The Relation of Phase‐Transition Effects and Thermal Stability of Planar Perovskite Solar Cells

Abstract

A power conversion efficiency of over 20% has been achieved in CH3NH3PbI3‐based perovskite solar cells (PSC), however, low thermal stability associated with the presence of a phase transition between tetragonal and cubic structures near room temperature is a major issue that must be overcome for future practical applications. Here, the influence of the phase transition on the thermal stability of PSCs is investigated in detail by comparing four kinds of perovskite films with different compositions of halogen atoms and organic components. Thermally stimulated current measurements reveal that a large number of carrier traps are generated in solar cells with the perovskite CH3NH3PbI3 as a light absorber after operation at 85 °C, which is higher than the phase‐transition temperature. Electrochemical impedance spectroscopy measurements further exclude effects of a possible morphology change on the formation of carrier traps. These carrier traps are detrimental to the thermal stability. The thermogravimetric analysis does not show a decomposition for any of the materials in the temperature range relevant for operation. The perovskite alloys do not have this phase transition, resulting in effectively suppressed formation of carrier traps. PSCs with improved thermal stability under the standard thermal cycling test are demonstrated.

Influence of Grain Size on Phase Transitions in Halide Perovskite Films

“…[18][19][20][21][22][23] The workhorse system studied to date, methylammonium lead iodide (MAPbI 3 ), is in a tetragonal phase (TP) at room temperature, but undergoes a transition to a cubic phase at high temperature (≈330 K) and an orthorhombic phase (OP) at low temperature (≈150 K). [24] These results provide hints that the thermal stability [27] and phase transition can be influenced by the local environment of the film due to interactions between the material and substrate as well as within the bulk film itself. This hysteresis could be reduced by scraping the film from the substrate and instead measuring randomly oriented powder samples.…”

“…This hysteresis could be reduced by scraping the film from the substrate and instead measuring randomly oriented powder samples. [24] These results provide hints that the thermal stability [27] and phase transition can be influenced by the local environment of the film due to interactions between the material and substrate as well as within the bulk film itself. Unless understood and mitigated, such hysteretic changes at low temperature may limit the use of perovskite solar cells in some specific applications, for example, aerospace applications, which require operation at extremely low temperatures [28] (<200 K).State-of-the-art perovskite films are polycrystalline, which leads to microscale inhomogeneities in a number of properties such as morphology and defect distributions [29][30][31][32] and, in turn, to local variations in the electronic environment for charge carriers.…”

In Situ Formed Gradient Bandgap‐Tunable Perovskite for Ultrahigh‐Speed Color/Spectrum‐Sensitive Photodetectors via Electron‐Donor Control

“…To realize color‐sensitive photodetector as well as spectrum analysis, gradient perovskite film with continuously tunable bandgap was gained by dealing the base K 0.05 MA 0.95 PbCl 2 Br film on a heater with temperature gradient as the perovskites with different halogen ratios will be formed under different temperature,35–37 which will exhibit various photoabsorption spectra. As shown in Figure a, a temperature bridge together with a hot plate and a cold plate were designed for providing gradient temperature.…”

Perovskite Solar Fibers: Current Status, Issues and Challenges

“…Degradation in these solar cells is mainly triggered by environmental factors such as humidity, temperature, air and UV radiation. According to literature and with reference to the most studied and basic semiconductor perovskite, CH 3 NH 3 PbI 3 , it starts to decompose at 55% relative humidity, and this is observed by a notable color change from dark brown to yellow [145][146][147][148][149][150][151]. Generally, the degradation and formation of methyl ammonium lead halide perovskites can be clearly explained using the chemical equation (R e ) below,…”