Enhanced performance of PbS-sensitized solar cells via controlled successive ionic-layer adsorption and reaction

Abstract

Despite the potential of PbS quantum dots (QDs) as sensitizers for quantum-dot-sensitized solar cells (QDSSCs), achieving a high photocurrent density over 30 mA cm(-2) remains a challenging task in PbS-sensitized solar cells. In contrast to previous attempts, where Hg(2+)-doping or multi-step post-treatment is necessary, we are capable of achieving a high photocurrent exceeding 30 mA cm(-2) simply by manipulating the successive ionic layer adsorption and reaction (SILAR) method. We show that controlling temperature at which SILAR is performed is critical to obtain a higher and more uniform coverage of PbS QDs over a mesoporous TiO2 film. The deposition of a CdS inter-layer between TiO2 and PbS is found to be an effective means of ensuring high photocurrent and stability. Not only does this modification improve the light absorption capability of the photoanode, but it also has a significant effect on charge recombination and electron injection efficiency at the PbS/TiO2 interface according to our in-depth study using electrochemical impedance spectroscopy (EIS). The implication of subtle changes in the interfacial events via modified SILAR conditions for PbS-sensitized solar cells is discussed.

Strategic PbS quantum dot-based multilayered photoanodes for high efficiency quantum dot-sensitized solar cells

“…Furthermore, CdS/PbS/In2S3 multilayered photoanode with an optimum CdS deposition prior to PbS [19], confirmed an improved PCE value of 4.3% (36% more than that of PbS standard QDSSC), which is credited to the increase in JSC from 21.6 to 25.7 mA/cm 2 by enhanced loading of PbS QDs as proven in Fig. 1d in addition to the increase in VOC by In2S3 layer.…”

“…It should be noted that the light absorbance of CdS is higher than that of In2S3 due to its smaller band gap, which is the reason for the large scontribution of CdS interlayer to JSC than In2S3 layer [42,45,46]. Therefore, CdS (Eg ≈ 2.4 eV) or other similar interfacial layer deposited on mesoporous TiO2 prior to the main absorber QDs with a smaller Eg is an effective strategy to improve the photocurrent density by absorbing high-energy photons and enhancing QDs loading [19,42,46,51,52]. However, the VOC value was rarely affected by the CdS interlayer because, as shown in Fig.3c, it hardly restricted the electron back-transfer and recombination via the route 2 due to its position, which is a main recombination route for the carriers generated from PbS.…”

“…Recently a JSC of more than 30 mA/cm 2 has been reported by properly tuning the deposition conditions of PbS through successive ionic layer adsorption and reaction (SILAR) [19,20]. While the narrow band gap of PbS gives it an advantage to attain a high JSC, it also has a detrimental effect of reducing the open-circuit voltage (VOC).…”

“…PbS is potent material with a narrow band gap which can achieve a high photocurrent (JSC) [14,19,20,26,[41][42][43]. Recently a JSC of more than 30 mA/cm 2 has been reported by properly tuning the deposition conditions of PbS through successive ionic layer adsorption and reaction (SILAR) [19,20].…”

“…However, the QDSSCs still keep showing the vast potential for further enhancements [11][12][13]. Quantum dots (QDs) offer various advantages over organic and metal complex dyes as sensitizer such as ability to tune bandgap by varying the size [14][15][16][17][18], simple processability [19][20][21][22][23], high extinction coefficient [24,25] and possibility to generate multiple excitons from single photon. [26][27][28][29] While the search for active electrocatalysts as the counter electrode in polysulfide environment had led the way to improve the performance of QDSSCs in the past years, focus has been shifted again to develop more suitable photoanodes in the recent years [30][31][32][33][34].…”