From Defects to Devices: Design Guidelines for High-Performance Diamond-Based Solar Cells and Single-Dopant Diodes

Abstract: This work establishes key technological guidelines for designing diamond-based optoelectronic devices, derived from a first-principles investigation of two architectures: a PIN junction with a boron-vacancy-boron (BVB) intermediate-band absorber, and a PN junction based on phosphorus-vacancy (PV) defects. For the PIN solar cell, practical design principles include: i) aligning incident light in the xz-plane to exploit anisotropic absorption; ii) using graded junctions to mitigate tunnelling losses at abrupt interfaces; iii) targeting an absorber thickness of ~500 nm to balance absorption and carrier extraction; and iv) leveraging the high transparency of both contact layers for bifacial device configurations. For the PN diode, the PV-doped diamond operates via impurity-band conduction, making it suitable for degenerate p-type applications such as tunnel diodes or asymmetric junctions, while its temperature-dependent Seebeck anisotropy and sign-reversal offer opportunities for thermal management applications. When paired with phosphorus-doped n-type regions, these defects enable single-dopant junctions that significantly simplify device manufacturing. Using density functional theory with GW corrections, Bethe-Salpeter equation calculations and carrier transport modelling coupled to device electrostatics via a Poisson solver, we show that the BVB defect introduces intermediate bands without degrading diamond's high carrier mobility or thermal conductivity, while PV-doping provides high conductivity at room temperature through impurity-band transport. Overall, both defect-engineered systems preserve diamond's superior transport and thermal properties even after doping, offering viable pathways for high-performance diamond optoelectronics. These guidelines provide a practical foundation for fabricating efficient diamond-based photovoltaic and diode devices.