Lead‐Free Hybrid Perovskite Absorbers for Viable Application: Can We Eat the Cake and Have It too?

Abstract

Many years since the booming of research on perovskite solar cells (PSCs), the hybrid perovskite materials developed for photovoltaic application form three main categories since 2009: (i) high‐performance unstable lead‐containing perovskites, (ii) low‐performance lead‐free perovskites, and (iii) moderate performance and stable lead‐containing perovskites. The search for alternative materials to replace lead leads to the second group of perovskite materials. To date, a number of these compounds have been synthesized and applied in photovoltaic devices. Here, lead‐free hybrid light absorbers used in PV devices are focused and their recent developments in related solar cell applications are reviewed comprehensively. In the first part, group 14 metals (Sn and Ge)‐based perovskites are introduced with more emphasis on the optimization of Sn‐based PSCs. Then concerns on halide hybrids of group 15 metals (Bi and Sb) are raised, which are mainly perovskite derivatives. At the same time, transition metal Cu‐based perovskites are also referred. In the end, an outlook is given on the design strategy of lead‐free halide hybrid absorbers for photovoltaic applications. It is believed that this timely review can represent our unique view of the field and shed some light on the direction of development of such promising materials.

A Two‐Step Modified Sequential Deposition Method‐based Pb‐Free (CH3NH3)3Sb2I9 Perovskite with Improved Open Circuit Voltage and Performance

“…prepared a mixed halide Pb based perovskite and the developed perovskite solar cells (PSCs) device exhibited an highest PCE of 19.33 % and highest PCE of 23 % was certified by NREL . However, in general low stability and highly toxic nature of Pb restricted production at large scale for commercialization . Thus, Hou et al .…”

Progress of Lead‐Free Halide Double Perovskites

“…[130] The valence band maximum (VBM) of MAPbI 3 is therefore made up of a mixture of the filled 6s 2 and 5p 6 states of Pb 2+ and I − , while the conduction band minimum (CBM) is made up of the vacant 6p state of Pb 2+ . Despite the similarities in the electronic configuration of Pb 2+ and Bi 3+ , literature survey [25,62,81,133,134] shows that Cs 2 AgBiBr 6 and other members of this class of compounds exhibit inferior photophysical properties to those of MAPbI 3 . However, only Bi 3+ is known to be nontoxic and has been used in organic reactions as a nontoxic additive.…”

“…The enlarged bandgap can be ascribed to the quantum confinement effect in Cs 2 AgBiBr 6 NCs. [133,134] The discrepancies can be attributed to the differences of preparation methods, [62,76] characterization techniques, [25,62,141] and structural models used in calculations. [139] This peak is blue shifted (more than 1 eV) from the band edge.…”

“…This leads to a localized, narrow conduction band and a wide bandgap. [133,134,193] To date, halide double perovskites have displayed inferior material and device performance compared to the Pb based perovskites. The preparation of the compounds also often requires high temperature.…”

Improving Performance of Lead‐Free Formamidinium Tin Triiodide Perovskite Solar Cells by Tin Source Purification

“…Previous work has demonstrated that Sn, germanium (Ge), bismuth (Bi), and antimony (Sb) are possible elements to replace Pb, and recently the strategy of cation‐transmutation to design double‐perovskites (A 2 M + M 3+ X 6 ) reveals a new way to replace Pb, among which the most promising choice is Sn according to the efficiencies ever reported. As an element sits just above Pb in group 14 of the periodic table, Sn‐based perovskites adopt similar structure to those of Pb‐based counterparts, which leads to analogical photovoltaic characteristics, such as high absorption coefficient, small exciton binding energy and high carrier mobility, etc .…”