Top-Down Dual-Interface Carrier Management for Highly Efficient and Stable Perovskite/Silicon Tandem Solar Cells

Abstract

Despite significant advancements in the power conversion efficiency (PCE) of perovskite/silicon tandem solar cells, improving carrier management in top cells remains challenging due to the defective dual interfaces of wide-bandgap perovskite, particularly on textured silicon surfaces. Herein, a series of halide ions (Cl−, Br−, I−) substituted piperazinium salts are designed and synthesized as post-treatment modifiers for perovskite surfaces. Notably, piperazinium chloride induces an asymmetric bidirectional ions distribution from the top to the bottom surface, with large piperazinium cations concentrating at the perovskite surface and small chloride anions migrating downward to accumulate at the buried interface. This results in effective dual-interface defect passivation and energy band modulation, enabling wide-bandgap (1.68 eV) perovskite solar cells to achieve a PCE of 22.3% and a record product of open-circuit voltage × fill factor (84.4% relative to the Shockley–Queisser limit). Furthermore, the device retains 91.3% of its initial efficiency after 1200 h of maximum power point tracking without encapsulation. When integrated with double-textured silicon heterojunction solar cells, a remarkable PCE of 31.5% is achieved for a 1.04 cm2 monolithic perovskite/silicon tandem solar cell, exhibiting excellent long-term operational stability (T80 = 755 h) without encapsulation in ambient air. This work provides a convenient strategy on dual-interface engineering for making high-efficiency and stable perovskite platforms.

1. Introduction

Recently, remarkable advancements have been made in monolithic inverted perovskite/silicon tandem solar cells (PVSK/Si TSCs), with a certified power conversion efficiency (PCE) reaching to 34.6% [1]. By comparing the achieved performance with the theoretical limit of 44.3% [2], as estimated by the Shockley–Queisser (S–Q) theory, it is evident that while the JSC (short-circuit current density)/JSQ (maximum possible current calculated by the S–Q limit) ratio of PVSK/Si TSCs reaches 96%, indicating near-perfect light management, there is still room for improvement in charge carrier management, as the VOC (open-circuit voltage) × FF (fill factor) product typically reaches only around 80% or less of the S–Q limits, significantly lower than the 87% and 85% achieved by perovskite and silicon single-junction solar cells [3–5], respectively.

Previous studies suggested that the defects, in particular at film interfaces of wide-bandgap (WBG) perovskite top cells, could be recognized as the primary source to trigger the VOC × FF losses [6–8]. To date, in PVSK/Si TSCs, most interface engineering efforts have primarily focused on passivating the defective perovskite/C60 top interface [9–12]. However, passivation of the buried interface, which has recently been recognized as equally crucial for device performance of perovskite single-junction solar cells [13–15], has rarely been reported [16–18]. The primary challenge lies in achieving a continuous and conformal passivation layer on the rough pyramid surface of the silicon bottom cell [19], especially for solution-processed interface materials [20, 21], without compromising carrier transport. Additionally, most interface materials are readily dissolved in the highly polar aprotic solvents typically used in perovskite precursor inks, such as N, N-dimethylformamide and dimethylsulfoxide [22], which diminishes the passivation effect and affects the perovskite crystallization process. Therefore, exploring a suitable and feasible method for passivating both interfaces of WBG perovskite on textured silicon surfaces is essential for effective carrier management in PVSK/Si TSCs.

In this work, an innovated top-down dual-interface carrier management strategy is developed to effectively improve both interfaces of the wide-bandgap perovskite using a multi-functionalized piperazinium chloride post-treatment.