Study On The Hole-transporting Materials For Organic–inorganic Lead Halide Perovskite Solar Cells

Organic-inorganic lead halide perovskite solar cell?PSC?technology is one of the research hotspots in the photovoltaic field,on primary account of its high cost-effectiveness.During the past few years,PSC has achieved tremendous improvements.Since the seminal work reported in 2009,the power conversion efficiency?PCE?of PSCs has increased at an unexpected rate from 3.8%to 22.7%over the past 8 years.Hole-transporting material?HTM?,as a momentous part of PSC,has profound effects on the ultimate power output of a PSC.2,2',7,7'-tetrakis?N,N-p-dimethoxyphenylamino?-9,9'-spiro-bifluorene?Spiro-OMeTAD?is the most commonly used HTM in high efficient PSCs.However,it is expensive due to its complexity of synthesis and difficulty of purification.Moreover,Spiro-OMeTAD needs to be doped with relatively expensive cobalt complex to improve its hole mobility.Thereby,the development of low-cost and efficient HTM is one of the crucial driving forces to improve the economical efficiency of PSCs,which is attracting enormous scientific interest.Here we focused on this topic and did the following research works:1.For the first time,we have employed the low-cost inorganic salt FeCl₃ as a dopant for Spiro-OMeTAD and compared its performance with the traditional cobalt complex FK209dopant.Experiments proved that FeCl₃ can effectively oxidize Spiro-OMeTAD,decrease the HOMO energy level and improve the hole transporting properties of Spiro-OMeTAD,which facilitates the hole injection process and suppresses the charge recombination at the interface.Through carefully optimizing the dopant concentration,solar cells with 80%FeCl₃ doped Spiro-OMeTAD achieve over 17%power conversion efficiency with an open circuit voltage of 1.11 V,which is better than that of devices with FK209 as dopant.Moreover,FeCl₃ doped devices show good stability.2.Based on the widely employed unit dithienopyrrole in dye-sensitized solar cell,we have designed and prepared two small-organic hole-transporting materials:Me-TPA-DTP-C6,MeO-TPA-DTP-C6.The photoelectric properties of these two materials have been characterized.Measurements have shown that the HOMO energy levels of these two molecules are-5.35 eV and-5.25 eV,respectively,which feature suitable energy level alignment with perovskite layer.Due to the efficient hole extraction,the photoluminescence lifetime was shorted from 200.4 ns of perovskite film to 61.4 ns and 23.2 ns for perovskite coated with these two HTMs,respectively.Over 16%PCE of a PSC was obtained through optimization based on these two HTMs.Our work demonstrates the good potential of using these two molecules as hole transporting materials in PSCs.