Tailoring the buried interface with self-assembled 2-chloroethylphosphonic acid for defect reduction and improved performance of tin-based perovskite solar cells

Abstract

Tin-based perovskite solar cells (Sn-PSCs) have attracted considerable attention for their potential to achieve high efficiency and low toxicity. However, the high density of defect states due to the uncontrolled crystallization and the easy oxidation of Sn²⁺ to Sn⁴⁺ limit the device performance of Sn-PSCs. Herein, a novel halogen-terminated self-assembling molecule, 2-chloroethylphosphonic acid (CEPA), is used to modify the buried interface of Sn-PSCs with polyethylenedioxythiophene:poly(styrene sulfonate) (PEDOT:PSS) as the hole transport layer. The chemical anchoring of CEPA on PEDOT:PSS reduces the excess PSS and contributes to a high-quality tin perovskite film with reduced voids and impurity phases at the buried interface. The reduction of defects for tin perovskites prepared on the CEPA-modified PEDOT:PSS greatly reduces the Urbach energy and inhibits non-radiative energy loss. As a result, the CEPA-modified Sn-PSCs based on FA_0.75MA_0.25SnI₃ perovskite exhibit a PCE of 10.65%, which is nearly 24% higher than that of their pristine counterpart (8.57%). Moreover, the device stability is significantly improved due to the inhibited degradation at the tin-based perovskite/PEDOT:PSS interface. This work demonstrates that buried interface modification using halogen-terminated aliphatic self-assembled molecules is an effective strategy to improve the performance of tin-based perovskite devices.