# Novel Gradient p-Doping Strategy Enables Efficient Carbon-Based Hole Transport Layer-Free Perovskite Solar Cells

## TL;DR

A new method for improving perovskite solar cells by creating a gradient p-doping profile is developed, leading to higher efficiency and stability without a hole transport layer.

## Contribution

The first demonstration of gradient p-doping in printable mesoscopic perovskite solar cells using a novel polymer additive.

## Key findings

- A polymer additive creates a spontaneous gradient p-doping profile in mesoporous perovskite solar cells.
- The optimized solar cells achieved 21.56% power conversion efficiency and over 1500 hours of stability at 55°C.
- Device simulations and photoluminescence mapping confirmed improved hole transport and voltage performance.

## Abstract

A novel strategy of creating spontaneous formation of gradient p-doping in perovskite embedded in mesoporous oxide scaffold is developed.The feasibility of implementing a gradient p-doping strategy in printable mesoscopic perovskite solar cells is demonstrated for the first time through combined device simulations and cross-sectional photoluminescence mapping.The resulting carbon-based hole transport layer-free solar cell exhibits outstanding power conversion efficiency along with superior operational stability over 1500 h without UV filter at 55 °C.

A novel strategy of creating spontaneous formation of gradient p-doping in perovskite embedded in mesoporous oxide scaffold is developed.

The feasibility of implementing a gradient p-doping strategy in printable mesoscopic perovskite solar cells is demonstrated for the first time through combined device simulations and cross-sectional photoluminescence mapping.

The resulting carbon-based hole transport layer-free solar cell exhibits outstanding power conversion efficiency along with superior operational stability over 1500 h without UV filter at 55 °C.

The online version contains supplementary material available at 10.1007/s40820-026-02112-z.

Carbon-based hole transport layer-free (HTL-free) printable mesoscopic perovskite solar cells (p-MPSCs) are highly attractive for their low-cost and scalable fabrication. However, the intrinsically n-type nature of the perovskite, combined with the lack of an HTL, severely impedes hole extraction and limits device performance. In this work, we innovatively introduce a polymer with strong electron-withdrawing capability as an additive into p-MPSCs. Owing to its large molecular size, this polymer spontaneously forms a negative gradient distribution from top to bottom within the mesoporous scaffold during fabrication. This distribution creates a favorable gradient p-doping profile within p-MPSCs, which facilitates more efficient hole transport, a finding corroborated by combined device simulation and cross-sectional photoluminescence mapping. Consequently, the optimized p-MPSCs exhibit an average open-circuit voltage enhancement of over 50 mV, a steady-state power conversion efficiency of 21.56% and operational stability exceeding 1500 h at 55 °C under simulated 1-sun illumination using a halogen lamp without a UV filter.

The online version contains supplementary material available at 10.1007/s40820-026-02112-z.