Lanthanide Stabilized All-Inorganic CsPbI2Br Perovskite Solar Cells with Superior Thermal Resistance

The stability of perovskite solar cells, especially at high temperature (85 degrees C) conditions, is one of the most critical aspects to advance practical application. All-inorganic perovskites, by substituting the volatile organic compounds with cesium, have exhibited a promising thermal resistance and energy conversion potentials. However, the thermal stability of the all-inorganic perovskite solar cells is strongly related to the phase transition of the perovskite as well as the thermal resistance of each charge transport and collection layer. Herein, we incorporated Eu(Ac)(3) into the perovskite precursor to fabricate photoactive gamma-CsPbI2Br. The Eu3+ ions can associate with the negatively charged halide plumbates in the solution and accumulate at the grain boundaries in the as-achieved thin films, effectively reducing the nonradiative recombination centers and stabilizing the gamma-CsPbI2Br with moderate grain size. A champion efficiency above 12% in an inverted device architecture can be achieved. In the presence of Eu' ions, the phase transition of the gamma-CsPbI2Br to nonperovskite is significantly mitigated and can be reversibly restored via thermal repairing. Moreover, we thermally treat the electron transport [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) layer prior to the device completion to induce nanomorphology reorientation and replace the reactive Ag electrode by inert Cu to prevent electrode corrosion by diffusive halide ions from the perovskite. As a result, the thermal (at 85 degrees C, time to 80% of the initial efficiency or t(80) approximate to 200 h) and moisture (relative humidity or RH = 40%, t(80) > 500 h) stability of the all-inorganic CsPbI2Br solar cells can be remarkably enhanced.