Research On Application Of Composite Transparent Electrodes In Semitransparent Perovskite Solar Cells

Over the last decade,halide perovskite solar cells（PSCs）have seen a rapid rise in efficiency from 3.8%to 25.6%,which predicts there will be more application scenarios for PSCs in the future.For example,semitransparent perovskite solar cells（ST-PSCs）have become an interesting research topic due to their increased potential for building-integrated photovoltaic,solar windscreen and wearable electronics.Perovskite has marvelous optical and electrical properties,such as high charge carrier mobility,high absorption coefficient and long carrier diffusion length.Therefore,it is widely used as a functional layer material for photoelectric conversion devices.And the most attractive advantage of perovskite is a direct and tunable band gap.This makes it possible to fabricate ST-PSCs where part of the sunlight can pass through the films and some of it is converted into electricity at the meanwhile.Transparent back electrode is necessary for the development of ST-PSCs,even though it always leads to a loss of photocurrent compared to opaque devices.An ideal transparent back contact requires high transparency,low sheet resistance and robust chemical stability.Some transparent conducting oxides（TCOs）,like fluorine-doped tin oxides（FTO）and indium tin oxides（ITO）,have been brought in optoelectronic devices as the transparent electrodes because of their outstanding optoelectronic properties and good reproducibility.However,TCOs electrodes are deposited by magnetron sputtering,which may damage the perovskite layer due to high temperatures（>300℃）.In addition,TCOs generally have less conductivity than metal electrodes.On the other hand,the transparency of metal electrodes is extremely sensitive to thickness.In general,when the thickness of metal film electrodes prepared by conventional vacuum vapor deposition method reaches 30 nm,they basically cease to be transparent.Dielectric-metal-dielectric（DMD）multilayer films have been studied to solve the contradiction between transparency and conductivity of metal thin film electrodes.The visible light transmittance and conductivity of the ultra-thin metal film can be significantly enhanced by sandwiching it between two conductive dielectric layers with highly refractive indices.Currently,transparent electrodes with DMD structures are mainly prepared by continuous vacuum vapor deposition.And the materials commonly used in dielectric layers include molybdenum oxide（Mo O₃）,tungsten oxide（WO₃）,zinc sulfide（Zn S）and vanadium oxide（V₂O₅）.In this thesis,we design a transparent conductive electrode with DMD structure,which we call it ZAZ transparent electrode.The electrode combines Zn O films prepared by Atomic Layer Deposition（ALD）technique and Ag film by vacuum evaporation.The thickness of the transparent dielectric layer and the metal layer are finely tuned,which gives the ZAZ electrode an average visible transmittance（AVT）of 70%and a sheet resistance less than 8Ω/□.The ZAZ electrode replaced the ultra-thin Ag electrode as the top electrode of ST-PSCs with n-i-p structure and enabled the device to achieve a significant transmittance enhancement and a PCE enhancement.Moreover,the ST-PSCs transmittance was further improved by sacrificing the absorption of part of the visible light through the rational regulation of the solution-based CH₃NH₃Pb I₃（MAPb I₃）film precursor solution.Finally,the semi-transparent device achieves an average visible light transmission rate of 19.6%with an efficiency of 10%.The results illustrate a strategy of novel structure designs for electrode to overcome the contradiction between efficiency and transparency of ST-PSCs.