Forward‐Biased Perovskite Photodiodes for In‐Sensor Optical Change Sensing

ABSTRACT Conventional imaging sensors acquire absolute optical intensity from entire scenes, including redundant background information that must be read out, digitized, transferred, and processed, resulting in substantial front‐end data overhead. Here, we introduce a forward‐bias current‐balancing operation in a perovskite photodiode that directly encodes reference‐relative optical changes through an electrically programmable zero‐output reference. In this operation, the forward‐bias current serves as a tunable counter‐current that compensates the photocurrent at a selected optical reference, enabling optical changes below and above the reference to be converted into output currents with opposite polarities. Leveraging the large photovoltage, efficient charge extraction, and negligible bias‐induced hysteresis of the perovskite solar cell architecture, the device provides a suitable platform for reference‐relative optical encoding under forward bias. Based on this principle, subtract‐type global light adaptation is demonstrated to compensate background‐induced offset currents while preserving image contrast, alongside pixel‐wise scene change detection that directly visualizes deviations from a programmed reference scene. These results establish forward‐bias current balancing as a new framework for sensor‐level optical‐change encoding and analog front‐end preprocessing prior to readout, analog‐to‐digital conversion, and downstream processing, without requiring additional preprocessing circuitry.