# Positive Feedback Organic‐on‐Silicon Upconversion Devices

## TL;DR

This paper introduces a hybrid optoelectronic device that efficiently converts near-infrared light to visible light, with potential applications in imaging and electronics.

## Contribution

The novel contribution is a hybrid device architecture combining OLEDs and Si photodiodes to achieve high upconversion gain and bistability.

## Key findings

- The device upconverts near-infrared light (1050 nm) to visible light (570 nm) with a photon-to-photon gain of up to 900%.
- Minimizing photodiode capacitance improves the device's response speed.
- Electrical crosstalk in pixelated devices must be addressed to avoid unintended cascading activation.

## Abstract

Positive feedback upconversion devices exhibit optoelectronic bistability and large photon‐to‐photon gain that can benefit applications ranging from night vision to neuromorphic image classification. Here, a hybrid device architecture is introduced that integrates a tandem organic light‐emitting diode (OLED) on top of an organic/Si heterojunction photodiode. These devices respond to near infrared light at wavelengths up λ ≈ 1.1 µm and exhibit a peak photon‐to‐photon upconversion gain of 9x when triggered with input light intensity <1 µW cm−2. It is found that minimizing the capacitance of the photodiode is important for maximizing the upconversion response speed of the device, and that electrical crosstalk in pixelated devices must be overcome to prevent cascading effects where one activated pixel triggers many others. These results mark an important step for optoelectronic upconverters that can be integrated with Si microelectronics, and they establish a path to extend the responsivity further into the near infrared by moving to other inorganic semiconductor platforms such as Ge or InGaAs.

Positive optoelectronic feedback is achieved by depositing a tandem OLED on top of a heterojunction Si photodiode. The resulting hybrid device is bistable and upconverts near‐infrared light (λ = 1050 nm) to visible light (λ = 570 nm) with a photon‐to‐photon upconversion yield of up to 900%.