# Enhancing π-Delocalization and Suppressing Traps via Doping in Electron Transport Materials for Efficient Semitransparent Organic Photovoltaics

## TL;DR

This paper introduces a new method to improve the efficiency of semitransparent solar cells by enhancing electron transport through chemical doping.

## Contribution

The novel approach involves using LiTFSI to enhance π-delocalization in the electron transport layer, leading to higher efficiency in semitransparent organic photovoltaics.

## Key findings

- LiTFSI doping increases power conversion efficiency to 14.3% in semitransparent organic photovoltaics.
- Doping reduces trap densities and improves conductivity in both the ETL and ultrathin silver electrode.
- The method achieves an average visible transmittance of 29.0% while maintaining high light utilization energy.

## Abstract

High-performance semitransparent organic photovoltaics (STOPVs) with decreased electrical loss were fabricated via introducing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to electron transport layer (ETL).LiTFSI interacts with ETL material PDINN and enhanced π-delocalization in PDINN, which is beneficial to conductivity and thereby electron collection range.LiTFSI-doped PDINN-based STOPVs show an improved power conversion efficiency of 14.3%, average visible transmittance of 29.0%, and light utilization energy of 4.15%, which is among the highest values of optical structure-free STOPVs.

High-performance semitransparent organic photovoltaics (STOPVs) with decreased electrical loss were fabricated via introducing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to electron transport layer (ETL).

LiTFSI interacts with ETL material PDINN and enhanced π-delocalization in PDINN, which is beneficial to conductivity and thereby electron collection range.

LiTFSI-doped PDINN-based STOPVs show an improved power conversion efficiency of 14.3%, average visible transmittance of 29.0%, and light utilization energy of 4.15%, which is among the highest values of optical structure-free STOPVs.

The online version contains supplementary material available at 10.1007/s40820-026-02083-1.

The ultrathin metal electrode in semitransparent organic photovoltaics (STOPVs) usually suffers from limited charge collection capability and conductivity and thus hinders the power conversion efficiency (PCE). Herein, a new strategy of enhancing the π-delocalization of electron transport layer (ETL) via lithium bis(trifluoromethanesulfonyl)imide doping is developed. The enhanced π-delocalization in ETL benefits sizeable intermolecular π–π overlap, prone to harvesting electrons and thereby improving charge collection range. Doping also improves the conductivity of both ETL and ultrathin silver electrode. Furthermore, the trap densities in ETL and STOPV devices are reduced after doping, contributing to suppressed recombination and higher PCE. Consequently, ETL doping maintains an average visible transmittance of ~ 30% while promotes the PCE of STOPVs from 13.0% to 14.3% and light utilization efficiency from 3.74% to 4.15%, which is among the highest values of optical structure-free STOPVs. This work provides a new insight of π-delocalization manipulation in ETL for efficient STOPVs.

The online version contains supplementary material available at 10.1007/s40820-026-02083-1.