for maximizing power output from an illuminated area is through the use of multijunction solar cell constructs. [3] Recently, we put forward the first sequential series multijunction dye-sensitized solar cell (SSM-DSC), which could power solarto-fuel conversion directly from a single illuminated area. [4] This construct showed solar-to-fuel conversion efficiencies of up to 3% for CO 2 to CO and H 2 O to H 2 and O 2 reactions in the seminal report of a purely DSC-based technology powering these processes from a single illuminated area device without bias. [4b] The use of a DSC system to power these solar-to-fuel conversion processes is attractive due to the processability, stability, and already relatively high photovoltage outputs from DSC devices. [4a] The SSM-DSC construct capitalizes on the high photovoltages of traditional DSC devices in dividing photons according to potential energy to generate high voltage outputs through a summation of subcell photovoltages. SSM-DSC devices are simple to construct with a direct stacking of subcells sequentially wired in series. In this configuration, devices can be optimized individually in terms of TiO 2 thickness and sensitizer choice to achieve well-matched photocurrents for higher performing SSM-DSC devices since current is limited by the lowest current device in the series. However, within this design, significant light losses exist between each subcell, especially at the glass-air interface where diffraction and reflection are the highest due to significantly mismatched refractive indexes of glass (n = 1.52) and air (n = 1) (Figure 1). To minimize these losses, we put forward the use of a simple-to-apply antireflective coating in the form of CYTOP along with an immersion oil with a similar refractive index to glass between each subcell (Figure 2).CYTOP is known in the field of optoelectronics with recent uses as a gate dielectric, a support layer within devices, as a selfcleaning surface, a solution substrate patterning material, and as an insulating tunneling layer within devices. [5] No reports were apparent from our searches for the specific use of CYTOP as an antireflective coating with organic or dye-sensitized solar cells. The use of CYTOP and immersion oil as optical interfacial loss diminishing components allows for an increase of photon flux throughout the SSM-DSC system to boost photocurrent values for a more overall efficient system.
Sequential series multijunction dye-sensitized solar cells (SSM-DSCs) canpower solar-to-fuel processes with a single illuminated area device. Dye selection and strategies limiting photon losses are critical in SSM-DSC devices for higher performance systems. Herein, an efficient and readily applicable spin coating protocol on glass surfaces with an antireflective fluoropolymer (CYTOP) is applied to an SSM-DSC architecture. Combining CYTOP with the use of an immersion oil between glass spacers in a three subcell SSM-DSC with judiciously selected TiO 2 photoanode sensitizers and thicknesses, an overall power conversion efficie...
