Lately, scientists have been exploring diverse solar cell configurations to enable their widespread use. Organic solar cells utilizing perovskite materials offer numerous benefits compared to traditional silicon-based designs, such as reduced fabrication expenses, increased flexibility, and customizable properties.
Efficiency More Than That of Silicon Solar Cells
Organic solar cells have achieved a top-certified power conversion efficiency (PCE) of 19.4%, less than silicon solar cells. A proposed approach to enhance their efficiency and durability involves integrating them with mixed halide wide-bandgap perovskite cells, forming perovskite/organic tandem solar cells.
Although perovskite/organic tandem solar cells hold promise for achieving high PCEs and stabilities, their performance is impeded by a phenomenon called phase segregation. This process deteriorates the performance of wide-bandgap perovskite cells and subsequently impacts recombination processes at the interface layer of the tandem solar cells.
Scientists from the Suzhou Key Laboratory of Novel Semiconductor-optoelectronic Materials and Devices at Soochow University have developed a method to mitigate phase segregation in wide-bandgap perovskites, enhancing the efficiency and stability of perovskite/organic tandem cells. As described in a publication in Nature Energy, this approach involves integrating a pseudo-triple-halide alloy into mixed halide perovskites composed of iodine and bromine.
Iodide/Bromide Mixed Halide Perovskites
In their study, Zhichao Zhang, Weijie Chen, and their team noted that mixed halide wide-bandgap perovskites are well-suited for inclusion in tandem photovoltaic setups like perovskite/organic tandem solar cells.
However, they pointed out that halide phase segregation, stemming from halogen vacancy-induced ion migration in wide-bandgap perovskites, constrained device efficiency and longevity. To address this, they introduced pseudo-halogen thiocyanate (SCN) ions into iodide/bromide mixed halide perovskites, demonstrating improved crystallization and reduced grain boundaries.
The scientists observed that incorporating their pseudo-halogen thiocyanate ions into iodine/bromide mixed halide perovskites prevented the separation of halide components within the solar cells. Thiocyanate slowed down crystallisation, preventing ion migration and thereby facilitating the flow of electric charge within the solar cell.
“Even small quantities of SCN ions within the perovskite lattice form an I/Br/SCN alloy, filling iodine vacancies and impeding halide ion migration through steric hindrance," explained Zhang, Chen, and their team. "These combined effects inhibit halide phase segregation during operation, leading to decreased energy loss in the wide-bandgap perovskite cells.”
25.82% Initial Power Conversion Efficiency Achieved
To evaluate the effectiveness of their proposed approach in mitigating phase segregation in wide-bandgap perovskites, the researchers implemented it in the fabrication of perovskite/organic tandem solar cells. Initial tests revealed that these tandem solar cells achieved a power conversion efficiency (PCE) of 25.82%, a certified PCE of 25.06%, and demonstrated operational stability for 1,000 hours.
Looking ahead, the methodology outlined by Zhang, Chen, and their team could be modified and extended to other wide-bandgap perovskites with diverse compositions. This advancement holds potential for developing innovative perovskite/organic photovoltaic systems that exhibit stability across varying light conditions, boast high PCEs, and maintain operational integrity for extended durations.