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The optoelectronic role of chlorine in CH3NH3PbI3(Cl)-based perovskite solar cells.

Chen Q, Zhou H, Fang Y, Stieg AZ, Song TB, Wang HH, Xu X, Liu Y, Lu S, You J, Sun P, McKay J, Goorsky MS, Yang Y - Nat Commun (2015)

Bottom Line: Specifically, chlorine incorporation has been shown to affect the morphological development of perovksite films, which results in improved optoelectronic characteristics for high efficiency.Here we report an effective strategy to investigate the role of the extrinsic ion in the context of optoelectronic properties, in which the morphological factors that closely correlate to device performance are mostly decoupled.The chlorine incorporation is found to mainly improve the carrier transport across the heterojunction interfaces, rather than within the perovskite crystals.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, USA [2] California NanoSystems Institute, University of California, Los Angeles, California 90095, USA.

ABSTRACT
Perovskite photovoltaics offer a compelling combination of extremely low-cost, ease of processing and high device performance. The optoelectronic properties of the prototypical CH3NH3PbI3 can be further adjusted by introducing other extrinsic ions. Specifically, chlorine incorporation has been shown to affect the morphological development of perovksite films, which results in improved optoelectronic characteristics for high efficiency. However, it requires a deep understanding to the role of extrinsic halide, especially in the absence of unpredictable morphological influence during film growth. Here we report an effective strategy to investigate the role of the extrinsic ion in the context of optoelectronic properties, in which the morphological factors that closely correlate to device performance are mostly decoupled. The chlorine incorporation is found to mainly improve the carrier transport across the heterojunction interfaces, rather than within the perovskite crystals. Further optimization according this protocol leads to solar cells achieving power conversion efficiency of 17.91%.

No MeSH data available.


Related in: MedlinePlus

Carrier behaviour of the perovskite film.TRPL measurements and the fitting curves for Reference (a) and Sample 1 (b) in the presence of quenchers (Spiro-OMeTAD or PCBM, respectively). TRPL measurements taken at the peak emission wavelength are recorded (black square) with an electron transport layer (PCBM; blue triangles) or a hole transport layer (Spiro-OMeTAD; red circles), along with stretched exponential fits in corresponding colours. TRPL spectra were obtained using the time-correlated single-photon counting technique (Picoharp 300) under excitation provided by a picosecond diode laser at a wavelength of 633 nm with a repetition frequency of 1 MHz (PDL 800B).
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f5: Carrier behaviour of the perovskite film.TRPL measurements and the fitting curves for Reference (a) and Sample 1 (b) in the presence of quenchers (Spiro-OMeTAD or PCBM, respectively). TRPL measurements taken at the peak emission wavelength are recorded (black square) with an electron transport layer (PCBM; blue triangles) or a hole transport layer (Spiro-OMeTAD; red circles), along with stretched exponential fits in corresponding colours. TRPL spectra were obtained using the time-correlated single-photon counting technique (Picoharp 300) under excitation provided by a picosecond diode laser at a wavelength of 633 nm with a repetition frequency of 1 MHz (PDL 800B).

Mentions: To gain insight into the effects of Cl incorporation, the carrier transport properties of the Reference and Sample 1 are carefully examined, either within the absorber layer or across the heterojunction. The carrier dynamics in the perovskite heterojunction is reported to follow the relation (1/τHeterojunction=1/τCT+1/τPerovskite), where the two major competing process regarding charge transport are carrier recombination (τPerovskite) and charge-carrier transfer (τCT)39. TRPL measurements are thus employed to extract the carrier lifetime in the perovskite films (τPerovskite), which has been successfully applied to describe various radiative and non-radiative loss channels responsible for photoexcited carriers recombination38. The samples for this measurement were fabricated on glass substrates in the same condition when the optimized devices were produced. (See Supplementary Information). Figure 5 shows the photoluminescence decay profiles of Sample 1 and Reference with/without quenching layers. Sample 1 (with chlorine inclusion) shows a τ value of 241 ns, which is in good agreement to that of CH3NH3PbI3−xClx films by one-step deposition in the absence of quenching layers38. Interestingly, a τ value of 289 ns was measured for Reference (CH3NH3PbI3) without quenching layer, which was over one order of magnitude higher than that of CH3NH3PbI3 fabricated via conventional one-step deposition as previously reported3839. The addition of the PCBM or Spiro-OMeTAD quenching layers accelerates the PL decay for both Reference and Sample 1. The observed time constants for PCBM-quenched Reference and Sample 1 are ∼11.8 and 9.6 ns, respectively, and those for Spiro-OMeTAD quenched ones are 9.6 and 5.6 ns, respectively. Taking into account the comparable carrier diffusion coefficient as previously reported38, the corresponding diffusion length for electrons and holes were estimated to well exceed the thickness of the absorber layer for both Reference and Sample 1. These results serve as additional evidence to explain the superior performance of devices in CH3NH3PbI3-based planar configuration documented recently414243. It also suggests that carrier dynamics in perovksite films closely correlates to processing conditions. The exceptionally long carrier lifetime of the Reference agrees with the improved film morphology in terms of both film conformity and grain size while providing an ideal starting point to further unravel material interaction at the interfaces induced by incorporation of extrinsic ions. As the characteristic charge-carrier transfer lifetime τCT is <1 ns (ref. 39), it is reasonable to conclude that 1/τCT is predominant to determine the carrier dynamics across the heterojunction. It implies that carrier lifetimes (τPerovskite) with this same magnitude of several hundred ns do not contribute significant variation to the device performance. The comparable carrier lifetimes in both samples indicate that the chlorine incorporation does not affect the non-radiative recombination channels in the perovskite films.


