periodic 3D orthorhombic structure of MAPbI3, whereby construction the substitution of MA ions by 5-AVA is homogeneously replicated through the crystal. Large theoretical bandgap values are a result of the strong distortion of the octahedral PbI6 structure due to the incorporation of AVA ions in the cavity of the MA ion. In contrast, as already explained, the samples analysed experimentally can present 4 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE subdomains corresponding to pure 3D and 2D perovskite (see Fig. 7 of the schematic model),46 each with characteristic optical transitions observable in the spectrum, as shown in Fig. 4. For example, with a 1:4 ration for 5-AVA:MA ions, we can suppose a full substitution of MA ion only in the surfaces unit cell or close to them, and not substitution in the bulk of the crystal (Fig. 7b). Our experiment reflects well this phenomenon, as previously discussed, showing the two characteristic absorption bands in the mixed samples. Nevertheless, the theoretical bandgaps show the mixed samples transition to the full substituted 5-AVA unit cell, with a systematic increment of the bandgap value 1.74 eV <2.11 eV <2.18 eV <2.48 eV <2.51 eV in the same order that the substitution index increment of 5-AVA in the [5-AVA(1- x)MAx]PbI3 samples. We attribute the increase of the bandgaps to a stabilization of the frontier conduction bands (valence band and conduction band) associated mainly to the formation Figure 7. (a) Schematic representation of a Carbon-based Perovskite solar cell of unoccupied orbitals from the 5-AVA ion closed to the Fermi where the perovskite is introduced by infiltration. (b) Schematic representation of the AVAi molecule an its interaction with the MA halide perovskite. level, as shown in Fig. 7c. Another important energetic aspect associated with the stability of the cell is the value of the From an electronic structure point of view, the DOS and pDOS cohesive energy. The calculated cohesive energy of the five of MAPbI3 in the vicinity of Fermi level, shows a typical phases was performed following the procedure developed by distribution also observed in other published works.56-58 The Yong-Hyon et al.54 Fig. 6 shows that the cohesive energy is in valence bands maximum (VBM) is mainly on the iodide atoms line with the values reported for MAPbI3, and also agree with and the conduction bands minimum (CBM) belong to lead the experimental results on the gain in the stability of atoms, as shown in Fig. 8a. Also, the orbital projections of perovskite crystal by partial substitution of MA ions by 5-AVA these bands respond to typical p-character in both iodide and ions. In contrast to what we might think about the adverse lead atoms of MAPbI3 crystal (see Fig. 8b). On the other hand, effect on stability due to the strong structural distortion in this phase of perovskite, the MA bands are negligible in the caused by the ionic radius of 5-AVA, the stability of the unit frontier of the Fermi level. Thus, once the systematic cell is favoured, being even 1.8 eV higher in the phase 5- substitution of MA by 5-AVA takes place, a rearrangement of AVAPbI3 in comparison with the one of MAPbI3. This result is the frontier bands in all cases is observed (Fig. 2 Supporting also related to the increase of the bandgaps values, as Information), being mostly appreciable in the CB edge. In the previously discussed. case when MA is completely substituted, the CB edge mainly localized over Pb atoms in the MAPbI 3 phase, changes to localization on the 5-AVA ion with mostly p-character bands, in 5-AVAPbI3 phase (see Figs. 8c and 8d). In contrast, the VB edge is almost unaffected by the substitution, with a minimal occurrence of 5-AVA states closed to the frontier of the Fermi level. The presence of metallic Pb in halide perovskites, indicates that Pb is unsaturated and thus, iodine deficiencies may also be present in the perovskite lattice of