Enhanced light harvesting and charge recombination control with TiO 2 /PbCdS/CdS based quantum dot-sensitized solar cells

Nanocrystals as performance-boosting materials for solar cells

Nanocrystals (NCs) have been widely studied owing to their distinctive properties and promising application in new-generation photoelectric devices. In photovoltaic devices, semiconductor NCs can act as efficient light harvesters for high-performance solar cells. Besides light absorption, NCs have shown great significance as functional layers for charge (hole and electron) transport and interface modification to improve the power conversion efficiency and stability of solar cells. NC-based functional layers can boost hole/electron transport ability, adjust energy level alignment between a light absorbing layer and charge transport layer, broaden the absorption range of an active layer, enhance intrinsic stability, and reduce fabrication cost. In this review, recent advances in NCs as a hole transport layer, electron transport layer, and interfacial layer are discussed. Additionally, NC additives to improve the performance of solar cells are demonstrated. Finally, a summary and future prospects of NC-based functional materials in solar cells are presented, addressing their limitations and suggesting potential solutions.

Improved light-harvesting and suppressed charge recombination by introduction of a nanograss-like SnO2 interlayer for efficient CdS quantum dot sensitized solar cells

Quantum dot sensitized solar cell (QDSSC) performance is primarily limited by the recombination of charges at the interfaces of TiO2/quantum dot (QD) sensitizer/electrolyte. Hence, blocking or suppressing the charge recombination is an essential requirement to elevate the QDSSC performance to the next level. To retard the charge recombination, herein, we propose the introduction of a SnO2 nanograss (NG) interlayer on the surface of TiO2 using the facile chemical bath deposition method. The SnO2 NG interlayer not only inhibits the interfacial recombination processes in QDSSCs but also enhances the light-harvesting capability in generating more excitons. Hence, the TiO2/SnO2 NG/CdS QDSSCs can achieve the power conversion efficiency of 3.15%, which is superior to that of a TiO2/CdS device (2.16%). Electrochemical impedance spectroscopy, open-circuit voltage decay and dark current analyses confirm that the recombination of charges at the photoanode/electrolyte interface is suppressed and the life time is improved by introducing the SnO2 NG interlayer between the TiO2 and CdS QD sensitizer.

ZnSxSe1-x Alloy Passivation Layer for High-Efficiency Quantum-Dot-Sensitized Solar Cells

Interface modification is an important means for improving the performance of almost all optoelectronic devices. In quantum-dot-sensitized solar cells (QDSCs), effective surface modification of photoanode also has a critical impact on photovoltaic performance. At present, ZnS and ZnSe wide band gap semiconductors are the mainstream materials used for photoanode/electrolyte interface passivation in QDSCs. However, the problem with these two materials is that the passivation effect and the lattice match with TiO₂/QD are difficult to be balanced. Although ZnS can form a larger energetic barrier due to the higher conduction band edge, its lattice mismatch with TiO₂ and QD (such as CdSe and CuInSe₂) is large, leading to the formation of additional defect states. On the contrary, ZnSe has a small lattice mismatch with TiO₂ and QD but a relatively lower conduction band edge. Herein, we propose a strategy to employ ZnS_xSe_1-x alloy materials as a passivation layer for the first time to solve the drawbacks of single-component passivation layers. The ZnS_xSe_1-x alloy passivation layer was deposited on the Zn-Cu-In-Se (ZCISe) QD-sensitized TiO₂ film electrode via successive ionic layer adsorption and reaction (SILAR) method. A stable polyselenosulfide/sulfide mixed anions were served as anion precursor for the formation of ZnS_xSe_1-x alloy passivation layer. Experimental results revealed that the alloy passivation layer is more favorable for the suppression of charge recombination at the photoanode/electrolyte interface. In addition, the ZnS_xSe_1-x alloy passivation layer can significantly improve the photogenerated electron extraction efficiency compared to the current classical ZnS passivation layer as confirmed by the transient absorption (TA) measurement. Consequently, the average efficiency of QDSCs was improved from 12.17 to 13.08% with the replacement of traditional ZnS passivation layer by ZnSSe-10 under AM 1.5G one full sun illumination.

Combined photoanodes of TiO2 nanoparticles and {001}-faceted TiO2 nanosheets for quantum dot-sensitized solar cells

A key point for constructing quantum dot-sensitized solar cells (QDSSCs) with high efficiency is to improve the utilization of sunlight.

High current density cation-exchanged SnO2–CdSe/ZnSe and SnO2–CdSe/SnSe quantum-dot photoelectrochemical cells

The 9.74 mA cm⁻² current density of SnO₂–CdSe photoanode is enhanced to 19.82 and 28.40 mA cm⁻² on SnO₂–CdSe/ZnSe and SnO₂–CdSe/SnSe surface modifications, respectively, through a process of cation-exchange.