Xin Zheng1
Huazhong University of Science & Technology1
Xin Zheng1
Huazhong University of Science & Technology1
In recent years, the photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%. However, according to Shockley-Queisser's limitations, the maximum theoretical efficiency of a single-junction solar cell is about 33%. The room for efficiency improvement of single-junction perovskite solar cells is very limited. Therefore, the development of tandem solar cells is an important way to break the limit and further improve the efficiency of PSCs. The theoretical limit efficiency of double-junction tandem solar cells (TSCs) can reach 46%, which is much higher than that of single-junction solar cells. In practice, The efficiency of all-perovskite tandem solar cells (28%) has surpassed that of single-junction perovskite solar cells (26%). Wide-bandgap (WBG) mixed-halide perovskites show promise of realizing efficient tandem solar cells but at present suffer from large open-circuit voltage loss because of excess lead iodide and light-induced halide phase segregation.<br/>Here, a crosslink polymer strategy with high crosslinking degree and high density of functional groups is reported for finely regulating the crystal growth of FA<sub>0.8</sub>Cs<sub>0.2</sub>Pb(I<sub>0.6</sub>Br<sub>0.4</sub>)<sub>3</sub>, thereby obtaining high-performance PSCs. The pentaerythritol tetraacrylate (PTA) is introduced to form hydrogen bonds and strong Pb–O bonds with perovskite precursors, realizing the complete elimination of excess lead iodide. Besides, this uniformly distributed PTA crosslink polymer system passivates the defects and inhibits the photo-induced halide segregation effectively. The prepared PSCs with a band gap of 1.77 eV yield an impressive open-circuit voltage (<i>V</i><sub>OC</sub>) of 1.36 V, corresponding to a record low <i>V</i><sub>OC</sub> -deficit of 0.41 V and an efficiency of 19.58%. With these WBG perovskite subcells, we report 27.3% monolithic all-perovskite TSCs shows an outstanding combination of a high <i>V</i><sub>OC</sub> of 2.15 V and a FF of 81.4% with improved operational stability.