Research Of Buffer Layers Of P3HT-based Polymer Solar Cells

A strategy to improve the performance of polymer solar cells (PSCs) is to add interfacebuffer layers between the photoactive layer and the electrodes. This thus requires cheap,solution processable, safe and environmental friendly buffer layer materials for the practicalapplication of PSCs.According to the selective transmission ability to different carriers, theinterface layers can be divided into hole transport layer (HTL) and electron transport layer(ETL), respectively. In this paper, we focused on these two buffer layers and carried out thefollowing works for the purpose of enhance the power conversion efficiency (PCE) of PSCs:(1) Modified graphite oxide (GO) films with small organic molecules containing-OSO3H groups, and then used as hole transport layer materials with the simple method ofspin coating. The modification enhanced hole transport ability of GO and improved theperformance P3HT: PCBM-based PSCs significantly. We first modified GO surface withdifferent concentrations of1-pyrene sulfonic acid (PSA). PSA with suitable thickness wasfound to improve conductivity of GO film and enhance the proton exchange interactionbetween GO and the polymer of active layer. Then four small molecules, i.e.p-toluenesulfonic acid (TSA), benzene sulfonic acid (BSA),2-naphthalenesulfonic acid(NSA) and PSA were used to modify GO as hole transport layers. TSA, BSA, PSA improvedthe PCE of the PSCs by55.5%,50.0%,38.5%, but NSA reduced the PCE by16.0%. Testresults proved that the surface morphology and wettability of GO films changed aftermodification with different small molecules. The different conjugation effect in the benzenering and distinct solubility was the main cause of the diverse performance of PSCs.(2) We introduced two common guanidinium into P3HT: ICBA-based PSCs with simplespin coating method, and proved that guanidine hydrochloride and guanidine nitrate weregood electronic transport layer materials, significantly enhancing the performance of thePSCs. The PCE increased by11.9%with guanidine hydrochloride, and29.7%withguanidine nitrate. We speculated that a strong interaction happened between Al and theunpaired electrons in guanidinium, and an interface dipole layer formed between theelectrode and the active layer. These phenomena could promote the electronic transmissionand collection, and effectively prevent the diffusion of Al atoms into the active layer as well as, which was helpful for the improvement of the PSCs’performance.