Highly Efficient Perovskite-CIS Monolithic Tandem Solar Cells

Single-junction perovskite solar cells (PSC) have demonstrated an impressive progress over the last decade, already surpassing 25% of power conversion efficiency (PCE) and quickly approaching their Shockley-Queisser limit.[1,2] In addition, their outstanding properties also make perovskites appealing for implementation on tandem configurations; having achieved a record PCE of 29.5% for a monolithic tandem solar cell (TSC) with a silicon bottom sub-cell.[1] However, silicon-based devices prove inappropriate when flexibility and/or lightweight are required. In this regard, thin film PV technologies, such as CI(G)S-based devices show suitable characteristics and versatility for these kind of implementations.[3]<br/>In this context, we present recent results on highly efficient monolithic perovskite-CIS TSCs. We demonstrate that by optimizing the semi-transparent perovskite top sub-cell when interconnected in tandem with a low band-gap CIS bottom sub-cell, we obtain 2-terminal tandem PV devices exceeding 22% in PCE. We report on the improvements in light management, addressing transparent conductive oxides and anti-reflective coatings along with band-gap tuning to achieve current matching between sub-cells. We also discuss on the benefits of using a CIS absorber with a low band-gap of ca. 1.03 eV for the bottom sub-cell, which allows us to take advantage of the excellent opto-electronic properties of perovskites with band-gaps below 1.60 eV as revealed by advanced characterization techniques. Our study shows that perovskite-CIS TSCs have the potential to reach PCEs above our current results, paving the way for future developments that might push the efficiencies over the 30% threshold.<br/><br/><i>References:</i><br/>[1] NREL. Best Research-Cell Efficiency Chart. Photovoltaic Research 2021 [cited Oct. 2021]. Available from: https://www.nrel.gov/pv/cell-efficiency.html<br/>[2] Min, Hanul, et al. "Perovskite solar cells with atomically coherent interlayers on SnO2 electrodes”. <i>Nature</i> 598.7881 (2021): 444-450.<br/>[3] Jošt, Marko, et al. "Monolithic perovskite tandem solar cells: A review of the present status and advanced characterization methods toward 30% efficiency." <i>Advanced Energy Materials</i> 10.26 (2020): 1904102.