The optoelectronic role of chlorine in CH3NH3PbI3(Cl)-based perovskite solar cells.

Chen Q, Zhou H, Fang Y, Stieg AZ, Song TB, Wang HH, Xu X, Liu Y, Lu S, You J, Sun P, McKay J, Goorsky MS, Yang Y - Nat Commun (2015)

Carrier behaviour of the perovskite film.TRPL measurements and the fitting curves for Reference (a) and Sample 1 (b) in the presence of quenchers (Spiro-OMeTAD or PCBM, respectively). TRPL measurements taken at the peak emission wavelength are recorded (black square) with an electron transport layer (PCBM; blue triangles) or a hole transport layer (Spiro-OMeTAD; red circles), along with stretched exponential fits in corresponding colours. TRPL spectra were obtained using the time-correlated single-photon counting technique (Picoharp 300) under excitation provided by a picosecond diode laser at a wavelength of 633 nm with a repetition frequency of 1 MHz (PDL 800B).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490385&req=5

f5: Carrier behaviour of the perovskite film.TRPL measurements and the fitting curves for Reference (a) and Sample 1 (b) in the presence of quenchers (Spiro-OMeTAD or PCBM, respectively). TRPL measurements taken at the peak emission wavelength are recorded (black square) with an electron transport layer (PCBM; blue triangles) or a hole transport layer (Spiro-OMeTAD; red circles), along with stretched exponential fits in corresponding colours. TRPL spectra were obtained using the time-correlated single-photon counting technique (Picoharp 300) under excitation provided by a picosecond diode laser at a wavelength of 633 nm with a repetition frequency of 1 MHz (PDL 800B).
Mentions: To gain insight into the effects of Cl incorporation, the carrier transport properties of the Reference and Sample 1 are carefully examined, either within the absorber layer or across the heterojunction. The carrier dynamics in the perovskite heterojunction is reported to follow the relation (1/τHeterojunction=1/τCT+1/τPerovskite), where the two major competing process regarding charge transport are carrier recombination (τPerovskite) and charge-carrier transfer (τCT)39. TRPL measurements are thus employed to extract the carrier lifetime in the perovskite films (τPerovskite), which has been successfully applied to describe various radiative and non-radiative loss channels responsible for photoexcited carriers recombination38. The samples for this measurement were fabricated on glass substrates in the same condition when the optimized devices were produced. (See Supplementary Information). Figure 5 shows the photoluminescence decay profiles of Sample 1 and Reference with/without quenching layers. Sample 1 (with chlorine inclusion) shows a τ value of 241 ns, which is in good agreement to that of CH3NH3PbI3−xClx films by one-step deposition in the absence of quenching layers38. Interestingly, a τ value of 289 ns was measured for Reference (CH3NH3PbI3) without quenching layer, which was over one order of magnitude higher than that of CH3NH3PbI3 fabricated via conventional one-step deposition as previously reported3839. The addition of the PCBM or Spiro-OMeTAD quenching layers accelerates the PL decay for both Reference and Sample 1. The observed time constants for PCBM-quenched Reference and Sample 1 are ∼11.8 and 9.6 ns, respectively, and those for Spiro-OMeTAD quenched ones are 9.6 and 5.6 ns, respectively. Taking into account the comparable carrier diffusion coefficient as previously reported38, the corresponding diffusion length for electrons and holes were estimated to well exceed the thickness of the absorber layer for both Reference and Sample 1. These results serve as additional evidence to explain the superior performance of devices in CH3NH3PbI3-based planar configuration documented recently414243. It also suggests that carrier dynamics in perovksite films closely correlates to processing conditions. The exceptionally long carrier lifetime of the Reference agrees with the improved film morphology in terms of both film conformity and grain size while providing an ideal starting point to further unravel material interaction at the interfaces induced by incorporation of extrinsic ions. As the characteristic charge-carrier transfer lifetime τCT is <1 ns (ref. 39), it is reasonable to conclude that 1/τCT is predominant to determine the carrier dynamics across the heterojunction. It implies that carrier lifetimes (τPerovskite) with this same magnitude of several hundred ns do not contribute significant variation to the device performance. The comparable carrier lifetimes in both samples indicate that the chlorine incorporation does not affect the non-radiative recombination channels in the perovskite films.

Bottom Line: Specifically, chlorine incorporation has been shown to affect the morphological development of perovksite films, which results in improved optoelectronic characteristics for high efficiency.Here we report an effective strategy to investigate the role of the extrinsic ion in the context of optoelectronic properties, in which the morphological factors that closely correlate to device performance are mostly decoupled.The chlorine incorporation is found to mainly improve the carrier transport across the heterojunction interfaces, rather than within the perovskite crystals.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, USA [2] California NanoSystems Institute, University of California, Los Angeles, California 90095, USA.

ABSTRACT
Perovskite photovoltaics offer a compelling combination of extremely low-cost, ease of processing and high device performance. The optoelectronic properties of the prototypical CH3NH3PbI3 can be further adjusted by introducing other extrinsic ions. Specifically, chlorine incorporation has been shown to affect the morphological development of perovksite films, which results in improved optoelectronic characteristics for high efficiency. However, it requires a deep understanding to the role of extrinsic halide, especially in the absence of unpredictable morphological influence during film growth. Here we report an effective strategy to investigate the role of the extrinsic ion in the context of optoelectronic properties, in which the morphological factors that closely correlate to device performance are mostly decoupled. The chlorine incorporation is found to mainly improve the carrier transport across the heterojunction interfaces, rather than within the perovskite crystals. Further optimization according this protocol leads to solar cells achieving power conversion efficiency of 17.91%.

No MeSH data available.


Related in: MedlinePlus