The Study Of Low Cost Fabrication Of High Efficiency Perovskite Solar Cells

Organic-inorganic hybrid halide perovskite solar cells(PSCs)have attracted enormous attention due to its excellent photoelectric properties and simple fabrication methods since it was first reported in 2009.The power conversion efficiency(PCE)of PSCs has soared from 3.8%to 25.5%.These typical organic-inorganic hybrid halide perovskites possess excellent properties such as high absorption coefficient,suitable band gap,high carrier mobility,long carrier diffusion length,ambipolar charge transport capability and low exciton binding energy.PSCs are considered to be the most likely to replace silicon solar cells as the next generation of commercial thin-film solar cells.However,high efficiency PSCs are based on complicated multiple layer structures with a perovskite active layer sandwiched between an electron transport layer(ETL)and a hole transport layer(HTL).The complex preparation processes and the high cost of ETL and/or HTL are not compatible with the mass production of efficient PSCs in a cost-effective manner.Though both ETL and HTL have been proved to be vital to achieve high efficiency PSCs,they are also considered to be one of the sources of instability in PSCs due to the chemical or the ultraviolet photocatalytic reactions at the interface between the perovskite and ETL/HTL.We start with the charge transport layer(CTL)and reduce the manufacturing cost of PSCs by simplifying the device structure.The main content of this thesis includes the following four aspects:The research background and significance of solar cells are briefly introduced followed by the classification and the working principle of solar cells.After introducing the research status of PSCs and the perovskite materials and the structure of PSCs commonly used,the challenges in the commercialization of PSCs and the aim and innovation of this thesis are presented.When using diluted PEDOT:PSS as HTL,its transmittance and conductivity have been improved,and the defect state density between the HTL and perovskite has also been significantly reduced.Then the charge extraction and transfer across the interface is more efficient,resulting in enhanced short-circuit current(Jsc).The work function of the PEDOT:PSS after diluting matched better with that of the perovskite,leading to the improved open circuit voltage(VOC).The experimental results show that the highest PCE can be achieved when the volume ratio of water and PEDOT:PSS solution is 10:1.The highest PCE of 17.85%of device with diluted PEDOT:PSS is drastically contrast to the one with undiluted PEDOT:PSS(The PCE is 16.04%).Thus the use of diluted PEDOT:PSS as HTL can not only significantly improve the performance of PSCs,but also can greatly reduce the cost of devices via less HTL.Band bending at ITO-Perovskite interface was proposed to fabricate highly efficient PSCs without ETL or HTL in this study.Direct depositing perovskite(MAPbI3-xClx)film on clean ITO results in downward shift of the band of the perovskite by about 170 meV at the ITO-Perovskite interface,preventing holes from recombining with electrons collected in the ITO.The device without dedicated ETL or any modifications achieves a PCE of 17.42%.The band bending direction changes when a Sn—Pb mixed narrow band gap(1.21 eV)perovskite((FASnI3)o.6(MAPbI3)o.4)is used to replace MAPbI3-xClx.An upward band shift of about 110 meV is observed at the ITO-Perovskite interface,facilitating hole extraction while blocking electron transfer from the perovskite to ITO.PSCs are made by this narrow band gap Sn-Pb mixed perovskite achieves a PCE of 18.31%.Thus,band bending is proved to be an effective way to eliminate charge transport layers in PSCs.Band bending at an ITO-Perovskite interface was used to eliminate the charge transfer layer between ITO and perovskite,which simplifies the device structure and further reduces the manufacturing cost.Inspired by the above results of removal ETL or HTL between substrate and the perovskite by controlling the band bending direction,the charge transport layer between the back electrode and the perovskite can also be eliminated.The device structure is further simplified without ETL and HTL.We have constructed the simplest PSC structure of ITO/Perovskite/Metal.When metal Ag is used as the electrode,a PCE of 4.4%is obtained.Due to the chemical reaction between Ag and the halogen element in the perovskite,the performance of the device rapidly degrades.When changed to metal Sn,the PCE is improved to 5.09%with better stability.Although the PCE and stability of the device without ETL and HTL needs to be further improved,the simplest structure can bring the fabrication cost extremely low.In summary,this thesis starts with diluted PEDOT:PSS as HTL,which not only improves the performance of the device,but also reduces the amount of HTL and then the production cost of PSCs.Then,the energy band bending between ITO and perovskite interface is used to eliminate the charge transfer layer between ITO and perovskite,which further reduces the manufacturing cost.Finally,we try the removal both ETL and HTL to make the device structure the simplest and the manufacturing cost lowest.This thesis simplifies the device structure through the band bending,which provides a new idea and a direction for low-cost preparation of high-efficiency PSCs.