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Luminescent nanophosphors as spectral converters offer immense potential for dye‐sensitized photovoltaics (DSPV) to harvest a wide range of the solar spectrum. Herein, a novel structural design of DSPV using a downconversion (dc) nanophosphor layer in the TiO2 photoanode for both indoor (ambient) and outdoor applications is demonstrated. Cubic SrF2:Pr3+−Yb3+ nanoparticles are synthesized by a template‐free hydrothermal technique. The dc nanophosphor absorbs photons of the blue region, leading to emission of a broad luminescence band (green and red), which is well matched with N719‐dye absorption. The mixed‐valence state of Pr ions (Pr3+ and Pr4+) leads to trap‐assisted transition levels, which result in a broad visible emission. For the first time, a unique Pr3+−Yb3+ codoped dc system yielding tuned and intensified luminescence by effective crossrelaxation (CR) with a back energy transfer (BET) mechanism is designed and efficient working of the dc nanophosphor‐layered DSPVs under both outdoor 1 sun (AM 1.5 G) and indoor light (Warm‐3200 K; Day‐5000 K) conditions is demonstrated. Improved efficiency of 9.07% is attained in dc‐dye‐sensitized solar cells (DSSC) compared with a control‐DSSC (8.39%) at 1 sun intensity. Under indoor low‐light conditions (1000 lux), the dc‐DSPV achieves high power conversion efficiencies (PCEs) of 14.85 and 15.9%, respectively. This approach results in a 63.44% increment in output power density for dc‐DSPV compared with the control‐DSPV under LED 3200 K irradiation. These findings suggest that this configuration of dc‐layered DSPV can provide a new strategy for future indoor electronic operations under ambient light conditions.

Conventional dye-sensitized solar cells (DSSCs) involving charge-transfer interfaces face charge injection losses and offsets for TiO 2 -sensitizer band alignment. The direct chargetransfer mechanism in DSSCs with catechol (CT, 1,2-benzenediol)-based compounds minimizes the injection losses and eliminates band alignment issues, although the photovoltaic performance of the corresponding device is very poor due to the ultrafast (picosecond) recombination of photoexcited electrons. Just as in a natural photosystem, structural selectivity toward inhibition of this recombination needs to be defined. The interfacial electron density and back electron transfer kinetics at the molecular sensitizer−TiO 2 interface play a significant role in the overall energy conversion efficiency. Herein, we identified, for the first time, that the π-electron cloud at the sensitizer−TiO 2 interface facilitates the degree of recombination. Comparative density functional theory analyses confirmed that these electron clouds act as large recombination sites. Luminol (LM) and isoluminol (ILM) were employed as "small molecule" sensitizers without the cloud, having a secondary amine linker, which increased the photoenergy conversion efficiency of the single-step sensitization-based photovoltaic cell (type-II DSSC) by reducing the recombination. The device with LM exhibited a power-conversion efficiency (PCE) of ca. 1.11% (representing 363% improvement when compared to CT), the highest ever reported in this category. This understanding is insightful for the design of novel small molecular sensitizers for future DSSCs.

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The steric shielding offered by sensitizers on semiconducting surfaces as a result of branching in the dyes used offers the less utilization of semiconducting substrate sites during device fabrication in dye-sensitized solar cells (DSSCs). This work proposes a strategy to increase the coverage through the utilization of small molecules which have the ability to penetrate into the sites. The small molecules play the dual role of vacancy filling and sensitization, which can be viewed as an alternative to co-sensitization also. Hence, we show for the first time ever that the co-adsorption of catechol with Z907 as a sensitizer enhances the electron density in the photo-anode by adsorbing on the vacant sites. Catechol was subsequently adsorbed on TiO2 after Z907 as it has a stronger interaction with TiO2 owing to its favorable thermodynamics. The reduced number of vacant sites, suppressed charge recombination, and enhanced spectral response are responsible for the improvement in the PCEs. Quantitatively, both organic and aqueous electrolytes were used and the co-sensitized DSSCs had PCE enhancements of 7.2 and 60%, respectively, compared to the control devices.