Dye mixture promoted light harvesting for organic dye-sensitized solar cells using triphenylamine dyes with various numbers of anchoring groups

Co-sensitizers and co-adsorbents are promising materials to enhance the light harvesting efficiency and reduce the un-expected back transfer reaction (recombination) of dye-sensitized solar cells (DSSCs). In this study, three sensitizers with triphenylamine as an electron donor, thiophene as a bridge and various numbers of acceptors/anchors cyanoacetic acid (TPA3T1A, TPA3T2A and TPA3T3A) were synthesized, and TPA3T1A and TPA3T2A were used as co-adsorbents with TPA3T3A. The results showed that co-adsorption on the TiO₂ surface at the following percentages, TPA3T3A 73%, TPA3T1A 17% and TPA3T2A 10%, resulted in an increase in the photovoltaic performance of the DSSCs from 5.27% to 5.83% compared to that of a single TPA3T3A sensitizer due to the increasing J_SC and V_OC. This enhancement might be due to improved light absorption and decreasing recombination by the co-sensitizers, TPA3T1A and TPA3T2A, occupying all the empty plases on the TPA3T3A-adsorbed TiO₂ surface.     

Influence of oligothiophene-functionalized co-sensitizer on the electron injection efficiency for multiple dye-TiO2 interface

Co-sensitizer has been employed in dye-sensitized solar cells (DSSCs) to enhance light harvesting at organic/inorganic heterogeneous. Here, the multiple dyes@TiO₂ interface has been investigated by density functional theory simulations, to explore the role of varied oligothiophene-functionalized co-sensitizers on the electron injection efficiency. In presence of co-sensitizers, the simulated absorption spectra broaden with the increasing of the number of thiophene from 0, 1, to 2. Meanwhile, the co-sensitizer modifies the energy alignment of interface, and influences the electronic coupling between dye and TiO₂. Critically, the ratio of electron-hole recombination and electron injection rates k_rec/k_inj based on Marcus theory for both dye and co-sensitizer decrease significantly with increasing of the number of oligothiophene, resulting in the improved electron injection efficiency. Our result implies that the electron injection efficiency depends on the number of thiophene in co-sensitizer largely, and appropriate number plays an active role in tuning the electronic properties of hybrid heterostructure.     

Low temperature fabrication of hybrid solar cells using co-sensitizer of perovskite and lead sulfide nanoparticles

Our cost-effective approach for hybridizing methylammonium lead iodide and PbS nanoparticles at low temperature (≤100 °C) for photovoltaic devices is introduced. As employed into a perovskite based solar cell platform, effects of PbS on the device performance were investigated. Through experimental observations under simulated air-mass 1.5G illumination (irradiation intensity of 100 mWcm⁻²), the efficiency of a perovskite:PbS device is 11% higher than that of a pristine perovskite solar cell under the same fabrication conditions as a result of the broadened absorption range in the infrared region. The highest photovoltaic performance was observed at a PbS concentration of 2% with an open-circuit voltage, short-circuit current density, fill factor, and power-conversion efficiency of 0.557 V, 22.841 mA cm⁻², 0.55, and 6.99%, respectively. Furthermore, PbS NPs could induce hydrophobic modification of the perovskite surface, leading to an improvement of the device stability in the air. Finally, the low-temperature and cost-effective fabrication process of the hybrid solar cells is a good premise for developing flexible/stretchable cells as well as future optoelectronic devices.     

Two-step annealed CdS/CdSe co-sensitizers for quantum dot-sensitized solar cells

CdS/CdSe co-sensitizers on TiO₂ films were annealed using a two-step procedure; high temperature (300 °C) annealing of TiO₂/CdS quantum dots (QDs), followed by low temperature (150 °C) annealing after the deposition of CdSe QDs on the TiO₂/CdS. For comparison, two types of films were prepared; CdS/CdSe-assembled TiO₂ films conventionally annealed at a single temperature (150 or 300 °C) and non-annealed films. The 300 °C-annealed TiO₂/CdS/CdSe showed severe coalescence of CdSe QDs, leading to the blocked pores and hindered ion transport. The QD-sensitized solar cell (QD-SSC) with the 150 °C-annealed TiO₂/CdS/CdSe exhibited better overall energy conversion efficiency than that with the non-annealed TiO₂/CdS/CdSe because the CdSe QDs annealed at a suitable temperature (150 °C) provided better light absorption over long wavelengths without the hindered ion transport. The QD-SSC using the two-step annealed TiO₂/CdS/CdSe increased the cell efficiency further, compared to the QD-SSC with the 150 °C-annealed TiO₂/CdS/CdSe. This is because the 300 °C-annealed, highly crystalline CdS in the two-step annealed TiO₂/CdS/CdSe improved electron transport through CdS, leading to a significantly hindered recombination rate.