Reflective perovskite solar cells for efficient tandem applications

Tandem solar cells combining a wide bandgap, efficient perovskite absorber with a low bandgap photovoltaic module, such as a c-Si cell, can potentially achieve a high theoretical efficiency of over 30%. Instead of using the conventional parallel stacking tandem, we report here a reflective tandem configuration, with the perovskite solar cell acting as the spectral filter that absorbs high energy photons, while sub-bandgap photons are reflected to a Si sub-cell using a highly reflective back metal electrode. The perovskite solar cell exhibits a high reflectance of over 60% in the near infrared spectral region, which allows the subsequent silicon cell to absorb photons in this region, resulting in a high current density of 13.03 mA cm^-2. In such a tandem configuration, we achieved a combined efficiency of 23.1% using a four-terminal measurement. This result demonstrates the promise of employing perovskite solar cells in a reflective tandem for a high efficiency solar energy conversion system, with an efficiency of up to 30%.