Effect of Pristine Graphene on Methylammonium Lead Iodide Films and Implications on Solar Cell Performance

The relatively low stability of solar cells based on hybrid halide perovskites is the main issue to be solved for the implementation in real life of these extraordinary materials. Degradation is accelerated by temperature, moisture, oxygen, and light and mediated by halide easy hopping. The approach here is to incorporate pristine graphene, which is hydrophobic and impermeable to gases and likely limits ionic diffusion while maintaining adequate electronic conductivity. Low concentrations of few-layer graphene platelets (up to 24 × 10–3 wt %) were incorporated to MAPbI3 films for a detailed structural, optical, and transport study whose results are then used to fabricate solar cells with graphene-doped active layers. The lowest graphene content delays the degradation of films with time and light irradiation and leads to enhanced photovoltaic performance and stability of the solar cells, with relative improvement over devices without graphene of 15% in the power conversion efficiency, PCE. A higher graphene content further stabilizes the perovskite films but is detrimental for in-operation devices. A trade-off between the possible sealing effect of the perovskite grains by graphene, that limits ionic diffusion, and the reduction of the crystalline domain size that reduces electronic transport, and, especially, the detected increase of film porosity, that facilitates the access to atmospheric gases, is proposed to be at the origin of the observed trends. This work demonstrated how the synergy between these materials can help to develop cost-effective routes to overcome the stability barrier of metal halide perovskites, introducing active layer design strategies that allow commercialization to take off.We acknowledge financial support by the Spanish Ministry of Science and Innovation under Projects PID2020-115514RB-I00 (C.C.), MAT2015-65356-C3-2-R (A.A), and PID2019-107314RB-I00 (I.M-S). This work was partially supported by European Research Council (ERC) via Consolidator Grant (724424-No-LIMIT) (I.M-S), AYUDA PUENTE 2020 URJC (C.C.). Associated Lab LABCADIO belonging to Community of Madrid, CM, net laboratories ref 351 is also acknowledged (C.C.). T.S.R. acknowledges funding from CM and European Social Fund (ESF) under the Talento fellowship 2017-T2/IND-5586 and project F660 financed by CM and Rey Juan Carlos University under action 1, “Encouragement of Young Phd students investigation". C.R-O. acknowledges funding from the Spanish Ministry of Science and Innovation under a FPI predoctoral contract (PRE2019-088433)

Interface Engineering in Perovskite Solar Cells by Low Concentration of Phenylethyl Ammonium Iodide Solution in the Antisolvent Step

In spite of the outstanding properties of metal halide perovskites, its polycrystallinenature induces a wide range of structural defects that results in charge losses thataffect thefinal device performance and stability. Herein, a surface treatment is usedto passivate interfacial vacancies and improve moisture tolerance. A functionalorganic molecule, phenylethyl ammonium iodide (PEAI) salt, is dissolved with theantisolvent step. The additive used at low concentration does not induce formationof low-dimensional perovskites species. Instead, the organic halide species pas-sivate the surface of the perovskite and grain boundaries, which results in aneffective passivation. For sake of generality, this facile solution-processed synthesiswas studied for halide perovskite with different compositions, the standardperovskite MAPbI3, and double cation perovskites, MA0.9Cs0.1PbI3andMA0.5FA0.5PbI3, increasing the average photoconversion efficiency compared tothe reference cell by 18%, 32%, and 4% respectively, observed for regular, n-i-p,and inverted, p-i-n, solar cell configurations. This analysis highlights the generalityof this approach for halide perovskite materials in order to reduce nonradiativerecombination as observed by impedance spectroscopy