Biao Shi

Semitransparent solar cells (ST-SCs) have received great attention due to their promising application in many areas, such as building integrated photovoltaics (BIPVs), tandem devices, and wearable electronics. In the past decade, perovskite solar cells (PSCs) have revolutionized the field of photovoltaics (PVs) with their high efficiencies and facile preparation processes. Due to their large absorption coefficient and bandgap tunability, perovskites offer new opportunities to ST-SCs. Here, a general overview is provided on the recent advances in ST-PSCs from materials and devices to applications and some personal perspectives on the future development of ST-PSCs.

SnO2 is widely used and one of the most efficient electron transport layers in perovskite solar cells (PSCs). However, SnO2 films often contain detrimental defects and may also have mismatches in energy level alignment with perovskite films, thus limiting the open-circuit voltage (VOC). Managing the defects and band structure are critical to reduce energy loss in PSCs. Herein, cobalt chloride hexahydrate (CoCl2·6H2O) is introduced into a SnO2 film, which shows favorable energy level alignment and better charge extraction. Correspondingly, an enhanced VOC up to 1.20 V was achieved along with an efficiency of 23.82%, which is the record open-circuit voltage at the optical band gap of 1.54 eV in planar structure PSCs. Moreover, the target devices show enhanced stability, which retains 83.5% of their initial efficiencies after 200 h under continuous irradiation. The doping method provides an effective strategy for reducing energy loss to further enhance the efficiency of PSCs.

Potentially temperature-resistant inorganic perovskite/silicon tandem solar cells (TSCs) are promising devices for boosting efficiency past the single-junction silicon limit. However, undesirable non-radiative recombination generally leads to a significant voltage deficit. Here, we introduce an effective strategy using nickel iodide, an inorganic halide salt, to passivate iodine vacancies and suppress non-radiative recombination. NiI2-treated CsPbI3-xBrx inorganic perovskite solar cells with a 1.80 ​eV bandgap exhibited an efficiency of 19.53% and a voltage of 1.36 ​V, corresponding to a voltage deficit of 0.44 ​V. Importantly, the treated device demonstrated excellent operational stability, maintaining 95.7% of its initial efficiency after maximum power point tracking for 300 ​h under continuous illumination in a N2 atmosphere. By combining this inorganic perovskite top cell with a narrower bandgap silicon bottom cell, we for the first time achieved monolithic inorganic perovskite/silicon TSCs, which exhibited an efficiency of 22.95% with an open-circuit voltage of 2.04 ​V. This work provides a promising strategy for using inorganic passivation materials to achieve efficient and stable solar cells.

Abstract The perovskite/silicon tandem solar cell (PK/c‐Si TSC) is a reasonable choice that can break through the efficiency limitations of silicon cells. Here, the p‐i‐n perovskite solar cell is conformally grown by the evaporation–solution combination technique on fully‐textured silicon heterojunction cells to realize two‐terminal PK/c‐Si TSCs. Due to the adverse effect of the residual PbI 2 at the bottom of the perovskite bulk on device performance, a thermal‐evaporated CsBr thin layer is introduced between the perovskite layer and the hole transport layer to construct a gradient perovskite absorber for optimized energy level alignment, so as to improve the open‐circuit voltage and fill factor of the device. Finally, the PK/c‐Si tandem cell achieves an efficiency of 27.48% and is stable in nitrogen over 10 000 h.

Mixed lead–tin (Pb–Sn) perovskite photovoltaics have attracted great attention for reducing toxic lead and tuning optical bandgaps. However, the main challenges are the uncontrolled crystallization rate of perovskite films and easy oxidation of Sn2+, which can give rise to rough morphology and unwanted p-type doping. Herein, we precisely modulated the crystallization process of the mixed Pb–Sn perovskite by adjusting the energy barrier of nucleation with the help of caffeic acid (CA), a natural antioxidant, which is introduced into the perovskite precursor solution. We demonstrated CA also could depress the oxidation of Sn2+ to Sn4+ effectively by reducing hydroxyl functional groups, leading to the reduction of background carriers and hole trap densities. Therefore, an efficiency of 19.85% was obtained with an impressive open-circuit voltage of 0.855 V for mixed Pb–Sn perovskite solar cells with high reproducibility.