All existing solar cell materials including hybrid perovskites show rather small absorption coefficient (α) of ≈104 cm−1 in the bandgap (Eg) transition region. The weak band‐edge light absorption is an essential problem, limiting conversion efficiency particularly in a tandem solar cell. Herein, all distorted chalcogenide perovskites (BaZrS3, SrZrS3, BaHfS3, and SrHfS3) are found experimentally to exhibit extraordinary high α exceeding 105 cm−1 near Eg, indicating the highest band‐edge α among all known solar cell materials. The giant absorption in the Eg region, which is consistent with the first principles, arises from the intense p–d interband transition enabled by dense S 3p valence states. For solar cell application, low‐gap BaZrS3 derivatives, Ba(Zr,Ti)S3 and BaZr(S,Se)3, are further synthesized. Among the possible candidates of top‐cell materials, an earth‐abundant and nontoxic Ba(Zr,Ti)S3 alloy shows great potential, reaching a maximum potential efficiency exceeding 38% in a chalcogenide perovskite/crystalline Si tandem architecture.

Optical color sensors based on perovskites are described. These sensors overcome the limits of conventional image sensors used in smartphones and digital cameras. The sensors allow for detecting the primary colors red, green, and blue without using optical filters. The color sensors consist of vertically stacked diodes using perovskite alloys. The described sensor structure is color aliasing or color moiré error free, while conventional sensors using optical filters are limited by this error. The spectral sensitivity of vertically stacked sensors is up to three times higher than the spectral sensitivity of filter‐based color sensors. The optical constants of the required perovskite alloys are determined, and color sensors are electromagnetically modeled. The spectral sensitivities of the sensors are colorimetrically characterized and compared to sensors in the literature including conventional sensors using optical filters. This study, for the first time, shows that a vertically stacked three color sensor exhibits a color error equal to, or smaller than, errors of conventional sensors using optical filters. Details on the used materials, the device design, and the colorimetric analysis are provided.

Color image sensing by a smartphone or digital camera employs sensor elements with an array of color filters for capturing basic blue, green, and red color information. However, the normalized optical efficiency of such color filter-based sensor elements is limited to only one-third. Optical detectors based on perovskites are described, which can overcome this limitation. An efficient color sensor design has been proposed in this study that uses a vertically stacked arrangement of perovskite diodes. As compared to the conventional color filter-based sensors, the proposed sensor structure can potentially reach normalized optical efficiency approaching 100%. In addition, the proposed sensor design does not exhibit color aliasing or color Moiré effects, which is one of the main limitations for the filter-based sensors. Furthermore, up to our knowledge, for the first time, it could be theoretically shown that both vertically arranged sensor and conventional color filter-based sensor provide almost comparable color errors. The optical properties of the perovskite materials are determined by optical measurements in combination with an energy shift model. The optics of the stacked perovskite sensors is investigated by threedimensional finite-difference timedomain simulations. Finally, colorimetric characterization was carried out to determine the color error of the sensors.

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The Shockley and Queisser limit, a well-known efficiency limit for a solar cell, is based on unrealistic physical assumptions and its maximum limit is seriously overestimated.To understand the power loss mechanisms of record-efficiency cells, a more rigorous approach is necessary. Here, we have established a formalism that can accurately predict absolute performance limits of solar cells in conventional thin film form. In particular, a formulation for a strict evaluation of the saturation current in a nonblackbody solar cell has been developed by taking incident angle, light polarization and texture effects into account. Based on the established method, we have estimated the maximum efficiencies of 13 well-studied solar cell materials [GaAs, InP, CdTe, a-HC(NH 2 ) 2 PbI 3 ] in a 1-µm-thick physical limit. Our calculation shows that over 30% efficiencies can be achieved for absorber layers with sharp absorption edges (GaAs, InP, CdTe, CuInGaSe 2 , Cu 2 ZnGeSe 4 ). Nevertheless, many record-efficiency polycrystalline solar cells, including hybrid perovskites, are limited by open-circuit voltage and fill-factor losses. We show that the maximum conversion efficiencies described here present alternative limits that can predict the power generation of real-world solar cells. *fujiwara@gifu-u.ac.jp sc J kT qV J J −  