Back interface engineering by designing core–shell structured mesoporous carbon spheres counter electrode in thin–film solar cells

Exploration of economical and highly effective counter electrodes is crucial for both fundamental research into and the commercial application of dye-sensitized solar cells (DSCs) and perovskite solar cells (PSCs). Herein, a new type of core–shell structured mesoporous carbon spheres (Ag@MCSs) was meticulously designed and synthesized as a low-cost counter electrode to optimize back interface. The tailored mesoporous core–shell structure and metal nanoparticle core can optimize the energy level alignment and improve the conductivity of the counter electrode. These improvements facilitate charge carrier extraction and transport processes and inhibit recombination at the back interface of the counter electrode/perovskite. The hole transport layer–free PSCs using Ag@MCSs counter electrode obtains a power conversion efficiency (PCE) of 12.36 %, surpassing the parallel PSCs based on smooth surface carbon spheres (SSCSs) and micro/mesoporous carbon spheres (MMCSs) counter electrodes. Additionally, Ag@MCSs provide numerous catalytically active sites, smooth mass transfer channels, and improved conductivity, resulting in superior catalytic activity for iodide redox couple regeneration in DSCs, generating a high PCE of 8.25 %. This study is expected to offer a feasible pathway for exploring cheap counter electrodes and back interface engineering to accelerate mass and carrier transport processes in the back interface of PSCs and DSCs.