Effect Of Conjugate Bridge Of Triphenylamine Hole Transport Materials On The Performance Of Inverted Perovskite Solar Cells

Perovskite materials have attracted widespread attention due to their unique photoelectric properties(direct band gap,high optical absorption coefficient,high carrier mobility),simple synthesis method,and low-cost solution-process.Perovskite solar cells are considered to be one of the most promising next generation solar cells with certification efficiency of 24.2%.Hole transport materials have an important effect on the power conversion efficiency of perovskite solar cells.At present,PTAA(used in the inverted p-i-n structure)and Spiro-OMeTAD(used in the direct n-i-p structure)are widely used as hole transport materials in high efficiency perovskite solar cells.However,PTAA and Spiro-OMeTAD have high cost,poor conductivity and need to be doped with additive to improve conductivity.The use of dopant not only reduces the stability of the device,but also further increases the cost of fabrication.Therefore,the design and development of low-cost and efficient non-doped hole transport materials is of great significance to improve the efficiency and stability of perovskite solar cells and to reduce the cost of device fabrication.In this paper,ten different small molecule triphenylamine hole transport materials with different conjugate bridge structures are explored in the inverted planar perovskite solar cells and their influence on the performance and stability of the device were investigated.Detailed research contents are as follows:First,the effect of three triphenylamine organic small molecule hole transport materials(TZ1,TZ2 and TZ3)on the performance of inverted planar perovskite solar cells was studied.These three hole transport materials and the inverted devices based on them were characterized by means of XRD,SEM,UV-vis,PL,TRPL,AFM,C-AFM and EIS.The results show that the different structures of the conjugate bridge have a different effect on the performance of devices in direct and inverted structures.Triphenylamine materials with highly conjugated bridges are suitable for the direct cells.Contrary,triphenylamine materials with deep HOMO levels are suitable for the inverted cells.TZ3 with DTTT as conjugate bridge has a higher work function and higher hole extraction ability.A power conversion efficiency of 16.33%(Voc=0.97 V,Jsc=22.16 mA/cm~2,FF=76.0%)is obtained in the inverted device.This result exceeds the performance of device using PEDOT:PSS as hole transport material(Voc=0.91 V,Jsc=22.10mA/cm~2,FF=76.0%,PCE=15.28%).Second,the effect of four organic small molecule hole transport materials(M107,M108,M109 and M110)with phenyl and its derivatives as conjugate bridge on the performance of inverted planar perovskite solar cells was studied.These hole transport materials and the corresponding inverted devices were characterized by means of XRD,SEM,UV-vis,PL,TRPL,AFM,C-AFM and EIS.The results show that the introduction of conjugate bridge affects the HOMO levels and hole mobility of M108,M109 and M110 triphenylamine molecules.The improvement of device performance is attributable to the enhancement of hole mobility,HTMs/perovskite interface and conductivity of thin films.Among them,the inverted device based on M109 as the hole transport layer achieves 15.88%power conversion efficiency,yielding a result that is close to the inverted device with PEDOT:PSS as the hole transport layer(PCE=15.28%).The stability tests show that the inverted devices based on the four organic small molecule hole transport materials have higher stability than PEDOT:PSS.Third,the effect of three triphenylamine organic small molecule hole transport materials(H111,H112 and H113)on the performance of inverted planar perovskite solar cells was studied.These three hole transport materials and relevant inverted devices were characterized by means of XRD,SEM,UV-vis,PL,TRPL,AFM and EIS.The results show that the conjugate bridge has little effect on the HOMO level.Compared with the inverted cell with PEDOT:PSS as the hole transport layer,the inverted cells based on H111,H112 and H113 have lower performance.However,the stability test shows that inverted device based on these three hole transport materials has higher stability than that of PEDOT:PSS.