Efficient and Flexible Perovskite Solar Cell Based on Inverted-Nanocone Structure with Enhanced Mechanical Properties

Abstract

Organohalide lead perovskite materials have attracted tremendous attention because of their high mobility, excellent absorption, long diffusion length, and low-cost fabrication process. These features make them ideal candidates for solar cell devices with power conversion efficiency (PCE) up to 21%. Nowadays, the integration of solar cell devices with nanostructures becomes a new strategy to improve the device performance by enhancement of the light absorption and carriers collection. In fact, the nanostructured substrates can improve not only the performance of device but also the device mechanical robustness and reliability, which are beneficial for flexible devices. Herein, we report an efficient, flexible and mechanically robust-perovskite solar cell using inverted-nanocone (i-cone) plastic. Firstly, a facile and novel solution process is introduced to fabricate UV-cured epoxy substrate with i-cone pattern. Then, in order to deposit a uniform and conformal layer of perovskite on i-cone substrate, a two-step evaporation process is employed. The results of photovoltaic measurement show that the device based on i-cone has a PCE of 11.29%, which is 37% higher than the device on flat substrate. Furthermore, the device on i-cone with aspect-ratio-0.5 demonstrates the highest current density and PCE that is supported by UV-visible and external quantum efficiency tests. More interestingly, the results of bending test illustrate that the efficiency of textured device remains more than 90% of the initial value after 200 mechanical bending cycles, which is remarkably higher than flat device, which degrades down to only 60% in the same condition. To further study the effect of nanostructures on the device performance and mechanical robustness, the finite element mechanical modeling was carried out. The simulation results combined with SEM images demonstrate that the i-cone device relaxes the stress and strain upon device bending more efficient than its counterpart, which suppresses crack nucleation and propagation in different layers of a perovskite solar cell. Also, the top-view SEM images of devices after bending cycles have supported the simulation results. This essentially leads to much improved device reliability and robustness and will have significant impact on practical applications.