Large Area 23%-Efficient Monolithic Perovskite/Homo-Junction-Silicon Tandem Solar Cell with Enhanced UV Stability Using Down-Shifting Material

Abstract

UV induced degradation is a big issue for perovskite-based solar cells. Parasitic ultraviolet (UV) absorption by the “sun-facing” carrier transport layer in a perovskite cell also hinders the electrical performance when the cell is a top cell for a Si-based tandem. In this work, we tackle these issues by applying textured polydimethylsiloxane (PDMS) films that incorporate a down-shifting material (Ba,Sr)2SiO4:Eu2+ micron phosphor on the front of monolithic perovskite/silicon tandem cells. This film serves multiple purposes optically: antireflective control for the top cell, light trapping in the Si cell as well as absorbing UV and re-emitting green light with high quantum yield. The morphology of the phosphor, optical properties of the phosphor as well as the phosphor incorporated film, water, moisture, UV stability as well as the mechanical flexibility of the anti-reflective down-shifting film were investigated. The effect of phosphor concentration in the antireflective PDMS film on tandem device efficiencies was also studied. This down-shifting antireflective film is suitable for large areas. When applied onto a 4 cm2 monolithic perovskite/silicon tandem solar cell, the power conversion efficiency was improved from 20.1% (baseline device without any anti-reflective film) to 22.3% (device with anti-reflective film but without the phosphors) and to 23.1% (device with down-shifting and antireflective film). The steady-state efficiency of 23.0% and a high FF of 81% achieved by the champion device are the highest values to date for a monolithic perovskite/Si tandem that uses homo-junction-silicon bottom cell. Moreover, results of continuous UV irradiation test show that this composite down-shifting antireflection film significantly enhances the UV stability for the tandem device. The demonstrated efficiency and stability enhancement achieved by such elegant approach paves a way for improving the commercial viability of perovskite/silicon tandems and other perovskite photovoltaic applications.