Efficiency and Stability Enhancement in Perovskite Solar Cells by Inserting Lithium‐Neutralized Graphene Oxide as Electron Transporting Layer

Abstract

wileyonlinelibrary.comthe theoretical values, [ 9 ] further work is needed to increase the fi ll factor (FF) that today remains the bottleneck for the PCE enhancement. In this context, the optimization of interfaces between absorber, carrier transport layers, and electrode contact layers is crucial for an effi cient carrier transport. Thus, to improve the PCE of the PSCs, three main aspects need to be taken into account: the band alignment, the interface structure, and its passivation. [ 9 ] Furthermore, it must be taken into account that the injection times of electrons and holes in PSCs have been measured to be 0.4 and 0.6 ns, respectively, which are still orders of magnitude longer than the hot carrier cooling (or thermalization) time (≈0.4 ps). [ 10 ] Thus, a large amount of the converted photon energy is wasted in the thermalization process and in the carrier trapping. In this context, several materials have been proposed to facilitate electron/ hole extractions, including fullerene, [ 11 ] graphene, [ 12 ] or core/ shell metal nanoparticles. [ 13 ] Although graphene-based materials have been demonstrated to improve the performance and stability of organic and hybrid photovoltaic devices as recently reviewed by Singh and Nalwa, [ 14,15 ] a direct evidence is yet to be obtained regarding their role as a fast electron injector rather than just an electron trapping center. [ 16 ] In this work, to improve the electron extraction from the perovskite absorber into the mesoporous TiO 2 , an additional lithium-neutralized graphene oxide (GO-Li) layer as electron transporting Layer (ETL) is used. GO-Li has been already used as ETL in organic photovoltaic devices by Kakavelakis et al. [ 17 ] The authors demonstrated that the replacement of H atoms in the carboxyl groups of GO by Li atoms can effectively reduce the working function (WF) of GO from 4.9 to 4.3 ± 0.1 eV. Due to low electronegativity and low WF, Li atoms lose their valence electrons to the GO plane, and the resulting positive Li + induces dipoles. This transfer of charge from the metal to the GO leads to a shift in the Fermi level toward the vacuum and a consequent decrease in WF. [ 18 ] Since the WF of GO-Li displays a good match with the Lowest Unoccupied Molecular Orbital (LUMO) level of mesoporous TiO 2 , in this work a new effi cient perovskite solar cell structure is proposed which includes the GO-Li as an interlayer between the TiO 2 and the perovskite harvester. The resulting PSCs exhibit enhanced J SC and FF and reduced Effi ciency and Stability Enhancement in Perovskite Solar Cells by Inserting Lithium-Neutralized Graphene Oxide as Electron Transporting LayerAntonio Agresti , Sara Pescetelli , Lucio Cinà , Dimitrios Konios , George Kakavelakis , Emmanuel Kymakis , and

Carrier Interfacial Engineering by Bismuth Modification for Efficient and Thermoresistant Perovskite Solar Cells

“…The equivalent circuit used to fit the data is shown in the inset of Figure 2c. [43] Compared with the control perovskite film, 1 and 3 nm blue shifts are observed for MB 1.5 and MB 2.0 films, respectively. [39,40] From the fitting results in Figure S16 and Table S3 (Supporting Information), similar R s values of 10.1 and 10.2 Ω cm 2 are obtained due to the identical FTO and gold conductive electrode in two devices.…”

p‐Type CuI Islands on TiO2 Electron Transport Layer for a Highly Efficient Planar‐Perovskite Solar Cell with Negligible Hysteresis

“…Previously, Kamat and co-workers and Deng and and co-workers independently employed a CuI layer as a p-type hole conductor instead of the organic hole conductor (spiro-OMeTAD) or PEDOT:PSS in an n-i-p-type meso-PSC [24] or a p-i-n-type planar-PSC, [25] respectively. [2] It is noticed that Carlo and coworkers reported how PbI 2 at the interface between TiO 2 ETL and perovskites prevents the back-recombination, [27] and Qiao and co-workers reported how Li cation incorporated to neutralized graphene oxide between TiO 2 ETL and perovskites ETL improves electron extraction ability. [2] It is noticed that Carlo and coworkers reported how PbI 2 at the interface between TiO 2 ETL and perovskites prevents the back-recombination, [27] and Qiao and co-workers reported how Li cation incorporated to neutralized graphene oxide between TiO 2 ETL and perovskites ETL improves electron extraction ability.…”

Beneficial Role of Reduced Graphene Oxide for Electron Extraction in Highly Efficient Perovskite Solar Cells

“…[14][15][16] However, all of the PCEs reported are limited to less than 14 % and the perovskite was not formed as a perfect film, which casts the doubt on the real beneficial role of rGO on high-efficiency PSCs. In contrast to many applications of carbon-based materials that are usually introduced at the perovskite/TiO 2 or perovskite/HTM interfaces, or in substitution of the HTM itself, [17,18] here we propose a systematic study by exploring three different configurations as shown in Figure 1.We integrated the rGO: 1) in the 2,2',7,7'-tetrakis(N,N'-di-pmethoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) HTM, 2) in the matrix of the active perovskite layer, and 3) within the mesoporous TiO 2 (m-TiO 2 ) ETM. In this study, mesoscopic PSCs are composed of a fluorine doped tin oxide (FTO)-coated glass substrate, a compact TiO 2 layer followed by a m-TiO 2 layer, a mixed (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 (FA = formamidinium, MA = methylammonium) perovskite layer that infiltrates into the m-TiO 2 , a spiro-OMeTAD layer, and a Au counter electrode.…”

“…[14][15][16] However, all of the PCEs reported are limited to less than 14 % and the perovskite was not formed as a perfect film, which casts the doubt on the real beneficial role of rGO on high-efficiency PSCs. In contrast to many applications of carbon-based materials that are usually introduced at the perovskite/TiO 2 or perovskite/HTM interfaces, or in substitution of the HTM itself, [17,18] here we propose a systematic study by exploring three different configurations as shown in Figure 1.…”