Abstract
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.
Highlights
The goal of lowering solar electricity costs by improving the efficiency, reliability, and durability of emerging metal halide perovskite (MHP) solar cells (PSCs) is an intense area of research
Air, UV light, thermal stress, light soaking, and electric fields, among other agents, degrade the perovskite solar cells,[8,9] especially outdoors,[10] and prevent market requirements from bpereinsegnaccehoiefvmedo.isMtuHrePorralpigidhltyirervaodlivaetisonto.11P−b1I32 or PbOx in the Even in an inert atmosphere, the most representative perovskite absorber material, MAPbI3, appears to be thermally unstable as revealed by the observed transformation into PbI2.14 Stability is one of the main barriers preventing the widespread application of PSCs.[15,16]
Chen et al.[30] simultaneously incorporated N, S codoped G quantum dots (GQDs) in the electron transport layer (ETL)-perovskite interface and into the perovskite active layer of the PSC acting as a nucleating template, easing charge extraction and defect passivation, obtaining efficiency and stability improvements of the device
Summary
The goal of lowering solar electricity costs by improving the efficiency, reliability, and durability of emerging metal halide perovskite (MHP) solar cells (PSCs) is an intense area of research. Chen et al.[30] simultaneously incorporated N, S codoped GQDs in the ETL-perovskite interface and into the perovskite active layer of the PSC acting as a nucleating template, easing charge extraction and defect passivation, obtaining efficiency and stability improvements of the device. We have demonstrated a route for doping poly(3,4ethylenedioxythiophene)−poly(styrenesulfonate) (PEDOT:PSS) HTL with pristine G-nanoplatelets, obtaining significant improvement on conductivity without the loss of transmittance at concentrations well below percolation.[35] The integration of this G-doped HTL into inverted MAPbI3 solar cells resulted in more efficient devices due to an enhancement of charge extraction and a reduction of charge accumulation at the graphene−PEDOT:PSS interface as well as stability improvement under environmental conditions. This work demonstrates a simple route to obtain graphene/metal halide composites that can pave the way to the development of low-cost solar cells
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