Tandem solar cells (TSC) operate on the principle of separating incident sunlight into different energy streams, with each sub-cell tailored to harvest a specific portion of the solar spectrum. The top cell functions as a high-energy filter, primarily absorbing short-wavelength photons, while the bottom cell serves as a low-bandgap absorber, capturing relatively longer-wavelength light that transmits through the upper layer. Among emerging photovoltaic materials, PbS QD can be viewed as tunable absorbers, with the bandgap precisely adjustable by controlling particle size. This unique feature makes them highly attractive for low-cost, solution-processable solar technologies. However, device performance is often limited by interfacial defect states, which act as recombination centers and disrupt charge extraction.
To address this challenge, researchers led by Professors Haisheng Song and Jiang Tang at Huazhong University of Science and Technology (HUST), China, introduced an ultrathin chlorinated conjugated polymer (D18-Cl) as an interfacial modification layer. This strategy can be visualized as inserting a nanoscale protective and adaptive interlayer between delicate stacked components, similar to placing a shock-absorbing film between fragile glass sheets during fabrication. The polymer not only protects the surface of QDs during subsequent processing steps but also chemically passivates defects by coordinating with undercoordinated lead atoms and healing sulfur vacancies, effectively eliminating microscopic recombination pathways. Furthermore, this interlayer optimizes the interfacial energy landscape, enabling charge carriers to transport more efficiently. As a result, non-radiative recombination is significantly suppressed, and charge extraction is substantially improved. This interface-engineering strategy led to a record power-conversion efficiency of 10.36% for semi-transparent WBG top cell and 13.148% for all-PbS QD TSC, along with a fill factor exceeding 73%. The devices also exhibited excellent operational stability during operation testing. The work, titled “Chlorinated conjugated copolymer interface modification enables record-efficiency of all-PbS quantum dot tandem solar cells”, was published in Frontiers of Optoelectronics (published on May 22, 2026).
DOI: 10.2738/foe.2026.0024