ZnS Ultrathin Interfacial Layers for Optimizing Carrier Management in Sb2S3-based Photovoltaics

Monolithic Two-Terminal Tandem Solar Cells Using Sb2S3 and Solution-Processed PbS Quantum Dots Achieving an Open-Circuit Potential beyond 1.1 V

Multijunction solar cells have the prospect of a greater theoretical efficiency limit than single-junction solar cells by minimizing the transmissive and thermalization losses a single absorber material has. In solar cell applications, Sb2S3 is considered an attractive absorber due to its elemental abundance, stability, and high absorption coefficient in the visible range of the solar spectrum, yet with a band gap of 1.7 eV, it is transmissive for near-IR and IR photons. Using it as the top cell (the cell where light is first incident) in a two-terminal tandem architecture in combination with a bottom cell (the cell where light arrives second) of PbS quantum dots (QDs), which have an adjustable band gap suitable for absorbing longer wavelengths, is a promising approach to harvest the solar spectrum more effectively. In this work, these two subcells are monolithically fabricated and connected in series by a poly(3,4-ethylene-dioxythiophene) polystyrene sulfonate (PEDOT:PSS)-ZnO tunnel junction as the recombination layer. We explore the surface morphology of ZnO QD films with different spin-coating conditions, which serve as the PbS QD cell's electron transport material. Furthermore, we examine the differences in photogenerated current upon varying the PbS QD absorber layer thickness and the electrical and optical characteristics of the tandem with respect to the stand-alone reference cells. This tandem architecture demonstrates an extended spectral response into the IR with an open-circuit potential exceeding 1.1 V and a power conversion efficiency of 5.6%, which is greater than that of each single-junction cell.

4.9% Efficient Sb2S3 Solar Cells from Semitransparent Absorbers with Fluorene-Based Thiophene-Terminated Hole Conductors

Fluorene-based hole transport materials (HTMs) with terminating thiophene units are explored, for the first time, for antimony sulfide (Sb₂S₃) solar cells. These HTMs possess largely simplified synthesis processes and high yields compared to the conventional expensive hole conductors making them reasonably economical. The thiophene unit-linked HTMs have been successfully demonstrated in ultrasonic spray-deposited Sb₂S₃ solar cells resulting in efficiencies in the range of 4.7-4.9% with an average visible transmittance (AVT) of 30-33% (400-800 nm) for the cell stack without metal contact, while the cells fabricated using conventional P3HT have yielded an efficiency of 4.7% with an AVT of 26%. The study puts forward cost-effective and transparent HTMs that avoid a post-coating activation at elevated temperatures like P3HT, devoid of parasitic absorption losses in the visible region and are demonstrated to be well aligned for the band edges of Sb₂S₃ thereby ascertaining their suitability for Sb₂S₃ solar cells and are potential candidates for semitransparent applications.

Controllable Solution-Phase Epitaxial Growth of Q1D Sb2 (S,Se)3 /CdS Heterojunction Solar Cell with 9.2% Efficiency

Antimony sulfoselenide (Sb₂ (S,Se)₃ ) is a promising photoabsorber for stable and high efficiency thin film photovoltaics (PV). The unique quasi-1D (Q1D) crystal structure gives Sb₂ (S,Se)₃ intriguing anisotropic optoelectronic properties, which intrinsically require the optimization of crystal growth orientation, especially for electronic devices with vertical charge transport such as solar cells. Although the efficiency of Sb₂ (S,Se)₃ solar cells has been improved greatly through optimizing the material quality, the fundamental issue of crystal orientation control in polycrystalline films remains unsolved, resulting in charge carrier recombination losses in the device. Herein, the epitaxial growth of vertically-oriented Sb₂ (S,Se)₃ film on hexagonal CdS is successfully realized via a solution-based synergistic crystal growth process. The crystallographic orientation relationship between Sb₂ (S,Se)₃ light absorber and the CdS substrate has been rigorously investigated. The best performing Sb₂ (S,Se)₃ solar cell shows a high power conversion efficiency of 9.2% owing to the faster charge transport in the bulk and the efficient charge extraction across the heterojunction. This study points to a new direction to control the crystal growth of mixed-anion Sb₂ (S,Se)₃ , which is crucial to achieve high efficiency solar cells based on antimony chalcogenides with low dimensionality.