Sodium Diffuses from Glass Substrates through P1 Lines and Passivates Defects in Perovskite Solar Modules

Most thin-film photovoltaic modules are constructed on soda-lime glass(SLG)substrates containing alkali oxides,such as Na_(2)O.Na may diffuse from SLG into a module's active layers through P1 lines,an area between a module's constituent cells where the substrate-side charge transport layer(CTL)is in direct contact with SLG.Na diffusion from SLG is known to cause several important effects inⅡ-Ⅵand chalcogenide solar modules,but it has not been studied in perovskite solar modules(PSMs).In this work,we use complementary microscopy and spectroscopy techniques to show that Na diffusion occurs in the fabrication process of PSMs.Na diffuses vertically inside P1 lines and then laterally from P1 lines into the active area for up to 360 pm.We propose that this process is driven by the high temperatures the devices are exposed to during CTL and perovskite annealing.The diffused Na preferentially binds with Br,forming Br-poor,l-rich perovskite and a species rich in Na and Br(Na-Br)close to P1 lines.Na-Br passivates defect sites,reducing non-radiative recombination in the perovskite and boosting its luminescence by up to 5×.Na-Br is observed to be stable after 12 weeks of device storage,suggesting long-lasting effects of Na diffusion.Our results not only point to a potential avenue to increase PSM performance but also highlight the possibility of unabated Na diffusion throughout a module's lifetime,especially if accelerated by the electric field and elevated temperatures achievable during device operation.

Efficient light harvesting from flexible perovskite solar cells under indoor white light-emitting diode illumination

This is the first report of an investigation on flexible perovskite solar cells for artificial light harvesting by using a white light-emitting diode （LED） lamp as a light source at 200 and 400 Ix, values typically found in indoor environments. Flexible cells were developed using either low-temperature sol-gel or atomic- layer-deposited compact layers over conducting polyethylene terephthalate （PET） substrates, together with ultraviolet （UV）-irradiated nanoparticle TiO2 scaffolds, a CH3NHBPbI3xClx perovskite semiconductor, and a spiro-MeOTAD hole transport layer. By guaranteeing high-quality carrier blocking （via the 10-40 nm-thick com- pact layer） and injection （via the nanocrystalline scaffold and perovskite layers） behavior, maximum power conversion efficiencies （PCE） and power densities of 10.8% and 7.2 pW-cm-2, respectively, at 200 lx, and 12.1% and 16.0 -tW＇cm-2, respectively, at 400 lx were achieved. These values are the state-of-the-art, comparable to and even exceeding those of flexible dye-sensitized solar cells under LED lighting, and significantly greater than those for flexible amorphous silicon, which are currently the main flexible photovoltaic technologies commercially considered for indoor applications. Furthermore, there are significant margins of improvement for reaching the best levels of efficiency for rigid glass-based counterparts, which we found was a high of PCE -24% at 400 lx. With respect to rigid devices, flexibility brings the advantages of being low cost, lightweight, very thin, and COlfformal, which is especially important for seamless integration in indoor environments.