Near‐Infrared‐Transparent Perovskite Solar Cells and Perovskite‐Based Tandem Photovoltaics

4][5][6] To make the PV technology more costcompetitive compared to other conventional sources of energy and to further fuel its rapid deployment, the levelized cost of electricity (LCOE) of a PV system needs to be reduced.In a PV system, apart from PV modules, other constituent components such as mounting unit, wiring, inverters, and battery storage constitute about 55% of the total cost. [7,8]These components are generally referred to as the balance of system (BOS).The BOS cost scales proportionally with the area of solar panel installation.An ideal way to reduce the LCOE is by increasing the efficiency of the PV modules. [8]he efficiency of well-established solar cell technologies (Figure 1) such as crystalline silicon (c-Si), gallium arsenide (GaAs) and copper indium gallium selenide (CIGS) are progressing toward the Shockley-Queisser (S-Q) limit, leaving limited room for further improvement in their performance.The thermalization and non-absorption losses incurred in these solar cells mainly restrict their spectral utilization and, consequently, their performance.However, the thermalization losses incurred in single-junction solar cells can be mitigated by combining a wide-bandgap cell with a lowbandgap cell in a multijunction solar cell design, which possesses the ability to achieve efficiencies that surpass the S-Q limit of single-junction solar cells.The practical implementation of multijunction solar cells (MJSCs) utilizing III-V materials have achieved great success in the past. [9]Under 1 sun illumination, LG Electronics and Sharp Corporation have demonstrated monolithic two-terminal MJSC devices using 2-junction (InGaP/GaAs) and 3-junction (InGaP/GaAs/InGaAs) absorber layers to attain power conversion efficiencies (PCEs) of 32.8% [10] and 37.8% [11] respectively.In 2013, Spectrolab utilized a direct bonding technique to grow a lattice-matched 5-junction monolithic MJSC device and demonstrated an efficiency of 38.8% under 1 sun illumination. [12]Very recently, NREL developed a 6-junction monolithic MJSC device to demonstrate a PCE of 39.2% under 1 sun illumination. [13]espite achieving efficiencies beyond the S-Q limit of singlejunction solar cells, the deployment of III-V MJSCs is limited to space applications due to their high manufacturing cost coupled with slow and complicated fabrication procedures. [14]tal halide perovskite solar cells (PSCs) have gained tremendous attention due to their high power conversion efficiencies (PCEs) and potential for low-cost manufacturing.Their wide and tunable bandgap makes perovskites an ideal candidate for tandem solar cells (TSCs) with well-established narrow bandgap photovoltaic technologies, such as crystalline silicon and Cu(In,Ga)Se 2 , to boost the PCEs beyond the Shockley-Queisser limit at affordable additional cost.Although perovskite-based TSCs have shown rapid progress over the past few years, they are far from reaching their practical efficiency limit.In addition, technology commercialization needs to overcome several challenges such as processing upscalability and long-term operational stability of solar modules.In this review, a comprehensive overview of the recent progress of perovskitebased TSCs is provided and the key challenges in the field are discussed.First, the structural and optoelectronic properties of metal halide perovskite materials and preparation methods of metal halide perovskite layers are introduced.Next, the important constituents of near-infrared (NIR) transparent PSCs for achieving high efficiency along with high NIR transmittance are highlighted.Then the developments in perovskite-based TSCs are reviewed, the limiting factors are outlined, and strategies to boost the efficiencies well beyond 30% are provided.Finally, the review is concluded by highlighting the bottlenecks for commercialization and providing an outlook for technology advancement.