A 2D p-n junction diode based on an electrostatically doped monolayer of tungsten diselenide (WSe₂) is demonstrated, showing potential for optoelectronic applications. The device operates as a photovoltaic solar cell, photodiode, and light-emitting diode (LED). The photovoltaic efficiency is approximately 0.5%, and the electroluminescence efficiency is approximately 0.1%. The device is fabricated using split gate electrodes and is characterized by its ability to generate electric currents and voltages under illumination. The p-n junction is formed by applying opposite voltages to the gate electrodes, enabling rectification behavior. The device exhibits a high ideality factor, indicating significant recombination current, and a fill factor of approximately 0.5. The solar cell achieves a maximum electrical output power of 9 pW at 0.64 V. The device also functions as a photodiode, with a photocurrent of 29 pA at -1 V and a photoresponsivity of 16 mA/W. The device can also emit light, with an electroluminescence efficiency of 0.1%, and the emission peaks at 1.547 eV. The device's performance is compared to conventional bulk WSe₂ p-n junctions, showing comparable efficiency. The device's transparency and flexibility make it suitable for semi-transparent solar cells and flexible displays. The study highlights the potential of 2D atomic crystals for future optoelectronic applications, with the first demonstration of efficient photovoltaic energy conversion in a 2D atomic crystal. The research is supported by the Austrian Science Fund and the European Union. The study also notes two similar studies published during the review process. The device fabrication involves electron beam lithography, metal deposition, and mechanical exfoliation of WSe₂. The device's performance is characterized by I-V measurements, photoluminescence, and electroluminescence. The study provides insights into the electronic properties of WSe₂ and its potential for optoelectronic applications. The results suggest that further improvements in material quality could enhance the device's performance. The study also discusses the potential applications of the device in flexible and semi-transparent solar cells, as well as in valleytronics. The device's performance is analyzed in terms of its electrical characteristics, photovoltaic response, and electroluminescence. The study demonstrates the potential of 2D atomic crystals for future optoelectronic applications, with the first demonstration of efficient photovoltaic energy conversion in a 2D atomic crystal. The study also highlights the importance of material quality and device design in achieving high-performance optoelectronic devices. The research is supported by the Austrian Science Fund and the European Union. The study also notes two similar studies published during the review process. The device's performance is characterized by I-V measurements, photolumA 2D p-n junction diode based on an electrostatically doped monolayer of tungsten diselenide (WSe₂) is demonstrated, showing potential for optoelectronic applications. The device operates as a photovoltaic solar cell, photodiode, and light-emitting diode (LED). The photovoltaic efficiency is approximately 0.5%, and the electroluminescence efficiency is approximately 0.1%. The device is fabricated using split gate electrodes and is characterized by its ability to generate electric currents and voltages under illumination. The p-n junction is formed by applying opposite voltages to the gate electrodes, enabling rectification behavior. The device exhibits a high ideality factor, indicating significant recombination current, and a fill factor of approximately 0.5. The solar cell achieves a maximum electrical output power of 9 pW at 0.64 V. The device also functions as a photodiode, with a photocurrent of 29 pA at -1 V and a photoresponsivity of 16 mA/W. The device can also emit light, with an electroluminescence efficiency of 0.1%, and the emission peaks at 1.547 eV. The device's performance is compared to conventional bulk WSe₂ p-n junctions, showing comparable efficiency. The device's transparency and flexibility make it suitable for semi-transparent solar cells and flexible displays. The study highlights the potential of 2D atomic crystals for future optoelectronic applications, with the first demonstration of efficient photovoltaic energy conversion in a 2D atomic crystal. The research is supported by the Austrian Science Fund and the European Union. The study also notes two similar studies published during the review process. The device fabrication involves electron beam lithography, metal deposition, and mechanical exfoliation of WSe₂. The device's performance is characterized by I-V measurements, photoluminescence, and electroluminescence. The study provides insights into the electronic properties of WSe₂ and its potential for optoelectronic applications. The results suggest that further improvements in material quality could enhance the device's performance. The study also discusses the potential applications of the device in flexible and semi-transparent solar cells, as well as in valleytronics. The device's performance is analyzed in terms of its electrical characteristics, photovoltaic response, and electroluminescence. The study demonstrates the potential of 2D atomic crystals for future optoelectronic applications, with the first demonstration of efficient photovoltaic energy conversion in a 2D atomic crystal. The study also highlights the importance of material quality and device design in achieving high-performance optoelectronic devices. The research is supported by the Austrian Science Fund and the European Union. The study also notes two similar studies published during the review process. The device's performance is characterized by I-V measurements, photolum