Chemical vapor deposition grown formamidinium perovskite solar modules with high steady state power and thermal stability

Metal organic halide perovskites are promising materials for solar cells with a maximum certified efficiency of 22.1%. However, there are only a handful of reports on larger area modules, where efficiencies drop with increasing use of the active area. Chemical vapor deposition (CVD) is a technology used in many industrial applications demonstrating potential for scale up. We used a CVD process to fabricate MAPbI₃ and FAPbI₃ based solar cells with power conversion efficiencies (PCEs) up to 15.6% (MAI, 0.09 cm²) and 5 × 5 cm modules with 9.5% (FAI, 5-cell modules, total active area 8.8 cm²) and 9.0% (FAI, 6-cell modules, total active area 12 cm²). To further investigate scaling issues, we fabricated modules using an established MAPbI₃ solution process, and demonstrated maximum PCEs of 18.3% (MAI, 0.1 cm²), 14.6% (MAI, 1 cm² single cells), and 8.5% at 5 × 5 cm (MAI, 6-cell module, total active area 15.4 cm²). The solution processed cells performed better than CVD cells when comparing PCEs determined from J-V measurements, but the steady state power of solution processed solar cells decreased quickly with increasing area. This decrease in power was correlated with rapid heating of the solar cells under 1 sun illumination, with a pronounced drop in performance at the phase transition temperature of MAPbI₃. In contrast, FAPbI₃ CVD grown solar modules maintained much of their PCEs transitioning from J-V measurements to the steady state operating conditions (1 sun), suggesting that the FAI based CVD process may outperform MAI based solution processed modules when scaled up to practical sizes.