Spontaneous Assembly of Bilayer Perovskite Crystals for Built-In P-N Homojunction

Abstract

Developing sufficient dynamics for charge separation and transfer is a critical issue in photovoltaic performance. Normally, the dynamics can be improved by band bending via surface engineering but negligible in the p-n homojunction for boosted perovskite solar cells (PSCs). Herein, we adopted novel carbon dots (CDs) as addition to induce bilayer p-n perovskite homojunction to improve interfacial charge transfer kinetics in n-i-p PSCs. Notably, the CDs addition induces the spontaneous assembly of a bilayer structure with the CDs-enriched upper and pristine underlying perovskite layers, which causes a formation of p-n homojunction with a built-in electric field to modulate energy levels, promoting charge separation and transfer. Benefiting from the p-n homojunction, the power conversion efficiency (PCE) of PSCs remarkably increased from 18.57% to an impressive 21.09%. Additionally, the hydrophobic nature of the CDs considerably prolongs the lifespan of PSCs, with the efficiency preserving 90% of its original value even after being exposed to humid air for 1400 hours.

Keywords: p-n homojunction, carbon dots, perovskite bilayer, charge recombination, energy level