Pinning energies of organic semiconductors in high-efficiency organic solar cells

With the emergence of new materials for high-efficiency organic solar cells(OSCs),understanding and finetuning the interface energetics become increasingly important.Precise determination of the so-called pinning energies,one of the critical characteristics of the material to predict the energy level alignment(ELA)at either electrode/organic or organic/organic interfaces,are urgently needed for the new materials.Here,pinning energies of a wide variety of newly developed donors and nonfullerene acceptors(NFAs)are measured through ultraviolet photoelectron spectroscopy.The positive pinning energies of the studied donors and the negative pinning energies of NFAs are in the same energy range of 4.3−4.6 eV,which follows the design rules developed for fullerene-based OSCs.The ELA for metal/organic and inorganic/organic interfaces follows the predicted behavior for all of the materials studied.For organic-organic heterojunctions where both the donor and the NFA feature strong intramolecular charge transfer,the pinning energies often underestimate the experimentally obtained interface vacuum level shift,which has consequences for OSC device performance.

Self-assembled monolayer modified copper(Ⅰ) iodide hole transport layer for efficient polymer solar cells

The morphology of the copper iodide （CuI） film as an inorganic p-type material has an important influence on enhancing the performance of polymer solar cells （PSCs）. A self-assembled monolayer of 3-aminopropanoic acid （C3-SAM） was used on the surface of indium tin oxide （ITO） before depositing the CuI films. Consequently, a well-distributed and smooth CuI film was formed with pinhole free and complete surface coverage. The root mean square of the corresponding CuI film was reduced from 3.63 nm for ITO/CuI to 0.77 nm. As a result, the average power conversion efficiency （PCE） of PSCs with the device structure of ITO/C3-SAM/CuI/P3HT：PC61BM/ZnO/Al increased significantly from 2.55% （best 2.66%） to 3.04% （best 3.20%） after C3-SAM treatment. This work provides an effective strategy to control the morphology of CuI films through interracial modification and promotes its application in efficient PSCs.