Wavelength‐Recognizable SbSI:Sb 2 S 3 Photovoltaic Devices: Elucidation of the Mechanism and Modulation of their Characteristics

The output of photovoltaic (PV) devices is mostly independent of the wavelength of the incident light, whereas an anomalous wavelength‐dependent photovoltaic effect (WDPE) has recently been observed in antimony chalcohalide‐chalcogenide (SbSI:Sb 2 S 3 ) PVs. Remarkably, the open‐circuit voltage ( V OC ) exhibits a reversible change between low V OC for short wavelengths and high V OC for long wavelengths. Herein, this work presents i) insights into the underlying mechanisms of this phenomenon by electron spin resonance (ESR) measurements and ii) the switchable character of WDPE depending on the hole transport material (HTM). Operando ESR measurements with light irradiation revealed that the hole density in the HTM is significantly suppressed when the ultraviolet component is included in the irradiation light. This indicated interfacial charge recombination rather than hole transfer to the HTM under short‐wavelength light irradiation, providing a basis for understanding the mechanism of WDPE. Furthermore, the use of poly(triarylamine) as the HTM unexpectedly exhibit the opposite wavelength‐ V OC dependence, where a low V OC is observed with long‐wavelength light. In addition, the introduction of a polar gas accelerated the response speed of these effects. These findings shed light on the expansion of unique wavelength‐responsive single junction devices.