Future Research Directions in Perovskite Solar Cells: Exquisite Photon Management and Thermodynamic Phase Stability

As power conversion efficiency (PCE) of perovskite solar cells (PSCs) has rapidly increased up to 25.7% in 2022, a curiosity about the achievable limit of the PCE has prevailed and demands understanding about the underlying fundamentals to step forward. Meanwhile, outstanding long-term stability of PSCs over 1000 h has been reported at operating conditions or under damp heat test with 85 °C/85% relative humidity. Herein comes the question as to whether the phase stability issue of perovskite crystal is completely resolved in the most recent state-of-the-art perovskite film or if it deceives everyone into believing so by significantly slowing the kinetics. On the one hand, the fundamental origins of a discrepancy between reported values and the theoretical limit are thoroughly examined, where the importance of light management is greatly emphasized with the introduction of external luminescence as a key parameter to narrow the gap. On the other hand, the phase stability of a perovskite film is understood from thermodynamic point of view to address viable approaches to lower the Gibbs free energy, distinguishing the kinetically trapped condition from the thermodynamically stable phase.