Development of high-performance and stable inverted perovskite solar cells via multifunctional interface and bulk defects engineering

Abstract

Energy resources are the foundation and driving force for the progress of human civilization and the improvement of human well-being. However, the extensive use of fossil fuels in industrial activities has caused serious problems, such as energy resource constraints and environmental pollution. Organic-inorganic halide perovskite solar cells (PSCs) show great potential for realizing low-cost and easily fabricated photovoltaics. However, different unintentional defects are formed in polycrystalline perovskite film during the crystal formation process, resulting in poor stability, large hysteresis, and severe non-radiative recombination. Besides, PSCs face the challenge of easy degradation under ambient moisture, temperature, and light, which severely hinders further commercialization. In this thesis, we aim to improve the device efficiency and stability by reducing the defects at the interface and bulk through interface engineering and additive engineering. Firstly, we demonstrate a multifunctional interface layer by establishing perovskite (PVSK) as the ligand of PbS QDs (denoted as PbS-PVSK QDs) to address the challenging issues of unexpected defects and device stability. The novelties of the interface layer are a) in-situ ligand exchange on the perovskite film surface forming strong interaction between perovskites and PbS QDs, b) reduced defects and improved charge extraction, and c) improved device performances and stability by inhibition of iodide ions mobilization. As a result, the champion MAPbI3 based inverted device achieves high PCE up to 20.64% with negligible hysteresis and good reproducibility. Under continuous light soaking in ambient conditions, the time for PSCs with PbS-PVSK QDs interface layer retaining 90% of their initial PCE is nearly three times longer than that of control PCSs. Secondly, we demonstrate a multifunctional strategy for high performance and stability perovskite solar cells by incorporating the 2-(dimethylamino) ethyl methacrylate (DMAEMA) into the perovskite film through simple one-step antisolvent additive engineering (AAE) process. The DMAEMA can be self-polymerized in the perovskite film without any other extra initiator after annealing, contributing to the improved crystallinity of the perovskites. The DMAEMA offers interactions with I2¬ so that the trace amount of iodine that exists as defects in the perovskites can be reduced. Furthermore, the film with the DMAEMA based AAE method has a more uniform composition distribution, contributing to improved phase stability. Consequently, a high PCE of 21.52% is achieved for the DMAEMA-incorporated PSCs with retaining 90% efficiency after more than 600 h continues light illumination due to the suppression of iodine formation, the reduction of uncoordinated Pb2+ and minimization of phase segregation. Finally, the 4-(2-Aminoethyl) benzoic acid hydrobromide (ABABr) is introduced as an interlayer between perovskite and bottom hole transport layer NiOx for reducing the interface redox reaction between Ni3+ and I-, contributing to effectively reduced series resistance and improved device stability. Besides, the interface layer also helps improve the perovskite crystallization and reduce defects density. Therefore, both triple cations and MA free perovskite compositions devices have an improved PCE. More importantly, the stability of perovskite films and PSCs devices are largely improved due to suppressed interface reactions.