Preparation And Photoelectric Performance Of High Efficient And Low-temperature Perovskite Solar Cells

In recent years,perovskite solar cells(PSCs)have been one of the most promising new solar cells due to their novel properties such as high absorption,simple fabrication process as well as high power conversion efficiency.Following the first reported efficiency of 3.8%in 2009,a certificated power conversion efficiency as high as 22.7%has been achieved in 2017.However,most high efficient PSCs are usually used high-temperature processed TiO2 as electron transfer layer and annealed high-crystallinity perovskite absorber layer.In this work,aiming at dreasing techonology temperature and improving photoelectric conversion efficiency,we focus on the study of perovskite absorber layer.Firstly,we report a high-efficiency methylammonium(MA)and Cs co-alloying formamidinium(FA)triple cation perovskite based ZnO PSCs via delicate control of the cation compositions and annealing temperature.And then we further explore the preparation of room-temperature processed perovskite layer to achieve the low-temperature preparation of total device.The specific details are as follows:(1)A high-efficiency methylammonium(MA)and Cs co-alloying formamidinium(FA)triple cation perovskite is prepared based ZnO electron transfer layer via delicate control of the cation compositions and annealing temperature.By virtue of structural,morphological,spectral and electrochemical characterizations and analysis,we find that incorporation of MA and Cs into FA perovskite enables to form high-crystallinity black phase perovskite with reduced surface roughness,inhibit charge recombination and promote electron transfer at the ZnO/perovskite/Spiro-OMeTAD interfaces,and hence improve the cell FF and Jsc.As a result,the ZnO PSC based on MA0.1FA0.75Cs0.15PbI3 being annealed at 110℃ achieves a PCE as high as 20.09%,exceeding the previous highest efficiency recorded for ZnO ETL based PSCs.The optimized MA0.1FA0.75Cs0.15PbI3 is demonstrated to possess excellent reproducibility and long-term cell durability under ambient condition within 1000h.Particularly,incorporation of a small portion of Br into the triple cation perovskite i.e.MA0.1FA0.75Cs0.15PbI2.9Br0.1 leads to a further enhancement in PCE up to 20.44%,comparable to the best-performing MA and Cs-containing FA-based lead halide TiO2 PSCs.(2)By exploring the perovskite layer and photovoltaic performance with different content of Br at room temperature,we find that Br plays a vital important role in inducing complete formation of the black perovskite phase at room temperature.At 35-40 ℃(summer),upon addition of 20/3mol%Br,the yellow-phase completely vanishes.And the best PCE of MA0.1FA0.75Cs0.15PbI2.8Br0.2(Br-0.2)is 19.59%,which is close to the best PCE of annealed perovskite.More importantly,the exist of Br is benefit for not only photoelectricity performance but also the humidity stability.When the room temperature decreases to 20-25 ℃(winter),the Br-0.2 perovskite film does not yield the total black phase,and the best PCE of Br-0.2 decreases to 15.15%.Upon addition of Br from 0.2 to 0.5,the yellow phase were disappears,and the best PCE of 17.53%is obtained by Br-0.5.Thus,pure photoactive black phase can still be formed by increasing Br content when the room temperature decreases,which further demonstrate Br can facilitate forming pure perovskite phase at room temperature.