As the record single-junction efficiencies of perovskite solar cells now rival those of CIGS, CdTe, and multicrystalline silicon, they are becoming increasingly attractive for use in tandem solar cells, due to their wide, tunable bandgap and solution processability. Previously, perovskite/silicon tandems were limited by significant parasitic absorption and poor environmental stability. Here, we improve the efficiency of monolithic, two-terminal, 1 cm 2 perovskite/silicon tandems to 23.6% by combining an infrared-tuned silicon heterojunction bottom cell with the recently developed cesium formamidinium lead halide perovskite. This more stable perovskite tolerates deposition of a tin oxide buffer layer via atomic layer deposition that prevents shunts, has negligible parasitic absorption, and allows for the sputter deposition of a transparent top electrode. Furthermore, the window layer doubles as a diffusion barrier, increasing the thermal and environmental stability to enable perovskite devices that withstand a 1000-hour damp heat test at 85 °C and 85% relative humidity.

Wide–band gap metal halide perovskites are promising semiconductors to pair with silicon in tandem solar cells to pursue the goal of achieving power conversion efficiency (PCE) greater than 30% at low cost. However, wide–band gap perovskite solar cells have been fundamentally limited by photoinduced phase segregation and low open-circuit voltage. We report efficient 1.67–electron volt wide–band gap perovskite top cells using triple-halide alloys (chlorine, bromine, iodine) to tailor the band gap and stabilize the semiconductor under illumination. We show a factor of 2 increase in photocarrier lifetime and charge-carrier mobility that resulted from enhancing the solubility of chlorine by replacing some of the iodine with bromine to shrink the lattice parameter. We observed a suppression of light-induced phase segregation in films even at 100-sun illumination intensity and less than 4% degradation in semitransparent top cells after 1000 hours of maximum power point (MPP) operation at 60°C. By integrating these top cells with silicon bottom cells, we achieved a PCE of 27% in two-terminal monolithic tandems with an area of 1 square centimeter.

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Grain engineering through combined MACl and MAH 2 PO 2 additives in perovskite precursors improves the photovoltaic performance of perovskite/silicon tandem cells. MACl increases the grain size of wide-bandgap perovskite films and also produces smooth films. MAH 2 PO 2 suppresses non-radiative recombination sites at grain boundaries. The synergetic effects of MACl and MAH 2 PO 2 further promote grain growth and prolong the carrier recombination lifetime. This enables a power conversion efficiency of 25.4% for a perovskite/silicon tandem device. SUMMARYOrganic-inorganic halide perovskites are promising semiconductors to mate with silicon in tandem photovoltaic cells due to their solution processability and tunable complementary bandgaps. Herein, we show that a combination of two additives, MACl and MAH 2 PO 2 , in the perovskite precursor can significantly improve the grain morphology of wide-bandgap (1.64-1.70 eV) perovskite films, resulting in solar cells with increased photocurrent while reducing the open-circuit voltage deficit to 0.49-0.51 V. The addition of MACl enlarges the grain size, while MAH 2 PO 2 reduces non-radiative recombination through passivation of the perovskite grain boundaries, with good synergy of functions from MACl and MAH 2 PO 2 . Matching the photocurrent between the two subcells in a perovskite/silicon monolithic tandem solar cell by using a bandgap of 1.64 eV for the top cell results in a high tandem V oc of 1.80 V and improved power conversion efficiency of 25.4%.

A new monolithic perovskite/silicon tandem solar cell architecture is proposed based on double-side-textured silicon cells with sub-micrometer pyramids. These pyramids are rough enough to scatter light within silicon nearly as efficiently as large pyramids but smooth enough to solution process a perovskite film. A bladecoated perovskite film planarizes the textured silicon cell. With a textured lightscattering layer added to the top to reduce front-surface reflectance, a monolithic perovskite/silicon tandem cell reaches an efficiency of 26%.