The presence of hot carriers is presented in the operational properties of an (FA,Cs)Pb(I, Br, Cl... more The presence of hot carriers is presented in the operational properties of an (FA,Cs)Pb(I, Br, Cl)3 solar cell at ambient temperatures and under practical solar concentration. At 100 K, clear evidence of hot carriers is observed in both the high energy tail of the photoluminescence spectra and from the appearance of a non-equilibrium photocurrent at higher fluence in light J-V measurements. At room temperature, however, the presence of hot carriers in the emission at elevated laser fluence are shown to compete with a gradual red shift in the PL peak energy as photo induced halide segregation begins to occur at higher lattice temperature. The effects of thermionic emission of hot carriers and the presence of a non-equilibrium carrier distribution are also shown to be distinct from simple lattice heating. This results in large unsaturated photocurrents at high powers as the Fermi distribution exceeds that of the heterointerface controlling carrier transport and rectification.
Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to stud... more Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to study the affect of changing the different components of a perovskite compound, be it A, B, or X. Four different films are compared: FAMAPbSnI 3 , FAPbI 3 , FAMAPbI 3 , and FAPbBr 3. The low temperature results highlight the changes that occur especially, underlying ones that are easily masked at room temperature. The overall Stokes shift is of similar magnitude at room temperature for the three Pb only based samples. This is governed by the interaction strength Γ LO , phonon energy E LO , and the exciton binding energy E ex. One exception to this behavior is the Sn-based FAMAPbSnI 3 film which shows a lack of Stokes shift between the absorption and photoluminescence. However, the strong absorption (more than 100 meV) below the band gap is indicative of an excitonic feature that has a large density of states. Transient absorption measurements confirm the trends observed in continuous wave (CW) measurements, the three Pb only films all show the convolution of an excitonic feature within 20 meV of the band gap as a contributing factor to the photobleach along with a region of high energy PIA. However, the behavior for the Sn-based film is notably different (just as it is in the CW measurements) with an unusual low energy PIA and a lack of high energy PIA. The large unusual low energy PIA is attributed to the large sub band gap absorption observed in the CW transmission/absorption measurements. Notably regardless of interchanging components, the slow cooling of carriers in metal-halide perovsites shows little effect of Γ LO , E LO , and E ex. As such, here it is proposed-while the initial cooling of carriers is attributed to LO phonons, the overall cooling of carriers is dominated by the intrinsic low thermal conductivity of all metal-halide perovskites which limits the dissipation of acoustic phonons in these systems.
Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to stud... more Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to study the affect of changing the different components of a perovskite compound, be it A, B, or X. Four different films are compared: FAMAPbSnI 3 , FAPbI 3 , FAMAPbI 3 , and FAPbBr 3. The low temperature results highlight the changes that occur especially, underlying ones that are easily masked at room temperature. The overall Stokes shift is of similar magnitude at room temperature for the three Pb only based samples. This is governed by the interaction strength Γ LO , phonon energy E LO , and the exciton binding energy E ex. One exception to this behavior is the Sn-based FAMAPbSnI 3 film which shows a lack of Stokes shift between the absorption and photoluminescence. However, the strong absorption (more than 100 meV) below the band gap is indicative of an excitonic feature that has a large density of states. Transient absorption measurements confirm the trends observed in continuous wave (CW) measurements, the three Pb only films all show the convolution of an excitonic feature within 20 meV of the band gap as a contributing factor to the photobleach along with a region of high energy PIA. However, the behavior for the Sn-based film is notably different (just as it is in the CW measurements) with an unusual low energy PIA and a lack of high energy PIA. The large unusual low energy PIA is attributed to the large sub band gap absorption observed in the CW transmission/absorption measurements. Notably regardless of interchanging components, the slow cooling of carriers in metal-halide perovsites shows little effect of Γ LO , E LO , and E ex. As such, here it is proposed-while the initial cooling of carriers is attributed to LO phonons, the overall cooling of carriers is dominated by the intrinsic low thermal conductivity of all metal-halide perovskites which limits the dissipation of acoustic phonons in these systems.
