Alkali Mono-Pnictides: A New Class of Photovoltaic Materials by Element Mutation

Abstract

Selenium (Se) has been studied for over 140 years as the first solid-state solar cell, yet it has only achieved a maximum power conversion efficiency of 6.5%. To improve the efficiency, we propose derivative structures via element mutation. Specifically, we replace Se with Group 15 pnictogens (Pn = P,As,Sb) and fill the interchain space with alkali metals (M = Li,Na,K,Rb,Cs). Our calculations reveal that the band gaps of MPn span the optimal range for solar absorption. We find that NaP, composed of earth-abundant elements, has excellent properties as a solar cell absorber, including a slightly indirect band gap, high optical absorption coefficient just above the absorption onset, light electron and hole effective masses, and ambipolar dopability. However, carrier capture calculations show that P vacancies may limit its photovoltaic performance. Therefore, we propose solutions to reduce P vacancies through chemical potential control. Finally, we present preliminary results of NaP powder sample growth; this reveals a direct band gap of 1.66 eV, close to the predicted value of 1.62 eV. MPn represents a new class of absorber to rival other emerging photovoltaic technologies.2 MoreReceived 20 May 2023Revised 31 July 2023Accepted 14 August 2023DOI:https://doi.org/10.1103/PRXEnergy.2.043002Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasSolar cellsTechniquesDensity functional calculationsFirst-principles calculationsCondensed Matter, Materials & Applied Physics