Study On Spectral Regulation And Performance Of Perovskite Solar Cells

As an emerging photovoltaic material,the organic-inorganic metal halide perovskite material with ABX₃ structure has received extensive attention from global academic and industry communities due to its high light absorption coefficient,small exciton binding energy,tunable bandgap and solution processing method,which is regarded as one of the most prospective photoelectric materials for future applications.Its power conversion efficiency（PCE）has soared from 3.8%to 26.1%,demonstrating the efficiencies required to fulfill technical and economic competitiveness,comparable to that of commercial silicon-based solar cells.However,limited by the bandgap width and spectral mismatch,the conventional MAPbI₃ perovskite solar cells（PSCs）can only absorb light in the range of 300-800 nm in the total solar radiation spectrum,and its light-capturing ability is substantially weakened due to the rapid decay of the extinction coefficient in the range of 600-800 nm.And it is incapable of utilizing the spectra of the near infrared（NIR）and infrared（IR）regions,resulting in a large energy loss,thus there is still a great deal of room for improvement with respect to the Shockley-Queisser limit.In addition,due to the photocatalytic activity of the inorganic metal oxide interfacial layer and the photoinstability of lead iodide,the photovoltaic performance of the PSCs device will decay rapidly after prolonged irradiation under the higher energy ultraviolet（UV）light,which seriously hampers its further commercialization.In view of the above problems,this paper mainly focuses on low solar spectrum utilization and poor UV stability faced by PSCs from the perspective of broadening the spectral response range of the device to improve efficiency and enhance stability.Through the introduction of novel triplet-triplet annihilation（TTA）photon up-conversion technology and down-conversion multifunctional capsules into the PSCs for spectral regulation to achieve high-efficiency and stable PSCs.The main research work is as follows:1)The photovoltaic materials will only respond to solar energy that matches the intrinsic bandgap E_g,and those incident photons with energies smaller than the bandgap will be lost due to unavailability,resulting in underutilization of the solar spectra.Herein,the TTA up-conversion technology,which can still exhibit efficient energy conversion under low photon flux conditions,is introduced into PSCs.The combination of annihilator rubrene and emitter dibenzotetraphenylperiflanthene（DBP）can convert long-wavelength NIR light into short-wavelength visible light,and the converted visible light is reabsorbed by the MAPbI₃ perovskite photoactive layer,which enhances the spectral utilization.Attributed to the TTA up-conversion effect and more suitable energy level alignment,the fabricated PSCs based on MAPbI₃ acquires a PCE of 20.18%accompanied by significant enhancements in photovoltaic parameters such as open-circuit voltage and short circuit current density.Furthermore,the unencapsulated device can maintain more than 80%of its initial PCE after 14 days of storage under ambient conditions of 50-70%relative humidity.2)In consideration of the weak absorption capacity in the NIR region of 750-800nm when MAPbI₃ perovskite is used as a single sensitizer in the second chapter,copper-octafluorophthalocyanine（F₈Cu Pc）exhibits intense absorption in the NIR region,which is employed as a cosensitizer to minimize the sub-bandgap photon transmission loss and thus further broaden the NIR response of PSCs.Meanwhile,the addition of F₈Cu Pc cosensitizer not only passivates the surface and grain boundary defects of perovskite,but also forms a hydrophobic and thermotolerant barrier,which lays a solid foundation for the excellent long-term stability of devices.Based on the firm hydrogen bonding interaction（F···H-N between F₈Cu Pc and MA⁺）,cation-πinteraction（MA⁺with aromatic rubrene molecule）,and the hydrophobic characteristic of additives enable the dually-sensitized inverted PSCs based on MAPbI₃ and Cs_0.05(FA_0.83MA_0.17)_0.95Pb(Br_0.17I_0.83)₃ photoactive absorbers to attain champion PCEs of 20.83%and 21.51%,respectively.In addition,the unencapsulated dually-sensitized devices possess superior humidity and thermal stability,and the corresponding PSCs can maintain nearly 80%of the original PCE exposed to air with 50-70%relative humidity over 1100 h and nitrogen atmosphere at 85°C for 300 h.3)The use of UV filters can ameliorate UV light tolerance of the PSCs device,but this will increase the extra cost and block the UV part of the solar spectra from entering the perovskite photoactive layer to be effectively absorbed and utilized,thus leading to a reduction in PCE.In order to improve the utilization rate of UV light in PSCs,further inhibit its degradation under UV irradiation,and achieve a win-win situation in terms of device efficiency and stability.We introduce a down-conversion multifunctional capsule layer consisting of zeolitic imidazolate framework-8（ZIF-8）encapsulant and formamidinium iodide（FAI）between the interface of the tin oxide and lead iodide（Pb I₂）layer,and the PCE of the device fabricated by two-step sequential deposition method is increased to 24.08%.The ameliorative device performance can be attributed on the one hand to the conversion of incident UV light into visible light,which is further absorbed and reused by the perovskite layer,generating more photogenerated carriers,and on the other hand to the morphology control of the Pb I₂layer and the reduction of carrier nonradiative recombination inside the device.Furthermore,the constituent FAI of the perovskite precursor in the multifunctional capsule can convert into the crystal nuclei of perovskite by reacting with Pb I₂ first,thereby promoting further perovskite crystallization growth.Based on the down-conversion effect,the modified PSCs devices exhibit decent UV tolerance,retaining83%of the initial efficiency under 365 nm UV illumination for 300 h.