# High-Efficiency Perovskite/Silicon Tandem Solar Cells Based on Wide-Bandgap Perovskite Solar Cells with Unprecedented Fill Factor

## TL;DR

This paper presents a new method to improve perovskite solar cells by creating a better interface, leading to high efficiency and performance.

## Contribution

A blended self-assembled monolayer improves interfacial energy alignment, achieving record fill factor and efficiency in perovskite solar cells.

## Key findings

- A blended SAM of 2PACz and Me-4PACz achieves a certified fill factor of 86.8% and 23.42% efficiency.
- Lower interface defect densities improve fill factor, while higher densities affect open-circuit voltage.
- The method enables a four-terminal tandem solar cell with 30.97% efficiency.

## Abstract

By mixing 2PACz and Me-4PACz, an energetically homogeneous buried interface is formed, enabling preferential energy alignment at the hole transport layer/perovskite (1.67 eV) interface, which delivers a certified fill factor of 86.8% and a power conversion efficiency of 23.42%.Simulations indicate that at lower interface defect densities (1 × 108–1 × 1011 cm−2), improvements in FF dominate the device performance, whereas at higher defect densities (1 × 1012–1 × 1013 cm−2), Voc is the key factor.

By mixing 2PACz and Me-4PACz, an energetically homogeneous buried interface is formed, enabling preferential energy alignment at the hole transport layer/perovskite (1.67 eV) interface, which delivers a certified fill factor of 86.8% and a power conversion efficiency of 23.42%.

Simulations indicate that at lower interface defect densities (1 × 108–1 × 1011 cm−2), improvements in FF dominate the device performance, whereas at higher defect densities (1 × 1012–1 × 1013 cm−2), Voc is the key factor.

The online version contains supplementary material available at 10.1007/s40820-025-01959-y.

Recent progress in inverted perovskite solar cells (iPSCs) highlights the critical role of interface engineering between the charge transport layer and perovskite. Self-assembled monolayers (SAM) on transparent conductive oxide electrodes serve effectively as hole transport layers, though challenges such as energy mismatches and surface inhomogeneities remain. Here, a blended self-assembled monolayer of (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) and (4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACz) is developed, offering improved surface potential uniformity and interfacial energy alignment compared to individual SAMs. Interactions between the SAMs and ionic species are investigated with simulation analysis conducted, revealing the elimination of interfacial energy barriers through precise energy-level tuning. This strategy enables wide-bandgap (1.67 eV) perovskite solar cells with inverted structures with over 24% efficiency, an open-circuit voltage (Voc) of 1.268 V, and a certified fill factor (FF) of 86.8%, leading to a certified efficiency of 23.42%. The approach also enables high-efficiency semi-transparent devices and a mechanically stacked four-terminal perovskite/silicon tandem solar cell reaching 30.97% efficiency.

The online version contains supplementary material available at 10.1007/s40820-025-01959-y.