Structure Control,Optical Properties And Photovoltaic Performance Of Mesoscopic Solar Cells

Recently,novel mesoscopic solar cells based on mesoscopic scale inorganic or organic semiconductor materials and highly porous three-dimensional?3D?metal oxide semiconductor interpenetrating networks,such as dye-Sensitized Solar Cells?DSSCs?and perovskite solar cells?PSCs?,have attracted tremendously attention.Especially,the power conversion efficiency?PCE?of mesoscopic PSCs has been rapidly increased to over 22%,being comparable to silicon?Si?,cadmium telluride?CdTe?,and copper indium gallium diselenide?CIGS?solar cells,in a little over seven years.Mesoscopic solar cells are promising for a next generation highly efficient photovoltaic?PV?products due to their easy manufacturing processes and low manufacturing cost.Currently,both DSSC and PSC mesoscopic solar cells face some issues and challenges,including Fresnel reflection loss,limited absorption of active layers,and spectral mismatch,etc.Solving these problems will bring much development of mesoscopic solar cells,even breaking the theoretical efficiency of a solar cell made from a single p-n junction.Structure control and optimization of optical properties of DSSC and PSC mesoscopic solar cells have been systemically carried out in order to overcome Fresnel reflection loss,limited absorption of active layers,and spectral mismatch in these PV devices.The PV performance of mesoscopic solar cells is enhanced.The related physical mechanisms are explored.Detailed description of the research is listed as following:1.NaGd F₄:Eu³⁺/polymethyl methacrylate?PMMA?down conversion?DC?films were designed and fabricated in order to reduce the spectral mismatch in DSSCs and promote the PCE of DSSCs.Highly uniform,dispersive and luminescent Eu³⁺doped Na GdF₄ nanocrystals?NCs?were synthesized using hydrothermal method.DC layers consisting of PMMA doped with luminescent NaGdF₄:Eu³⁺were prepared and attached onto the back of a prefabricated TiO₂ anode to form a more efficient DSSC,compared with a device based on a pure TiO₂ electrode.The influences of both doped and undoped NaGdF₄ NC layers on the photovoltaic devices were compared and evaluated by the measurement of the device's incident-photon-to-current efficiency?IPCE?.An obvious increase in IPCE was observed when the DC layer was added in the device.As the down-converted photons can be reabsorbed within DSSCs to generate photocurrent,the DSSC with a 100 nm thick NaGd F₄:Eu³⁺DC-PMMA layer improved photoelectric conversion efficiency by 4.5%relative to the uncoated solar cell.2.Silica nanosphere based antireflection coatings?ARCs?were designed and fabricated in order to reduce Fresnel reflection loss in mesoscopic PSCs and promote the PCE of PSC devices.SiO₂ nanosphere based ARCs were deposited on the front glass surface of the as-prepared PSC solar cell by a sol-gel spin-coating method.The morphological and optical properties of the ARC films were tuned and optimized by changing the spin-coating speed.The effect of SiO₂ nanosphere based ARCs on the photovoltaic performance of perovskite solar cells is systematically investigated.The optimized SiO₂ nanosphere ARC coating on the glass substrate averagely increased the transmittance by about 3.8%in a broad wavelength range of 300-800 nm,therefore leading to a significant increase in the efficiency of the PSC device,demonstrating over 6.8%enhancement,compared with the reference device without SiO₂ nanosphere ARC.3.Composite film with luminescence conversion and antireflection dual functions were designed and fabricated in order to reduce the spectral mismatch and Fresnel reflection loss in mesoscopic PSCs and raise the PCE of solar cells.Highly uniform,dispersive,luminescent and up conversion?UC?and DC dual mode NaYF₄:Tm,Yb,Gd nanorods were synthesized by a hydrothermal method.The influence of the concentration of Gd³⁺on the size and the luminescent property of NaYF₄:Tm,Yb,Gd nanorods were investigated.The grown NaYF₄:Tm,Yb,Gd nanorods were used to prepare NaYF₄:Tm,Yb,Gd/SiO₂ dual function composite films on the front glass surface of the as-prepared PSC solar cell.The optimized dual function composite film concurrently modified the sunlight spectrum to better match the optical properties of solar cells and suppressed broadband reflectance in typical PSC solar cells,leading to a significant increase in the efficiency of the PSC device,demonstrating over 8.0%enhancement,compared with the reference device without NaYF₄:Tm,Yb,Gd/SiO₂ composite film.The related PV performance enhancement mechanisms are explored.4.New-style and highly efficient plasmonic perovskite solar cells?PSCs?were designed and fabricated in order to overcome the limited absorption of active layers in mesoscopic PSCs and raise the PCE of solar cells.Highly uniform and dispersive Au@TiO₂ core-shell nanoparticles were synthesized using chemical method.The grown Au@TiO₂ core-shell nanoparticles were integrated into porous TiO₂ and/or perovskite semiconductor capping layers to form plasmonic PSC devices with different configurations.Optical,electrical and electronic effects from metal nanostructures on the device performance of PSCs were systematically investigated by a combined evaluation of surface morphologies of Au@TiO₂ modified porous TiO₂and perovskite capping films,photovoltaic characteristics,photocurrent behavior and steady-state photoluminescence?PL?.The addition of Au@TiO₂ NPs increased the rate of exciton generation and the probability of exciton dissociation,thereby enhancing the shot-circuit current density and the fill factor.Accordingly,when 80 nm sized Au@TiO₂ NPs were simultaneously incorporated into both mesoporous titania and perovskite capping layers in the devices,the power conversion efficiency?PCE?was improved from 12.59%to 18.24%,demonstrating over 44%enhancement,compared with the reference device without the metal NPs.The results offer a possible method to dramatically enhance the performance of mesoporous PSC devices by employing metal nanoparticles and provide further insight into the development of ideal plasmonic functionality for future optoelectronic systems.