Up-conversion (UC) is a promising approach to utilize sub-band-gap photons for solar cells (SCs). Due to the non-linear nature of UC, the optimal excitation power regimes between the solar cell semiconductor and the UC material correspond to a difference in solar concentration of more than an order of magnitude. This difference can be bridged with integrated optics by concentrating the photons transmitted through the solar cell to increase the power density and maximize the intensity of UC luminescence. To realize this, dielectric-filled compound parabolic concentrators (CPCs) were used as integrated optics on the rear side of a planar bifacial silicon solar cell together with a 25% Er3+ doped hexagonal sodium yttrium fluoride (β-NaYF4:Er) UC phosphor. An efficiency increase of 32% from 0.123% to 0.163% under sub-band-gap illumination is quantified by means of the first ever reported I-V characteristics for an up-conversion solar cell (UC-SC) based on c-Si. An enhancement in external quantum efficiency (EQE) is obtained from 1.33% for the non-concentrating reference UC-SC to 1.80% for a solar cell with integrated optics for an excitation at 1523 nm with an irradiance of 0.024 W/cm2, corresponding to a normalized EQE of 0.75 W/cm2. This demonstrates that CPCs are suitable for UC-SC as they increase the concentration in the forwards direction, while maintaining high collection efficiency of the UC emission in the reverse direction. In addition, such an approach enables the optimization of the solar concentration on the UC phosphor independently from the concentration required for the solar cell

The initial stages of photo‐degradation of CH3NH3PbI3 (MAPbI3) thin films prior to any significant change in light absorption are studied in experiments with independent control of sample temperature and intensity of concentrated sunlight from 50 to 500 suns. Photo‐stability of the MAPbI3 film is revealed to be extremely sensitive to the sample temperature. Under the combined action of light and heat (either by concentrated sunlight or by external heating), a strong reduction of the film photoluminescence (PL) without changes in the perovskite light absorption can be observed during the initial stages of degradation. In contrast, illumination of perovskite films (with intensity up to 500 suns) without heating (using chopped concentrated sunlight) induces considerable PL enhancement while the optical absorption spectrum remains unchanged. With accurate temperature control, aging under concentrated sunlight results in similar instability trends as that under 1 sun.

Development of novel nanoscale devices requires unique functional nanomaterials. Furthermore, chemical design of different nanoparticles in one unit is a complex task, particularly the application of self-assembly J-aggregates, which can substantially advance the nanomaterial's properties due to resonant delocalization of excitons. Here, we have demonstrated for the first time formation of resonantly coherent J-aggregates on carbon nanotubes with highly efficient energy transfer from the aggregates to the nanotubes. All energy of photons absorbed by the aggregates is conveyed to the nanotubes, completely quenching the Jband emission and photosensitizing the nanotubes. Overall, we discovered formation of two types of J-aggregates, where one type is related to self-assembly of cis-isomers on the nanotube surface and second type is associated to self-organizing trans-isomers into free J-aggregates without the nanotubes. Importantly, the J-aggregates on carbon nanotubes with strong energy transfer peaks of photoluminescence in near infrared range is of high interest for practical applications on biomedical imaging, nanoscale optoelectronic and nanophotonic devices.

No abstract