The paper reports the development of a 2D p-n junction diode based on electrostatically doped tungsten diselenide (WSe₂) monolayers. This device is a significant advancement in 2D optoelectronics, as p-n diodes are fundamental components in various optoelectronic devices. The authors demonstrate the diode's applications in photovoltaic solar cells, photodiodes, and light-emitting diodes. Key findings include: 1. **Device Fabrication and Characterization**: The device is fabricated using split gate electrodes to form a p-n junction in WSe₂ monolayers. The monolayer thickness is confirmed through photoluminescence (PL) and Raman spectroscopy, ensuring efficient electrically driven light emission. 2. **Electrical Characteristics**: The device exhibits clear ambipolar transfer characteristics, allowing both electrons and holes to be injected into the channel. The diode parameters, such as saturation current and ideality factor, are determined using the Shockley diode equation. 3. **Solar Energy Conversion**: The device operates as a photovoltaic solar cell, achieving a maximum power conversion efficiency of approximately 0.5%. This efficiency is comparable to that of conventional bulk WSe₂ p-n junctions. 4. **Photodiode Operation**: The device can also function as a photodiode, showing a photocurrent of 29 pA at -1 V, corresponding to a photoresponsivity of 16 mA/W. 5. **Electroluminescence**: The device emits light through the p-n junction, with an electroluminescence efficiency of approximately 0.1%. The emission spectrum peaks at 1.547 eV, shifted from the monolayer PL due to different dielectric environments. 6. **Future Applications**: The authors envision the potential of 2D atomic crystals in low-cost, flexible, and semi-transparent solar cells, as well as in lighting units and transparent, flexible displays. The study highlights the promise of 2D atomic crystals in optoelectronics, particularly in solar energy conversion and light emission, and suggests that large-scale production of these materials could significantly impact future technologies.The paper reports the development of a 2D p-n junction diode based on electrostatically doped tungsten diselenide (WSe₂) monolayers. This device is a significant advancement in 2D optoelectronics, as p-n diodes are fundamental components in various optoelectronic devices. The authors demonstrate the diode's applications in photovoltaic solar cells, photodiodes, and light-emitting diodes. Key findings include: 1. **Device Fabrication and Characterization**: The device is fabricated using split gate electrodes to form a p-n junction in WSe₂ monolayers. The monolayer thickness is confirmed through photoluminescence (PL) and Raman spectroscopy, ensuring efficient electrically driven light emission. 2. **Electrical Characteristics**: The device exhibits clear ambipolar transfer characteristics, allowing both electrons and holes to be injected into the channel. The diode parameters, such as saturation current and ideality factor, are determined using the Shockley diode equation. 3. **Solar Energy Conversion**: The device operates as a photovoltaic solar cell, achieving a maximum power conversion efficiency of approximately 0.5%. This efficiency is comparable to that of conventional bulk WSe₂ p-n junctions. 4. **Photodiode Operation**: The device can also function as a photodiode, showing a photocurrent of 29 pA at -1 V, corresponding to a photoresponsivity of 16 mA/W. 5. **Electroluminescence**: The device emits light through the p-n junction, with an electroluminescence efficiency of approximately 0.1%. The emission spectrum peaks at 1.547 eV, shifted from the monolayer PL due to different dielectric environments. 6. **Future Applications**: The authors envision the potential of 2D atomic crystals in low-cost, flexible, and semi-transparent solar cells, as well as in lighting units and transparent, flexible displays. The study highlights the promise of 2D atomic crystals in optoelectronics, particularly in solar energy conversion and light emission, and suggests that large-scale production of these materials could significantly impact future technologies.