Dimension-Controlled SnO₂ Nanostructures for High Performance Flexible Perovskite Solar Small-Modules (900cm²)

In the past decade, organic-inorganic hybrid metal halide perovskites have attracted much attention as potential photovoltaic (PV) materials owing to their attractive advantages such as high absorption coefficients, tunable bandgaps, long carrier diffusion length, low cost, flexibility, and low processing temperature. In particular, owing to low crystallization temperature (&lt;150 ^oC), perovskites can be applied to a polymer substrate. This would make it possible to develop flexible perovskite solar cells (PSCs) that could open the door to low-cost mass production through roll-to-roll processes in the near future. In addition, the development of flexible PSCs has shown great potential in the field of wearable power supplies and integration with architectures in the future. However, despite the rapid development of low-temperature-processed PSCs, the power conversion efficiencies of flexible PSCs using polymer substrates are still inferior owing to the limitation of the electron transport layer (ETL) using colloidal nanoparticles (NP). Furthermore, ensuring both the efficiency and stability of flexible PSCs remains a considerable challenge for their commercialization.<br/>In this study, we found for the first time that these solar cells suffer from a trade-off relationship between efficiency and stability due to the off-balance between surface coverage and the charge-transporting property of electrodes fabricated from a conventionally used colloidal Tin(IV) oxide (SnO₂) nanoparticles (NP). To resolve this trade-off, we designed a new electrode by controlling the dimensionality of the NPs. The development of multidimensional (MD) electrodes enables a PCE of 22.0% (0.094 cm²) on a flexible substrate. When applied to the large area module, flexible modules show a PCE loss of nearly 10% by module size from mini-module to small-module (Type of Module is divided into mini-module (&lt; 200cm²), sub-module (200-800cm²) and small-module (800-6500 cm²) depending on the size of modules). Moreover, when the MD electrode is applied to the flexible sub-module (400cm²) and small-module (900cm²), the PCEs of MD electrode f-PSMs are 17.3% (active areas: 364cm²) and 17.7% (active areas: 837cm²). These results are the highest PCE reported to date. Furthermore, PSCs and the f-PSM based on the MD electrode retain 86% and 80% after 500h and 300h under continuous operation conditions, respectively. We believe that our strategy provides a new way to realize highly efficient and stable flexible perovskite photovoltaics.