Muhammad Akmal Kamarudin

Mixed Sn–Ge Perovskite for Enhanced Perovskite Solar Cell Performance in Air

Lead-based perovskite solar cells have gained ground in recent years, showing efficiency as high as 20%, which is on par with that of silicon solar cells. However, the toxicity of lead makes it a nonideal candidate for use in solar cells. Alternatively, tin-based perovskites have been proposed because of their nontoxic nature and abundance. Unfortunately, these solar cells suffer from low efficiency and stability. Here, we propose a new type of perovskite material based on mixed tin and germanium. The material showed a band gap around 1.4-1.5 eV as measured from photoacoustic spectroscopy, which is ideal from the perspective of solar cells. In a solar cell device with inverted planar structure, pure tin perovskite solar cell showed a moderate efficiency of 3.31%. With 5% doping of germanium into the perovskite, the efficiency improved up to 4.48% (6.90% after 72 h) when measured in air without encapsulation.

Dependence of Acetate-Based Antisolvents for High Humidity Fabrication of CH3NH3PbI3 Perovskite Devices in Ambient Atmosphere

High-efficiency perovskite solar cells (PSCs) need to be fabricated in the nitrogen-filled glovebox by the atmosphere-controlled crystallization process. However, the use of the glovebox process is of great concern for mass level production of PSCs. In this work, notable efficient CH3NH3PbI3 solar cells can be obtained in high humidity ambient atmosphere (60-70% relative humidity) by using acetate as the antisolvent, in which dependence of methyl, ethyl, propyl, and butyl acetate on the crystal growth mechanism is discussed. It is explored that acetate screens the sensitive perovskite intermediate phases from water molecules during perovskite film formation and annealing. It is revealed that relatively high vapor pressure and high water solubility of methyl acetate (MA) leads to the formation of highly dense and pinhole free perovskite films guiding to the best power conversion efficiency (PCE) of 16.3% with a reduced hysteresis. The devices prepared using MA showed remarkable shelf life stability of more than 80% for 360 h in ambient air condition, when compared to the devices fabricated using other antisolvents with low vapor pressure and low water solubility. Moreover, the PCE was still kept at 15.6% even though 2 vol % deionized water was added in the MA for preparing the perovskite layer.

Enhanced Crystallization by Methanol Additive in Antisolvent for Achieving High-Quality MAPbI3 Perovskite Films in Humid Atmosphere

Perovskite solar cells have attracted considerable attention owing to their easy and low-cost solution manufacturing process with high power conversion efficiency. However, the fabrication process is usually performed inside a glovebox to avoid moisture, as organometallic halide perovskites are easily dissolved in water. In this study, we propose a one-step fabrication of high-quality MAPbI3 perovskite films in around 50u2009% relative humidity (RH) humid ambient air by using diethyl ether as an antisolvent and methanol as an additive into this antisolvent. Because of the presence of methanol, the water molecules can be efficiently removed from the gaps of the perovskite precursors and the perovskite film formation can be slightly controlled, leading to pinhole-free and low roughness films. Concurrently, methanol can be used to tune the DMSO ratio in the intermediate perovskite phase to regulate perovskite formation. Planar solar cells fabricated by using this method exhibited the best efficiency of 16.4u2009% with a reduced current density-voltage hysteresis. This efficiency value is approximately 160u2009% higher than the devices fabrication by using only diethyl ether treatment. From the impedance measurement, it is also found that the recombination reaction is suppressed when the device is prepared with methanol additive in the antisolvent. This method presents a new path for controlling the growth and morphology of perovskite films in humid climates and laboratories with uncontrolled environments.

All‐Inorganic CsPb1−xGexI2Br Perovskite with Enhanced Phase Stability and Photovoltaic Performance

Compared with organic-inorganic perovskites, all-inorganic cesium-based perovskites without volatile organic compounds have gained extensive interests because of the high thermal stability. However, they have a problem on phase transition from cubic phase (active for photo-electric conversion) to orthorhombic phase (inactive for photo-electric conversion) at room temperature, which has hindered further progress. Herein, novel inorganic CsPb1-x Gex I2 Br perovskites were prepared in humid ambient atmosphere without a glovebox. The phase stability of the all-inorganic perovskite was effectively enhanced after germanium addition. In addition, the highest power conversion efficiency of 10.8u2009% with high open-circuit voltage (VOC ) of 1.27u2005V in a planar solar cell based on CsPb0.8 Ge0.2 I2 Br perovskite was achieved. Furthermore, the highest VOC up to 1.34u2005V was obtained by CsPb0.7 Ge0.3 I2 Br perovskite, which is a remarkable record in the field of all-inorganic perovskite solar cells. More importantly, all the photovoltaic parameters of CsPb0.8 Ge0.2 I2 Br perovskite solar cells showed nearly no decay after 7u2005h measurement in 50-60u2009% relative humidity without encapsulation.

