Role and Function of Polymer Binder Thickeners in Carbon Pastes for Multiporous-Layered-Electrode Perovskite Solar Cells

To fabricate fully printed carbon-based multiporous-layered-electrode perovskite solar cells (MPLE-PSCs), a polymer binder thickener had to be added to the carbon paste for the conductive carbon electrode. The polymer binder thickener is a key material to control the dispersion of carbon particles, viscosity for screen printing, and thickness and porosity of carbon electrodes. In this work, the role and effect of polymer binder thickeners for high-temperature carbon porous electrodes on MPLE-PSCs have been investigated in detail. Several carbon pastes with/without polymer binder thickeners (4 types of ethyl cellulose and 2 types of hydroxypropyl cellulose, which have different viscosities) were compared. What we understand in this paper are (1) Aggregation and dispersion of carbon particles are controlled by the polymer binder thickener (ethyl cellulose and/or hydroxypropyl cellulose); (2) For the porous carbon electrodes, the polymer binder thickeners are carbonized during the sintering procedure at 400 degrees C and can be kept on the surface of carbon particles as the additional carbon surface skin, which improves the conductivity; (3) The polymer binder thickeners can help the formation of a fine mesoporous structure in the annealed carbon electrodes. Combinations of results between viscosity, thermal, and specific surface area analyses revealed the close relationship between device performance and printability, dispersibility, and porosity brought by the polymer binder thickeners. As a result, the addition of a 20 wt % polymer binder thickener improved the average power conversion efficiency (PCE) from 9.52 +/- 2.04 to 10.86 +/- 0.85%, achieving a champion PCE of 12.06%.