The high tolerance and stability of triple halide perovskite solar cells is demonstrated in pract... more The high tolerance and stability of triple halide perovskite solar cells is demonstrated in practical space conditions at high irradiation levels. The solar cells were irradiated for a range of proton energies (75 keV, 300 keV, and 1 MeV) and fluences (up to 4 × 1014 p/cm2). The fluences of the energy proton irradiations were varied to induce the same amount of vacancies in the absorber layer due to non-ionizing nuclear energy loss (predominant at <300 keV) and electron ionization loss (predominant at >300 keV). While proton irradiation of the solar cells initially resulted in degradation of the photovoltaic parameters, self-healing was observed after two months where the performance of the devices was shown to return to their pristine operation levels. Their ability to recover upon radiation exposure supports the practical potential of perovskite solar cells for next-generation space missions.
Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to stud... more Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to study the affect of changing the different components of a perovskite compound, be it A, B, or X. Four different films are compared: FAMAPbSnI 3 , FAPbI 3 , FAMAPbI 3 , and FAPbBr 3. The low temperature results highlight the changes that occur especially, underlying ones that are easily masked at room temperature. The overall Stokes shift is of similar magnitude at room temperature for the three Pb only based samples. This is governed by the interaction strength Γ LO , phonon energy E LO , and the exciton binding energy E ex. One exception to this behavior is the Sn-based FAMAPbSnI 3 film which shows a lack of Stokes shift between the absorption and photoluminescence. However, the strong absorption (more than 100 meV) below the band gap is indicative of an excitonic feature that has a large density of states. Transient absorption measurements confirm the trends observed in continuous wave (CW) measurements, the three Pb only films all show the convolution of an excitonic feature within 20 meV of the band gap as a contributing factor to the photobleach along with a region of high energy PIA. However, the behavior for the Sn-based film is notably different (just as it is in the CW measurements) with an unusual low energy PIA and a lack of high energy PIA. The large unusual low energy PIA is attributed to the large sub band gap absorption observed in the CW transmission/absorption measurements. Notably regardless of interchanging components, the slow cooling of carriers in metal-halide perovsites shows little effect of Γ LO , E LO , and E ex. As such, here it is proposed-while the initial cooling of carriers is attributed to LO phonons, the overall cooling of carriers is dominated by the intrinsic low thermal conductivity of all metal-halide perovskites which limits the dissipation of acoustic phonons in these systems.
Abstract Mixed organic-inorganic halide perovskite solar cells (PSCs) have received considerable ... more Abstract Mixed organic-inorganic halide perovskite solar cells (PSCs) have received considerable attention in recent years for their impressive solar to electrical power efficiency gains and potentially lower material and processing costs for optoelectronic applications. In addition to terrestrial applications, PSCs are of interest to the space power markets for their low cost, low weight, adaptability to flexible architectures, and tolerance to high energy particle irradiation (mainly protons and electrons). Here we investigate the properties of mixed formamidinium-methylammonium tin-lead iodide (FASn)0.6(MAPb)0.4I3 perovskites which lower the lead content as well as the bandgap, making them attractive for the low bandgap absorber material in tandem PSCs. Through current density-voltage (JV) characterization at lower temperatures, majority carrier transport is hindered and a barrier to photogenerated carrier extraction is evident. This is attributed to the thermally induced change of the bandgap of the absorber layer relative to the energy selective contacts in the device. We find that although the architecture used here hinders the performance at temperatures below 225 K, the tolerance to high energy (3.7 MeV) protons is impressive, considerably out-performing commercially available thin-film CIGS. These results suggest further improvements to structural and interface stability as well as lightweight encapsulation could lead to all perovskite flexible tandem arrays deployed for power generation on missions to low Earth orbit, the moon, Mars, and beyond.
Two different single junction mixed organic-inorganic halide perovskite solar cells (PSCs) were a... more Two different single junction mixed organic-inorganic halide perovskite solar cells (PSCs) were assessed for their tolerance to high energy proton radiation. Both the narrow band gap mixed tin-lead iodide and wide band gap lead iodide-bromide show remarkable tolerance for fluences up to 1x1011 p/cm2. Both materials show a retention of open circuit voltage and decrease in dark current densities indicating minimal effect on SRH recombination that typically plagues traditional III-V based solar cells. Additionally, a control device that was processed without the perovskite absorber layer showed better diode characteristics and lower dark current densities after proton irradiation. The tolerance of these perovskite as a class of materials is promising for multijunction tandem flexible photovoltaic devices.