Magnesium-Doped MAPbI3 Perovskite Layers for Enhanced Photovoltaic Performance in Humid Air Atmosphere

Despite the high efficiency of MAPbI3 perovskite solar cells, the long term stability and degradation in humid atmosphere are issues that still needed to be addressed. In this work, magnesium iodide (MgI2) was first successfully used as a dopant into MAPbI3 perovskite prepared in humid air atmosphere. Mg doping decreased the valence band level, which was determined from photoelectron yield spectroscopy. Compared to the pristine MAPbI3 perovskite film, the 1.0% Mg-doped perovskite film showed increased crystal grain size and formation of pinhole-free perovskite film. Performance of the solar cell was increased from 14.2% of the doping-free solar cell to 17.8% of 1.0% Mg-doped device. Moreover, 90% of the original power conversion efficiency was still retained after storage in 30-40% relative humidity for 600 h.

Pb free perovskite solar cells consisting of mixed metal SnGe perovskite as light absorber (Conference Presentation)

Despite the high-efficiency of these lead-based perovskite solar cells, the problem associated from the toxic nature of lead has open a new research direction which focuses on lead-free perovskite materials. As an alternative, tin has been proposed to replace lead. The highest efficiency obtained with Sn only perovskite was 9 % which was based on 2D and 3D mixture of FASnI3. However, Sn-based perovskites are known to have low stability in air. The use of germanium-based perovskite in solar cell was first realized by Krishnamoorthy et. al. The measured solar cell performance was notably low, 0.11 % for CsGeI3 and 0.20 % for MAGeI3. A theoretical study exploring hybrid tin and germanium perovskite showed that it is possible to prepare a stable Sn-Ge perovskite material that absorbs the sunlight spectrum. In this study, a new type of SnGe mixed metal perovskite solar cells are reported with enhanced efficiency and stability. In this report, FA0.75MA0.25Sn1-xGexI3 (abbreviated as SnGe(x)-PVK) were used for the mixed metal SnGe perovskite. XRD spectra showed that the structure is perovskite.nThe structure of Ge-doped Sn perovskite was also discussed from the view point of band gap, conduction and valence band level, XPS analysis, and the urbach energy. It can be concluded that most of the Ge atoms passivate the surface of the Sn perovskite (graded structure).For SnGe(0)-PVK device, the averageJsc was 17.61 mA/cm2, VOC was 0.46 V, FF was 0.41 and PCE of 3.31 %. Upon doping with 5 wt% of Ge, the JSC increased up to 19.80 mA/cm2, FF improved up to 0.55 with an overall efficiency of 4.48 %. Upon increasing the Ge content more than 10wt%, all the photovoltaic parameters decreased significantly which resulted in an efficiency as low as 0.80 % for SnGe(0.2)-PVK device. After optimization, 7.75% of SnGe(5)-PVK device is reported. Significant effect on Ge doping was seen in the enhancement of the stability. The stability in air has been improved significantly with the Ge doping, retaining 80 % of its original performance, remarkable stability enhancement, compared with 10 % retention for non-doped sample. This work provides a platform for further research on lead-free Sn-Ge based perovskite solar cells.

Interfacial sulfur functionalization anchoring SnO2 and CH3NH3PbI3 for enhanced stability and trap passivation in perovskite solar cells

Trap states at the interface or in bulk perovskite materials critically influence perovskite solar cells performance and long-term stability. Here, a strategy for efficiently passivating charge traps and mitigating interfacial recombination by SnO2 surface sulfur functionalization is reported, which utilizes xanthate decomposition on the SnO2 surface at low temperature. The results show that functionalized sulfur atoms can coordinate with under-coordinated Pb2+ ions near the interface. After device fabrication under more than 60u2009% humidity in ambient air, the efficiency of methylammonium lead iodide (MAPbI3 ) perovskite solar cells based on sulfur-functionalized SnO2 increased from 16.56u2009% to 18.41u2009% with suppressed hysteresis, which resulted from the accelerated interfacial charge transport kinetics and decreased traps in bulk perovskite by interfacial sulfur functionalization. Additionally, thermally stimulated current studies show the decreased trap density in the shallow trap area after interfacial sulfur functionalization. The interfacial sulfur functionalized solar cells without sealing also exhibited considerable retardation of solar cell degradation with only 10u2009% degradation after 70 days air storage. This work demonstrates a facile sulfur functionalization strategy by using xanthate decomposition on SnO2 surfaces to obtain highly efficient perovskite solar cells.

Performance Enhancement of Mesoporous TiO2-Based Perovskite Solar Cells by SbI3 Interfacial Modification Layer

TiO2 is commonly used as an electron-transporting material in perovskite photovoltaic devices due to its advantages, including suitable band gap, good photoelectrochemical stability, and simple preparation process. However, there are many oxygen vacancies or defects on the surface of TiO2 and thus this affects the stability of TiO2-based perovskite solar cells under UV light. In this work, a thin (monolayer) SbI3 modification layer is introduced on the mesoporous TiO2 surface and the effect at the interface between of TiO2 and perovskite is monitored by using a quartz crystal microbalance system. We demonstrate that the SbI3-modified TiO2 electrodes exhibit superior electronic properties by reducing electronic trap states, enabling faster electron transport. This approach results in higher performances compared with electrodes without the SbI3 passivation layer. CH3NH3PbI3 perovskite solar cells with a maximum power conversion efficiency of 17.33% in air, accompanied by a reduction in hysteresis and enhancement of the device stability, are reported.