Efficient 1.77 eV-bandgap perovskite and all-perovskite tandem solar cells enabled by long-alkyl phosphonic acid

Abstract

Efficient wide-bandgap (WBG) perovskite solar cells are requisite for constructing superior tandem solar cells. However, their performance has been limited by numerous vacancy defects in the films and suboptimal crystal quality. To tackle this challenge, we propose using a functionalized long-alkyl phosphonic acid molecule, dodecylphosphonic acid (DDPA), as an additive in WBG perovskite precursors. The phosphonic acid group in DDPA molecules interacts with formamidine cations, halogen anions, and undercoordinated Pb²⁺, inhibiting the formation of vacancies, while the long-alkyl groups in DDPA molecules constrain grain tilting during growth. Consequently, the addition of DDPA significantly increases grain sizes, promotes crystal orientation, and reduces vacancy defects, leading to substantially reduced photo-generated carrier recombination in the bulk and at the interface of WBG perovskites. As a result, opaque and semi-transparent 1.77 eV-bandgap solar cells fulfill high power conversion efficiencies of 20.20% and 18.49%, respectively. Furthermore, two-terminal and four-terminal all-perovskite tandem cells deliver remarkable efficiencies of 27.41% (27.20% stabilized) and 28.65% (28.50% stabilized), respectively, revealing significant potential for efficient multijunction solar cell applications.