The presence of hot carriers is presented in the operational properties of an (FA,Cs)Pb(I, Br, Cl... more The presence of hot carriers is presented in the operational properties of an (FA,Cs)Pb(I, Br, Cl)3 solar cell at ambient temperatures and under practical solar concentration. At 100 K, clear evidence of hot carriers is observed in both the high energy tail of the photoluminescence spectra and from the appearance of a non-equilibrium photocurrent at higher fluence in light J-V measurements. At room temperature, however, the presence of hot carriers in the emission at elevated laser fluence are shown to compete with a gradual red shift in the PL peak energy as photo induced halide segregation begins to occur at higher lattice temperature. The effects of thermionic emission of hot carriers and the presence of a non-equilibrium carrier distribution are also shown to be distinct from simple lattice heating. This results in large unsaturated photocurrents at high powers as the Fermi distribution exceeds that of the heterointerface controlling carrier transport and rectification.
Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to stud... more Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to study the affect of changing the different components of a perovskite compound, be it A, B, or X. Four different films are compared: FAMAPbSnI 3 , FAPbI 3 , FAMAPbI 3 , and FAPbBr 3. The low temperature results highlight the changes that occur especially, underlying ones that are easily masked at room temperature. The overall Stokes shift is of similar magnitude at room temperature for the three Pb only based samples. This is governed by the interaction strength Γ LO , phonon energy E LO , and the exciton binding energy E ex. One exception to this behavior is the Sn-based FAMAPbSnI 3 film which shows a lack of Stokes shift between the absorption and photoluminescence. However, the strong absorption (more than 100 meV) below the band gap is indicative of an excitonic feature that has a large density of states. Transient absorption measurements confirm the trends observed in continuous wave (CW) measurements, the three Pb only films all show the convolution of an excitonic feature within 20 meV of the band gap as a contributing factor to the photobleach along with a region of high energy PIA. However, the behavior for the Sn-based film is notably different (just as it is in the CW measurements) with an unusual low energy PIA and a lack of high energy PIA. The large unusual low energy PIA is attributed to the large sub band gap absorption observed in the CW transmission/absorption measurements. Notably regardless of interchanging components, the slow cooling of carriers in metal-halide perovsites shows little effect of Γ LO , E LO , and E ex. As such, here it is proposed-while the initial cooling of carriers is attributed to LO phonons, the overall cooling of carriers is dominated by the intrinsic low thermal conductivity of all metal-halide perovskites which limits the dissipation of acoustic phonons in these systems.
Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to stud... more Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to study the affect of changing the different components of a perovskite compound, be it A, B, or X. Four different films are compared: FAMAPbSnI 3 , FAPbI 3 , FAMAPbI 3 , and FAPbBr 3. The low temperature results highlight the changes that occur especially, underlying ones that are easily masked at room temperature. The overall Stokes shift is of similar magnitude at room temperature for the three Pb only based samples. This is governed by the interaction strength Γ LO , phonon energy E LO , and the exciton binding energy E ex. One exception to this behavior is the Sn-based FAMAPbSnI 3 film which shows a lack of Stokes shift between the absorption and photoluminescence. However, the strong absorption (more than 100 meV) below the band gap is indicative of an excitonic feature that has a large density of states. Transient absorption measurements confirm the trends observed in continuous wave (CW) measurements, the three Pb only films all show the convolution of an excitonic feature within 20 meV of the band gap as a contributing factor to the photobleach along with a region of high energy PIA. However, the behavior for the Sn-based film is notably different (just as it is in the CW measurements) with an unusual low energy PIA and a lack of high energy PIA. The large unusual low energy PIA is attributed to the large sub band gap absorption observed in the CW transmission/absorption measurements. Notably regardless of interchanging components, the slow cooling of carriers in metal-halide perovsites shows little effect of Γ LO , E LO , and E ex. As such, here it is proposed-while the initial cooling of carriers is attributed to LO phonons, the overall cooling of carriers is dominated by the intrinsic low thermal conductivity of all metal-halide perovskites which limits the dissipation of acoustic phonons in these systems.
