Study On Carbon Electrode Of Mesoscopic Perovskite Solar Cells

With the increasing serious energy crisis and environmental pollution problems,the development of renewable clean energy has become a major subject.Under these circumstances,a low-cost and high efficient solar cell attracts great attention of researchers all over the world.In recent years,organic/inorganic hybrid metal halides perovskites,such as CH₃NH₃PbI₃,are widely used in photovoltaic field due to their high absorption coefficient,high carrier mobility and long carrier diffusion distance.At present,the power conversion efficiency（PCE）of perovskite solar cell（PSC）as light absorbing materials has reached 22.7%.However,this perovskite solar cell and its commercial applications are still limited by some issues such as stability,cost and large-scale manufacture.The printable TiO₂/ZrO₂/C triple-layer mesoscopic perovskite solar cell（MPSC）was developed,in which the cheap carbon electrode replaced the expensive gold electrode used in conventional devices.The device structure is simpler without hole transport materials,and the device fabrication is completed using the screen-printed process.Meanwhile,unpackaged devices are stable for 1000 hours in air under continuous illumination by adding amino acid salts into perovskite materials and the certified efficiency of the cell has reached12.84%in 2013.Therefore,the triple-layer perovskite solar cells have the advantages of low cost,easy preparation,high stability,which is suitable for industrial production,exhibiting great commercial potential.However,the efficiency of the cells is lower compared with that of conventional structural devices.As a key role,the work function,conductivity,surface property and specific surface area of the carbon electrode affect the filling of perovskite precursor solution,carrier extraction and collection,which have an important impact on the photoelectric performance of cells.Therefore,the carbon electrode of the printable TiO₂/ZrO₂/C triple-layer MPSC is studied.The main work is listed as following:（1）Carbon electrode was doped by boron atom to improve the work function,so the energy level is better matched to perovskite and thereby reducing the electron hole recombination.At the same time,the conductivity of graphite was improved due to catalytic graphitization effect of boron.Together with the merit of both high work function and conductivity,the efficiency of carbon-based hole-conductor-free MPSC was increased from 12.4%for the normal carbon based cells to 13.6%for the boron doped cells with an enhanced open-circuit voltage and fill factor.（2）The ultrathin graphite with high specific surface area was used to regulate the internal channel structure of the carbon electrode.Ultrathin graphite prepared by mechanical ball milling has a good conductivity,which was then applied in MPSC to improve the specific surface area of carbon electrode without sacrificing the conductivity,which accelerated the penetration of perovskite precursor solution and increase the contact area with perovskite.As a result,the PCE of MPSC has been significantly increased from12.63%to 14.07%with an improved fill factor from 0.62 to 0.68.（3）To solve the recombination in carbon electrode/perovskite interface,the inorganic hole transport material CuCrO₂ was used to encapsulate carbon to block some electrons generated from perovskite to be injected into carbon electrodes.Carbon black enwrapped with CuCrO₂ was prepared by hydrothermal synthesis.The composite was stable under400°C,which was suitable for high temperature sintering process of carbon film.Meanwhile,the size of CuCrO₂ was smaller,which helped to wrap nanosized carbon black particles.Then,the effect of CuCrO₂ modified carbon electrode on the performance of the cells was investigated.The results showed that the PCE of the device was 12.25%,which needed to be further improved by optimizing the enwrapping process.（4）Mesocarbon microbeads（MCMB）were used in carbon electrode instead of graphite.Morphology and growth of perovskite on MCMB were investigated.It is found that perovskite on the surface of MCMB exhibited a continuous phase distribution,rather than a discontinuous phase distribution on the surface of graphite.The steady-state photoluminescence and time-resolved photoluminescence were carried out to study the charge extraction ability of the MCMB and graphite in contact with the perovskite,respectively.Then,the influence of MCMB on the performance of MPSC was investigated.To optimize the performance of the device,three different compound carbon electrode structures were designed,and the maximum efficiency reached 14.35%.