Significantly Improved Efficiency and Stability of Pure Tin-Based Perovskite Solar Cells with Bifunctional Molecules

Tin-basedperovskite solar cells (TPSCs) have become one of themost prospective photovoltaic materials due to their remarkable optoelectronicproperties and relatively low toxicity. Nevertheless, the rapid crystallizationof perovskites and the easy oxidization of Sn2+ to Sn4+ make it challenging to fabricate efficient TPSCs. In thiswork, a piperazine iodide (PI) material with -NH- and-NH2 (+)- bifunctional groups issynthesized and introduced into the PEA(0.1)FA(0.9)SnI(3)-based precursor solution to tune the microstructure,charge transport, and stability of TPSCs. Compared with piperazine(PZ) containing only the -NH- group, the PI additivedisplays better effects on regulating the microstructure and crystallization,inhibiting Sn2+ oxidation and reducing trap states, resultingin an optimal efficiency of 10.33%. This is substantially better thanthat of the reference device (6.42%). Benefiting from the fact thatPI containing -NH- and -NH2 (+)- groups can passivate both positively charged defects andnegatively charged halogen defects, unencapsulated TPSCs modifiedwith the PI material can maintain about 90% of their original efficiencyafter being kept in a N-2 atmosphere for 1000 h, much higherthan the value of 47% in reference TPSCs without additives. This workprovides a practical method to prepare efficient and stable pure TPSCs.