W(Nb)Ox-based efficient flexible perovskite solar cells: From material optimization to working principle

Abstract

Flexible perovskite solar cell (PSC) using plastic substrate is one of the most focal points in the studies of thin-film solar cells. Low-temperature preparation of suitable electron selective layer (ESL) is the key issue in the fabrication of flexible PSCs. In this work, amorphous niobium-modified tungsten oxide W(Nb)Ox was prepared as ESL for efficient flexible PSC. Modification using Nb5+ improved the electron transport of WOx-based ESL by enhancing donor density, reducing interfacial depletion width, and minimizing trap states in the ESL. Consequently, photovoltaic performance of the simple planar flexible PSCs was improved, and high PCEs of 15.65% and 13.14% were obtained when ESLs were fabricated at 120°C and room temperature, respectively. In addition, the effect of ESL thickness on the hysteresis behavior of PSCs was carefully analyzed. A capacitance CE across the ESL in the ITO/ESL/perovskite structure was proposed. This capacitance could well indicate the effect of ESL thickness on hysteresis behavior. The proposed modification strategy and mechanism is expected to facilitate the development of novel and advanced functional materials.