The high tolerance and stability of triple halide perovskite solar cells is demonstrated in pract... more The high tolerance and stability of triple halide perovskite solar cells is demonstrated in practical space conditions at high irradiation levels. The solar cells were irradiated for a range of proton energies (75 keV, 300 keV, and 1 MeV) and fluences (up to 4 × 1014 p/cm2). The fluences of the energy proton irradiations were varied to induce the same amount of vacancies in the absorber layer due to non-ionizing nuclear energy loss (predominant at <300 keV) and electron ionization loss (predominant at >300 keV). While proton irradiation of the solar cells initially resulted in degradation of the photovoltaic parameters, self-healing was observed after two months where the performance of the devices was shown to return to their pristine operation levels. Their ability to recover upon radiation exposure supports the practical potential of perovskite solar cells for next-generation space missions.
Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to stud... more Temperature dependent (4 K-300 K) photoluminescence and transmission spectra are analyzed to study the affect of changing the different components of a perovskite compound, be it A, B, or X. Four different films are compared: FAMAPbSnI 3 , FAPbI 3 , FAMAPbI 3 , and FAPbBr 3. The low temperature results highlight the changes that occur especially, underlying ones that are easily masked at room temperature. The overall Stokes shift is of similar magnitude at room temperature for the three Pb only based samples. This is governed by the interaction strength Γ LO , phonon energy E LO , and the exciton binding energy E ex. One exception to this behavior is the Sn-based FAMAPbSnI 3 film which shows a lack of Stokes shift between the absorption and photoluminescence. However, the strong absorption (more than 100 meV) below the band gap is indicative of an excitonic feature that has a large density of states. Transient absorption measurements confirm the trends observed in continuous wave (CW) measurements, the three Pb only films all show the convolution of an excitonic feature within 20 meV of the band gap as a contributing factor to the photobleach along with a region of high energy PIA. However, the behavior for the Sn-based film is notably different (just as it is in the CW measurements) with an unusual low energy PIA and a lack of high energy PIA. The large unusual low energy PIA is attributed to the large sub band gap absorption observed in the CW transmission/absorption measurements. Notably regardless of interchanging components, the slow cooling of carriers in metal-halide perovsites shows little effect of Γ LO , E LO , and E ex. As such, here it is proposed-while the initial cooling of carriers is attributed to LO phonons, the overall cooling of carriers is dominated by the intrinsic low thermal conductivity of all metal-halide perovskites which limits the dissipation of acoustic phonons in these systems.
Abstract Mixed organic-inorganic halide perovskite solar cells (PSCs) have received considerable ... more Abstract Mixed organic-inorganic halide perovskite solar cells (PSCs) have received considerable attention in recent years for their impressive solar to electrical power efficiency gains and potentially lower material and processing costs for optoelectronic applications. In addition to terrestrial applications, PSCs are of interest to the space power markets for their low cost, low weight, adaptability to flexible architectures, and tolerance to high energy particle irradiation (mainly protons and electrons). Here we investigate the properties of mixed formamidinium-methylammonium tin-lead iodide (FASn)0.6(MAPb)0.4I3 perovskites which lower the lead content as well as the bandgap, making them attractive for the low bandgap absorber material in tandem PSCs. Through current density-voltage (JV) characterization at lower temperatures, majority carrier transport is hindered and a barrier to photogenerated carrier extraction is evident. This is attributed to the thermally induced change of the bandgap of the absorber layer relative to the energy selective contacts in the device. We find that although the architecture used here hinders the performance at temperatures below 225 K, the tolerance to high energy (3.7 MeV) protons is impressive, considerably out-performing commercially available thin-film CIGS. These results suggest further improvements to structural and interface stability as well as lightweight encapsulation could lead to all perovskite flexible tandem arrays deployed for power generation on missions to low Earth orbit, the moon, Mars, and beyond.
Two different single junction mixed organic-inorganic halide perovskite solar cells (PSCs) were a... more Two different single junction mixed organic-inorganic halide perovskite solar cells (PSCs) were assessed for their tolerance to high energy proton radiation. Both the narrow band gap mixed tin-lead iodide and wide band gap lead iodide-bromide show remarkable tolerance for fluences up to 1x1011 p/cm2. Both materials show a retention of open circuit voltage and decrease in dark current densities indicating minimal effect on SRH recombination that typically plagues traditional III-V based solar cells. Additionally, a control device that was processed without the perovskite absorber layer showed better diode characteristics and lower dark current densities after proton irradiation. The tolerance of these perovskite as a class of materials is promising for multijunction tandem flexible photovoltaic devices.
Uploads
Papers by Shashi Sourabh