the reference sample.59 This implies that the application of additives, such as AVAI, can effectively suppress the formation of metallic Pb via either direct electron donation to unsaturated Pb or immobilization of iodine as already reported.44, 45 Additionally, Figure 6. Calculated cohesive energy for the different phases of [5-AVA(1- our theoretical results show an increment of the PbI distances x)MAx]PbI3 compared with the work of ref [51]. with the inclusion of 5-AVA ions in the unit cell, resulting in a most favourable interaction of 5-AVA ions with the unsatured Pb atoms, appreciable through the appearance of 5-AVA states in the CBM, as shown in Fig. 8(c). A qualitative description of these bands in the frontier region is shown in Fig. 3 of Supporting Information. This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 5 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name 10 10 (a) Total (c) Total 8 8 MA AVA DOS (arb.) DOS (arb.) 6 Pb 6 Pb I I 4 4 2 2 0 0 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 2 Energy (eV) Energy (eV) 10 10 (b) Pb-s (d) Pb-s 8 8 Pb-p Pb-p DOS (arb.) DOS (arb.) 6 I-s 6 I-s I-p I-p 4 4 2 2 0 0 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 2 Energy (eV) Energy (eV) Figure 8. DOS and pDOS calculated at DFT-AE/PBE-D3 level of theory for the phases MAPbI3 (a) and (b), and 5-AVAPbI3 (c) and (d). For a better appreciation, pDOS is separated by atoms (Pb,I) and orbital (s,p). The optical properties, in particular, the imaginary part of the dielectric constant (ɛ2) were determined with SIESTA program60 through a single point calculation of the converged geometry of five phases [5-AVA(1-x)MAx]PbI3. The real part of the dielectric constant (ɛ1) was extracted from ɛ2 using the Kramers-Kronig method.61 Finally, the frequency-dependent absorption coefficient (α) is given by: 𝜖1 (𝜔) + √𝜖1 (𝜔)2 + 𝜖2 (𝜔)2 𝛼(𝜔) = 𝜔√ 2 With this equation, we compared the experimental UV-Vis absorptions curves with the simulated curves of alpha obtained from calculated theoretical models of the five samples of perovskite studied in this work. Figure 9. Simulated curves of the absorption coefficient calculated for the five phases of [5-AVA(1-x)MAx]PbI3 (short dashed lines) compared with our UV-Vis The results of the simulated curves obtained from the spectrum of MAPbI3 (black line). dielectric function, showed a direct relation of the blue-shift of the absorption coefficient with the systematic increment of 5- AVA ions in the unit cell model (see Fig. 9). However, the phases with x=0.25 and x=0.5 show a very small shift (<0.2 eV) Conclusions respect to the reference curve of MAPbI3. The calculated In summary, we generate a series of five [5-AVA(1-x)MAx]PbI3 curves show less blue-shift that other modified perovskites samples with a well-established procedure which resulted in a used to improve stability, like for example, the substitution of reliable sample to perform measures of XRD and UV-Vis iodine by chloride or iodine by bromide. 23 This result indicates absorptions. The XRD results show the coexistence of the that the substitution of MA by 5-AVA in low quantities can MAPbI3 and 5-AVAPbI3 phases and a well-defined transition maintain the optical properties similar to the original MAPbI 3 between the samples. The same behaviour is obtained from perovskites, improving the global stability of the crystal, as was the absorption spectra, resulting in promising optical previously shown. bandgaps of 1.58 eV for MAPbI3 and 2.33 eV for 5-AVAPbI3. Using theoretical calculations, we found reliable agreement between the experimentally measured bandgaps and the calculated values, for the pure phases. By contrast, poor agreement for the transition samples was found. On the other hand, a direct relationship between the cell stability (through the growth of cohesive energy) and the 5-AVA rate of substitution was found, also tightly related to the systematic increment of the theoretical bandgaps. The DOS and pDOS of the samples showed that apparently, the presence of atomic orbitals of 5-AVA in the CB zone closed to the Fermi level provokes a larger bandgap, which could be attributed to a less 6 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE reactivity of the perovskite with respect to the other Moser, M. Grätzel and N.