Improved performance of perovskite solar cells using conjugated polymer-graphene oxide as the passivation material

Abstract

Organic-inorganic hybrid perovskite solar cells (PSCs) have achieved power conversion efficiency (PCE) from 3.8% to 25.2% in recent years. However, the charge transport ability of the transporting layers and the quality of crystalline films limit further development of PSCs. To fabricate highly efficient PSCs, effective charge transport to electrodes through transporting layers is a necessary requirement. Suitable interface engineering is very critical because it can not only benefit the charge extraction and transport, but also effectively passivate the traps on the surface and grain boundary of the perovskite. It has been shown that the passivation layer for the perovskite plays a vital role in the performance of PSCs. The close fit between the charge transport layer and the perovskite layer is required to reduce the interfacial recombination and accelerate the carrier extraction and collection. Besides, the appropriate passivation layer has a potential impact on the crystallization and the morphology of the perovskite film. To achieve high-performance devices, it is crucial to design an effective passivation layer with appropriate nanomaterials. In this work, we synthesized poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene] (MOPPV) on few-layer graphene oxide (GO) by in situ polymerization at room temperature. MOPPV-GO can fully combine the advantages of the two materials. The novel nanocomposite MOPPV-GO is used as the ultra-thin passivation layer of PSCs, of which the structure is ITO/TiO2/(FAPbI3) x (MAPbCl3)1– x /MOPPV-GO/spiro-OMeTAD/Ag. Since the surface morphology of the perovskite layer would affect the performance of devices significantly, the perovskite films with and without the passivation layer by atomic force microscopy is found that the MOPPV-GO can facilitate the growth of perovskite crystal with larger grains and enhance the quality of perovskite films. The root mean square roughness values of the perovskite films with and without MOPPV-GO were evaluated to be 19.87 and 25.85 nm, justifying the improvement of the surface flatness of the perovskite film with the decoration of MOPPV-GO, which would enhance the contact and carrier transport between the hole transport layer and the perovskite layer. As a result, the PSCs with MOPPV-GO exhibited considerably low hysteresis indices (0.02) and showed a short circuit current density of 23.54 mA cm–1, an open circuit voltage of 1.09 V, and a fill factor of 76.46%, corresponding to a high power conversion efficiency of 19.73%. By contrast, the control PSCs without MOPPV-GO showed a high hysteresis index of 0.18, with a poor power conversion efficiency of 16.42%. Meanwhile, it is shown that the EQE curve of MOPPV-GO modified PSC is higher than that of unmodified devices, which is consistent with the experimental results of J-V curve. The steady-state power output of various devices in ambient conditions under continuous AM 1.5G illumination was tested, which shows excellent stability of the PSC with MOPPV-GO during the period of 1000 s, indicating the positive contribution of MOPPV-GO interlayer to the stability. This work could provide a new idea for the synthesis and application of graphene-based materials in solar cells.