Phosphorus-Doped Carbon Nitride Solid: Enhanced Electrical Conductivity and Photocurrent Generation

TLDR

Graphitic carbon nitride (g‑C3N4) is a thermally stable polymeric semiconductor with promising photovoltaic potential, but its efficiency is limited by band‑gap absorption. The study aims to enhance g‑C3N4 performance by introducing phosphorus heteroatoms through a structural doping strategy. Phosphorus atoms were incorporated into g‑C3N4 via polycondensation of carbon‑nitride precursors with a phosphorus source derived from 1‑butyl‑3‑methylimidazolium hexafluorophosphate ionic liquid. The doped material retained its structural integrity while exhibiting a four‑order‑of‑magnitude increase in electrical conductivity and up to five‑fold higher photocurrent, making it attractive for solar cells, batteries, and catalysis.

Abstract

As a new kind of polymeric semiconductors, graphitic carbon nitride (g-C3N4) and its incompletely condensed precursors are stable up to 550 °C in air and have shown promising photovoltaic applications. However, for practical applications, their efficiency, limited e.g. by band gap absorption, needs further improvement. Here we report a "structural doping" strategy, in which phosphorus heteroatoms were doped into g-C3N4 via carbon sites by polycondensation of the mixture of the carbon nitride precursors and phosphorus source (specifically from 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid). Most of the structural features of g-C3N4 were well retained after doping, but electronic features had been seriously altered, which provided not only a much better electrical (dark) conductivity up to 4 orders of magnitude but also an improvement in photocurrent generation by a factor of up to 5. In addition to being active layers in solar cells, such phosphorus-containing scaffolds and materials are also interesting for polymeric batteries as well as for catalysis and as catalytic supports.