-G. Park, Journal, 2012, 2, 583- derivatives62-64. Finally, this work shows that the moderated 587. substitution of MA ion by 5-AVA ions in perovskite lead-based 11. M. V. Khenkin, E. A. Katz, A. Abate, G. Bardizza, J. J. Berry, solar cells allows modulating several key aspects of the cell C. Brabec, F. Brunetti, V. Bulović, Q. Burlingame, A. Di Carlo, R. Cheacharoen, Y.-B. Cheng, A. Colsmann, S. Cros, with the purpose to drive eventually the design of new K. Domanski, M. Dusza, C. J. Fell, S. R. Forrest, Y. Galagan, materials. D. Di Girolamo, M. Grätzel, A. Hagfeldt, E. von Hauff, H. Hoppe, J. Kettle, H. Köbler, M. S. Leite, S. Liu, Y.-L. Loo, J. M. Luther, C.-Q. Ma, M. Madsen, M. Manceau, M. Conflicts of interest Matheron, M. McGehee, R. Meitzner, M. K. Nazeeruddin, There are no conflicts to declare. A. F. Nogueira, Ç. Odabaşı, A. Osherov, N.-G. Park, M. O. Reese, F. De Rossi, M. Saliba, U. S. Schubert, H. J. Snaith, S. D. Stranks, W. Tress, P. A. Troshin, V. Turkovic, S. Acknowledgements Veenstra, I. Visoly-Fisher, A. Walsh, T. Watson, H. Xie, R. Yıldırım, S. M. Zakeeruddin, K. Zhu and M. Lira-Cantu, We are thankful for the financial support from USACH under Nature Energy, 2020, 5, 35-49. the Project POSTDOC_DICYT, Código 021941CJ_POSTDOC 12. A. Pérez-Tomás, A. Mingorance, D. Tanenbaum and M. (R.U.-L., G.C.-J.) Powered@NLHPC: This research was partially Lira-Cantú, in The Future of Semiconductor Oxides in Next- supported by the supercomputing infrastructure of the NLHPC Generation Solar Cells, ed. M. Lira-Cantu, Elsevier, 2018, (ECM-02) of the Universidad de Chile. M.L.C. and H.X. DOI: https://doi.org/10.1016/B978-0-12-811165-9.00008- acknowledge the support from Spanish MINECO for the grants 9, pp. 267-356. ENE2016-79282-C5-2-R and PID2019-104272RB-C54 the 13. Y. Reyna, A. Pérez-Tomás, A. Mingorance and M. Lira- Cantú, in Molecular Devices for Solar Energy Conversion OrgEnergy Excellence Network CTQ2016-81911- REDT, the and Storage, eds. H. Tian, G. Boschloo and A. Hagfeldt, Agència de Gestiód'Ajuts Universitaris i de Recerca (AGAUR) Springer Singapore, Singapore, 2018, DOI: 10.1007/978- for the support to the consolidated Catalonia research group 981-10-5924-7_13, pp. 477-531. 2017 SGR 329 and the Xarxa de Referència en Materials 14. Y. Reyna, M. Salado, S. Kazim, A. Pérez-Tomas, S. Ahmad Avançats per a l'Energia (Xarmae). ICN2 is supported by the and M. Lira-Cantu, Nano Energy, 2016, 30, 570-579. Severo Ochoa program from Spanish MINECO (Grant No. SEV- 15. T. A. Berhe, W.-N. Su, C.-H. Chen, C.-J. Pan, J.-H. Cheng, 2017-0706) and is funded by the CERCA Programme / H.-M. Chen, M.-C. Tsai, L.-Y. Chen, A. A. Dubale and B.-J. Generalitat de Catalunya. Hwang, Energy Environ. Sci., 2016, 9, 323-356. 16. N. K. Noel, S. D. Stranks, A. Abate, C. Wehrenfennig, S. Guarnera, A.-A. Haghighirad, A. Sadhanala, G. E. Eperon, Notes and references S. K. Pathak, M. B. Johnston, A. Petrozza, L. M. Herz and H. J. Snaith, Energy Environ. Sci., 2014, 7, 3061-3068. 1. A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, J. Am. 17. R. Kour, S. Arya, S. Verma, J. Gupta, P. Bandhoria, V. Formatted: Font: (Default) Calibri, 12 pt, Do not check Chem. Soc., 2009, 131, 6050-6051. Bharti, R. Datt and V. Gupta, Global Challenges, 2019, 3, spelling or grammar, Character scale: 100% 2. E. H. Jung, N. J. Jeon, E. Y. Park, C. S. Moon, T. J. Shin, T.-Y. 1900050. Yang, J. H. Noh and J. Seo, Nature, 2019, 567, 511-515. 18. D. B. Mitzi, C. A. Feild, Z. Schlesinger and R. B. Laibowitz, 3. M. A. 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