Boosting the Efficiency of Quantum Dot-Sensitized Solar Cells through Formation of the Cation-Exchanged Hole Transporting Layer

Abstract

In search of a viable way to enhance the power conversion efficiency (PCE) of quantum dot-sensitized solar cells, we have designed a method by introducing a hole transporting layer (HTL) of p-type CuS through partial cation exchange process in a postsynthetic ligand-assisted assembly of nanocrystals (NCs). High-quality CdSe and CdSSe gradient alloy NCs were synthesized through colloidal method, and the charge carrier dynamics was monitored through ultrafast transient absorption measurements. A notable increase in the short-circuit current concomitant with the increase in open-circuit voltage and the fill factor led to 45% increment in PCE for CdSe-based solar cells upon formation of the CuS HTL. Electrochemical impedance spectroscopy further revealed that the CuS layer formation increases recombination resistance at the TiO/NC/electrolyte interface, implying that interfacial recombination gets drastically reduced because of smooth hole transfer to the redox electrolyte. Utilizing the same approach for CdSSe alloy NCs, the highest PCE (4.03%) was obtained upon CuS layer formation compared to 3.26% PCE for the untreated one and 3.61% PCE with the conventional ZnS coating. Therefore, such strategies will help to overcome the kinetic barriers of hole transfer to electrolytes, which is one of the major obstacles of high-performance devices.

Improving the Power‐Conversion Efficiency through Alloying in Common Anion CdZnX (X=S, Se) Nanocrystal Sensitized Solar Cells

“…Formation of the alloy structure removes the defect states within the NCs limiting the charge carrier trapping process. [28,31,39] In this work, with the help of ultrafast spectroscopy and photovoltaic measurements on homogeneous alloyed CdZnX NCs we have further shown here that they are better candidates for solar cell application compared to CdX NCs as they do not suffer from interfacial traps. These observations have been summarized in Scheme 1 below.…”

“…[15,31,[36][37][38][39][40][41] Briefly, TiO 2 photoanodes with transparent layer were prepared through doctor blade technique followed by annealing at 450°C for 30 minutes. [15,31,[36][37][38][39][40][41] Briefly, TiO 2 photoanodes with transparent layer were prepared through doctor blade technique followed by annealing at 450°C for 30 minutes.…”

Correlating Charge‐Carrier Dynamics with Efficiency in Quantum‐Dot Solar Cells: Can Excitonics Lead to Highly Efficient Devices?

“…However, organic hole‐transporting materials are costly and synthetically difficult to prepare, inorganic hole‐transporting materials, on the other hand, are cheap and easy to deposit. We recently demonstrated that CuS is a hole‐transporting layer that can effectively enhance the PCE of QDSSCs in case of post‐synthetic, ligand‐assisted assembly of NCs on TiO 2 . CdSe and two different CdSeS NCs were synthesized and characterized through steady‐state and time‐resolved spectroscopy (Figure ).…”

“…We recently demonstrated that CuS is ah oletransporting layer that can effectively enhance the PCE of QDSSCs in case of post-synthetic,l igand-assisted assembly of NCs on TiO 2 . [39] CdSe and two different CdSeS NCs were synthesized and characterized through steady-state and time-resolved spectroscopy (Figure 9).…”

“…Reproduced with permission from ref. [39];copyright American Chemical Society. alignment as explained earlier.T he NCs were deposited on TiO 2 photoanodes after ligand exchange with mercaptopropionic acid (MPA).…”