Efficient perovskite/silicon tandem with asymmetric self-assembly molecule

Achieving highly ordered and uniformly covered self-assembled monolayers with optimal packing configuration on textured silicon substrates remains a critical challenge for further improving the efficiency of perovskite/silicon tandem solar cells^1-3. Here we design an asymmetric self-assembled monolayer (named as HTL201) featuring an anchoring group and a spacer flanking a carbazole core, serving as a hole-selective layer for perovskite/silicon tandem solar cells. When compared with symmetric self-assembled monolayers with a nitrogen-bonded phosphonic acid group, the HTL201 molecule shows minimized steric hindrance and improved coverage on the transparent conductive oxide recombination layer. The strong coordination interaction between HTL201 and the perovskite film effectively reduces non-radiative recombination at the buried interface. Notably, the optimized energy-level alignment between the perovskite and HTL201, accompanied by an increase in the quasi-Fermi-level splitting value of the perovskite layer, enables an impressive voltage of nearly 2 V for perovskite/silicon tandem solar cells, resulting in a certified power conversion efficiency of up to 34.58% based on a silicon heterojunction solar cell.