Long-term stable perovskite solar cells prepared by doctor blade coating technology using bilayer structure and non-toxic solvent

The doctor blade coating technology for the perovskite solar cells (PSCs) is studied. The bilayer and triple-layer structures based on CsFAPb(IBr)3 and MAPbI3 layers were designed and fabricated by the doctor blade coating. The conventional highly toxic dimethylformamide (DMF) used in the precursors are replaced by the mixtures of gamma-butyrolactone (GBL) and dimethyl sulfoxide (DMSO). Single cation and mixed-cation perovskite layer with different stacks are also compared. It is found that the as-prepared single cation perovskite (MAPbI3) PSCs have better photovoltaic performance but worse lifetime than those of the mixed-cation perovskite (CsFAPb(IBr)3) PSCs. Additionally, the bi-layer structure PSC has a brighter and smoother surface, higher quantum efficiency, and higher crystallinity. Those factors concerning the MAPbI3/CsFAPb(IBr)3(upper/lower) solar cell to have superior properties and better lifetime under the elevated temperature and humidity than that of the CsFAPb(IBr)3/MAPbI3(upper/lower) solar cell. Moreover, when the MAPbI3 is used as the capping layer of the CsFAPb(IBr)3/MAPbI3 bilayer PCS, its photovoltaic performance is better. Secondary ion mass spectroscopy indicates that MAPbI3 capping layer has better ability to dissolve the bottom layers than that of CsFAPb(IBr)3 due to the reduction of inter-diffusion of molecules and smooth surface during lifetime test. Finally, the MAPbI3/CsFAPb(IBr)3 bilayer device shows the best initial power conversion efficiency (PCE), Voc, and Jsc of 15.4%, 1.01 V, and 20.7 mA/cm2 respectively. The encapsulated PSC keeps 92% of original PCE under ambient environment at room temperature and relative humidity of 40% after 1000 h.