低能氨离子/基团扩散对铟锡氧化物薄膜电学性质的影响规律

Influence of low-energy ammonia ion/group diffusion onelectrical properties of indium tin oxide film

有机-无机杂化甲氨铅碘类钙钛矿太阳能电池在制备及使用过程中,甲氨铅碘层中的甲基铵离子易分解为甲基离子/基团和氨离子/基团,其中氨离子/基团可以扩散进入铟锡氧化物(indium tin oxide,ITO)透明电极层,并影响ITO的电学性质.本文通过低能氨离子束与ITO薄膜表面相互作用,研究低能氨离子/基团在ITO薄膜表面扩散过程,及其对ITO薄膜电学性质的影响规律.研究结果表明,低能氨离子/基团在ITO薄膜表面扩散过程中,主要与ITO晶格中的O元素结合形成In/Sn-O-N键.ITO不同晶面的O元素含量不同,低能氨离子/基团能够在无择优ITO薄膜表面的各个晶面进行扩散,因此将严重影响其电学性质,导致无择优ITO薄膜电阻率增加约6个数量级.但(100)择优取向ITO薄膜的主晶面为(100)晶面,最外层由In/Sn元素构成,不含O元素.因此(100)择优取向ITO薄膜能够有效地抑制低能氨离子/基团扩散,并保持原始电学性质.最终,(100)择优取向ITO薄膜有望成为理想的有机-无机杂化甲氨铅碘类钙钛矿太阳能电池用透明电极层材料.

In the case of methylammonium lead halide(MAPbH3)perovskite solar cells,the indium tin oxide(ITO)film has been widely used as the transparent electrode.In the preparation process and service process of MAPbH3 perovskite solar cells,the MAPbH3 perovskite layer can decompose into the methyl,amino,methylammonium,halide ion/group,etc.Thus,the diffusion of ammonia ion/group into ITO film is inevitable,which can seriously deteriorate the electrical property of ITO transparent electrode.In this study,the ITO films with and without(100)preferred orientation are bombarded by a low-energy ammonia(NHx)ion beam.After the bombardment,the electrical properties of ITO film without preferred orientation are deteriorated seriously,especially for carrier concentration,which is deteriorated down to an extent of about 5-6 orders of magnitude.The bombardment of low-energy NHx ion/group has little influence on the electrical properties of ITO film with(100)preferred orientation.Such phenomena can be explained by the following reasons.Based on XPS measurement results,the low-energy NHx ion/group diffuses into the ITO film surface after the bombardment.In the diffusion process,the low-energy NHx ion/group is mainly bonded with O in ITO lattice,which results in the formation of In/Sn—O—N bond.Based on the crystal structure of ITO,the(100)lattice of ITO consists of=1.76 J/m^2.While the(110)and(111)lattices of ITO consist of In/Sn/O,in which the O atom percent on(110)and(111)lattices are 56 at.%and are 1.07 and 0.89 J/m^2,respectively.Combining the XPS measurement results and crystal structure of ITO,it can be understood that in the diffusion process of low-energy NHx ion/group into ITO film without preferred orientation,lots of In/Sn-O-N bonds are formed in the ITO lattices,which are rich in O and have lower surface energyγ.Then,after the low-energy NHx ion/group bombardment,the electrical properties of ITO film without preferred orientation are deteriorated seriously.On the contrary,because of the absence of O and the highest surface energyγ,it is hard for the low-energy NHx ion/group to diffuse into ITO(100)lattice.Then,after the low-energy NHx ion/group bombardment,the electrical properties of ITO film with(100)preferred orientation have little change.With all results,the ITO film with(100)preferred orientation can be an ideal candidate for transparent electrode in MAPbH3 perovskite solar cells.