Stable NiOx-based inverted perovskite solar cells achieved by passivation of multifunctional star polymer

Perovskite materials have excellent photoelectric properties and are a hot spot in international research. How-ever, there are deep/shallow energy level traps in the grain boundaries (GBs)/surface of perovskite thin films, which affect the optoelectronic performance of perovskite solar cells (PSCs). Here, we design and synthesize a three-dimensional star-shaped polymer with various groups to regulate the light-absorbing layer of perovskite. The eight branched chains of multifunctional star polymer are rich in C--O, N = N, N = O, and -CF3 functional groups, which are used to passivate uncoordinated lead ions and to immobilize methylamine, formamidine cations on the GBs/surface of perovskite films. Simultaneous passivation of deep-level defects and suppression the appearance of shallow-level defects on the perovskite surface/GBs, thereby greatly improving the opto-electronic performance of PSCs. Compared with the efficiency of 22.38 % of the reference device, the efficiency of the multifunctional star polymer incorporated inverted device reaches 24.03 %. Moreover, the multifunctional star-shaped polymer modified inverted-encapsulation device also exhibits excellent operational stability, main-taining 80 % of the initial efficiency for more than 5500 h.