A team of researchers from Suzhou University, in collaboration with the Hong Kong Polytechnic University, has created a composite layer that does not contain indium. This material utilizes a molecular bridge between perovskite and silicon to enhance the efficiency and long-term stability of tandem solar cells.
Researchers from Suzhou University, led by Professors Yan Xinbo and Zhang Xiaohun, developed this composite layer in cooperation with the Hong Kong Polytechnic University and various partners from the photovoltaic industry. It forms a molecular bridge between the perovskite and crystalline silicon layers in tandem solar cells. This achievement resolves two serious problems facing perovskite and silicon-based tandem photodetectors: charge loss at the interface of the two materials and reduced long-term stability, which hindered the commercial implementation of such architectures.
The molecular bridge functions at the atomic level. The Suzhou team developed a self-assembling monolayer that chemically bonds to both the perovskite surface and the silicon surface. This creates a continuous electronic pathway for efficient charge transport while passivating defects and suppressing non-radiative recombination.
The elimination of indium is particularly significant. Indium tin oxide has traditionally been used as a transparent conductive layer in displays and photovoltaic devices. However, indium is classified as a critical material subject to concentration risks in the supply chain and rising costs due to demand from the display industry. The new composite layer completely excludes indium, replacing it with more accessible and less expensive materials that provide comparable or better optical transparency and electrical conductivity. This substitution removes both the cost barrier to the commercialization of tandem solar cells and the risk of material supply disruption that concerned the photovoltaic industry.
This research marks progress toward the industrialization of next-generation photovoltaic technologies. Theoretically, perovskite-silicon tandem cells can demonstrate efficiencies exceeding the Shockley-Queisser limit for single-junction silicon cells, which is around 29%. Laboratory tandem cells have already exceeded 33% efficiency, but translating these results into commercially viable products requires solving issues of interface stability and production scalability, which is the focus of the molecular bridge approach. The Suzhou team's work suggests that molecular engineering at the perovskite-silicon interface can simultaneously improve efficiency and operational lifespan, eliminating two of the most critical obstacles to commercialization. The model of university-industry collaboration accelerates the transition from laboratory development to manufacturing. With successful scaling, the molecular bridge technique could strengthen China's leadership in solar energy while reducing dependence on indium.
Scientists from China have developed a three-layer solar cell combining perovskite and silicon, which demonstrated a record voltage of 3.15 volts. The main breakthrough was the successful stabilization of the most vulnerable top perovskite layer using an organic salt.
Tandem (two-layer) solar cells provide higher efficiency compared to standard silicon cells due to more effective utilization of sunlight. However, the design is not limited to two layers; it is possible to add a third, fourth, or even fifth photoactive layer. To achieve maximum overall efficiency, the bandgap of the upper layers must be wider, as photons must be distributed among the layers in decreasing order of energy.
Unlike three-layer cells based on gallium arsenide and III-V semiconductors, which are already used in space with efficiencies exceeding 40 percent, analogues based on perovskites and silicon face difficulties. The bottom layer is usually silicon with a bandgap of 1.12 electron volts, while the second and third layers are perovskite. The greatest challenge lies in obtaining and maintaining the stability of the third layer, which requires a bandgap of 1.8 electron volts or higher.
To widen the perovskite bandgap, some iodine ions in the crystal lattice are replaced by bromine. Excessive bromine content triggers phase segregation: ions begin to migrate, leading to the formation of heterogeneous regions with different compositions—where bromine predominates and where iodine predominates.
Chinese material scientists led by Haijian Tan from Nanjing University managed to create an effective and stable three-layer perovskite cell. The design utilized a textured silicon heterostructure cell as the bottom layer. Above it is a perovskite with a bandgap of 1.52 electron volts, and the top layer is an ultra-wide bandgap perovskite Cs0.25FA0.6MA0.15Pb(I0.43Br0.57)3 with a bandgap of 1.93 electron volts, which was the main source of stability problems.
To prevent phase segregation in the perovskite, Tan and his team introduced the organic salt 1,4-phenylenediamine dihydroiodide (PEDAI). This additive forms strong bonds with the crystal structure, increasing the ion migration barrier and promoting greater layer uniformity. Additionally, PEDAI molecules occupy voids and bind with lead ions, reducing the number of defects within the perovskite. The surface of the layer was also treated with another organic salt—3MTPAI, which helped reduce the number of grain boundary defects and improved electron transport.
Ultimately, a device with an efficiency of 26.18 percent was obtained, confirmed by independent examination, and a record voltage of 3.15 volts. Although this efficiency is currently lower than that of two-layer tandems reaching 35.5 percent this month, the authors expect rapid growth in efficiency in the coming years. Regarding stability, the devices showed respectable results, retaining 96 percent of initial efficiency after 1500 hours of continuous operation. There is a hypothesis that the salt additives proposed by Tan could also be applied to improve the stability of standard two-layer tandems.
