铯掺杂提升反梯度结构二维(CMA)_(2)MA_(8)Pb_(9)I_(28)钙钛矿薄膜及太阳电池的性能

Cesium doping for improving performance of inverse-graded 2D(CMA)_(2)MA_(8)Pb_(9)I_(28)perovskite film and solar cells

相对于3D钙钛矿材料,二维(2D)有机-无机杂化钙钛矿材料具有更好的稳定性.然而由于载流子输运性差,2D钙钛矿太阳电池效率较低.为了提高2D钙钛矿太阳电池的效率,制备了铯掺杂的具有反梯度结构的二维(CMA)_(2)MA_(8)Pb_(9)I_(28)薄膜.研究结果发现:CsI掺杂能够改善(CMA)_(2)MA_(8)Pb_(9)I_(28)薄膜的形貌、增加晶粒尺寸、降低缺陷态密度,并且提高了(CMA)2MA8Pb9I28钙钛矿薄膜的热稳定性.最后,CsI掺杂浓度为10%时制备(CMA)_(2)MA_(8)Pb_(9)I_(28)钙钛矿太阳电池效率最高,达到了14.67%,相对于未掺杂的电池效率(10.06%)提高了45.8%.

Compared with three-dimensional(3D)perovskites,two-dimensional(2D)perovskites have excellent environmental stability.However,the efficiency of 2D perovskite solar cells is still lower than that of their 3D counterparts owing to the poor carrier transport.In order to improve the efficiency of 2D perovskite solar cells,the cesium(Cs)doping 2D(CMA)_(2)MA_(8)Pb_(9)I_(28)films with an inverse gradient structure(small n quantum well(QW)located at the surface and large n QW at the bottom)are prepared.The inverse gradient QW structure has the advantages of being more moisture-resistant(small n QW protects the vulnerable large n QW from being attacked by water molecules)and favoring self-driven charge transport(type-II band alignment between different phases).The results show that the quality and thermal stability of 2D(CMA)_(2)MA_(8)Pb_(9)I_(28)film can be effectively improved by using Cs doping.The SEM images show that the film grains become larger,and the surface is smoother and more compact with CsI content increasing.When CsI increases to 15%,the surface becomes coarse.From the XRD,it can be seen that the crystallinity of perovskite is improved with CsI doping,and it reaches saturation when CsI content increases to 10%.The PL intensity of the film with 5%CsI is higher than the others’,implying a relatively low non-radiative recombination loss and low defect state in that film.Therefore,the minority carrier average lifetime of film doped with 5%CsI is the longest.The absorption is almost unchanged when CsI is doped.The thermal stability of film can be effectively improved when CsI exceeds 10%.Considering the SEM images,crystallinity,PL intensity,light absorption and thermal stability of perovskite,the optimized CsI doped concentration is 10%in our work.Finally,the highest efficiency of(CMA)(CMA)_(2)MA_(8)Pb_(9)I_(28)perovskite solar cells doped with 10%CsI content reaches to 14.67%,with a short-circuit current density(JSC)of 23.16 mA/cm^(2),an open-circuit voltage(Voc)of 1.05 V and a fill factor(FF)of 60.75%.The efficiency of the undoped cells is 10.06%,which is lower than that of CsI doped cells(10%).Therefore,CsI doping is an effective method to further improve the efficiency and thermal stability of 2D perovskite solar cells.