Enhanced performance of inverted perovskite solar cells with buried interface modified by 1-(4-bromophenyl)piperazine layer

In inverted perovskite solar cells (PSCs), the buried interface between the perovskite film and the substrate is crucial for device performance. Although substantial optimization has primarily targeted the top surface of perovskite films, the buried interface remains a key factor, and the buried interface presents greater challenges for investigation due to its non-exposed nature. Moreover, the mismatch in thermal expansion coefficients between the substrate and the perovskite film during the annealing process induces stress accumulation at the interface. This residual stress can cause lattice distortion, leading to an uneven film distribution and reduced crystallinity of the perovskite layer. As a result, dense void defects tend to form at the buried interface, triggering significant non-radiative recombination and substantially degrading the overall performance of the device. In this research, a 1-(4-bromophenyl)piperazine (PDBr₂) buffer layer is incorporated at the buried interface to alleviate the thermal expansion mismatch between the perovskite film and substrate, which helps release residual lattice stress in the perovskite layer. This reduction in stress facilitates the formation of a void-free buried interface and enhances the film's crystallinity, resulting in high-quality perovskite layers. After optimization with PDBr₂, the tensile stress in the perovskite layer decreases from 28.47 MPa to 20.15 MPa, while the void area ratio drops from 2.41 % to 0.43 %. Consequently, the power conversion efficiency (PCE) of inverted PSCs increases to 21.48 %, compared to 18.68 % in the control device, representing a 10.65 % improvement. Additionally, the hysteresis factor is reduced from 0.11 to 0.025. Moreover, the unencapsulated device retains 86.4 % of its initial efficiency after 500 hours in a 60°C nitrogen environment, demonstrating significantly improved overall stability.