{"id":"9a084689-9bf4-4a16-bc3e-4306abceac50","arxiv_id":"2411.13745","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Bias and illumination side change how long hot carriers stay hot in working triple-halide perovskite solar cells.","lead":"Hot carriers in perovskite solar cells cool down at different speeds depending on how much current the cell is producing and which side the light enters. This study uses ultrafast laser pulses on complete working devices to measure that effect.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The bias- and geometry-dependent cooling times hinge on the Maxwell-Boltzmann tail fit; the paper's own 'qualitative' caveat and the known PIA contamination make that assumption the key unsecured link.","rationale":"The reader's weakest-assumption identification matches the main risk I see. The abstract's headline claims are quantitative statements about cooling times, not just qualitative statements, and every one of those statements is a fitted parameter derived from Tc(t). If the tail-fitting assumption fails, the specific numbers in Figure 5 and their bias ordering are not physically meaningful. The manuscript's own text reinforces this: it calls the tail fitting 'simple' and says it provides only a 'qualitative assessment,' and it acknowledges PIA in the spectral region used for fitting. The presence of C60 absorption under back-side illumination and the possibility of band-gap renormalization add further reasons why the high-energy tail may not be a clean hot-carrier occupation measure. I do not see this as grounds to reject the paper: the trends may well survive a more rigorous analysis, and the authors are appropriately cautious in places. But the central claim is conditional on a validity check that has not been shown. The reader's verdict of CONDITIONAL is therefore the right call, and my stress test does not move it. The concrete test I propose is a focused re-analysis of the same data rather than new measurements, so it is feasible and would settle the concern directly.","tokens_in":12839,"tokens_out":4199,"duration_ms":42188,"concrete_test":"Re-analyze the raw TA spectra for the 20 W/cm2 front-side condition at Voc, VJsc, and Vmax with two independent checks: (i) fit the high-energy tail over at least two distinct energy windows above the bleach edge and compare the extracted Tc(t); (ii) subtract the above-gap PIA contribution, estimated from a low-fluence or reference TA spectrum, before tail fitting. If the ordering of τ1/τ2 across biases and the front/back difference survive both checks, the central claim is robust; if the ordering changes or Tc becomes window-dependent, the cooling times are not quantitatively reliable.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claims—shorter τ1/τ2 at VJsc and Vmax than at Voc, and faster cooling for front-side than back-side illumination—are obtained by fitting biexponential decays to carrier temperatures extracted from the high-energy tail of ΔA via Eq. (2) (or Eq. (1)). That extraction is valid only if the TA signal in the fitted window is a linear measure of the hot-carrier occupation of a single quasi-equilibrated population with a well-defined quasi-Fermi level. The paper explicitly labels this 'simple tail fitting' used for a 'qualitative assessment' (Results, around Fig. 3(a)), and it also notes that the above-band-gap side of the bleach contains photo-induced absorption (PIA) attributed to refractive-index changes. If the fitted tail includes PIA or other state-filling artifacts, the slope of ln(ΔT/T) versus energy is no longer 1/kBTc, so the extracted Tc(t) curves—and therefore the ordering of cooling times in Fig. 5—lose their physical meaning. Because the bias-dependent trends are the main result and are presented without residuals, error bars, or an independent validation of the tail hypothesis, this is the load-bearing assumption.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports transient absorption measurements on operational triple-halide perovskite solar cells at biases corresponding to VJsc, Vmax, and Voc, for both front- and back-side illumination. Carrier temperatures are extracted from the high-energy tail of the TA spectra using a Maxwell-Boltzmann tail fit (Eq. 2), and the time dependence of Tc is fit with multi-exponential decays to obtain fast (τ1) and slow (τ2) cooling times. The main claims are that cooling times are shorter when current is extracted (VJsc and Vmax) than at open circuit, and that front-side illumination yields faster cooling than back-side illumination; these trends are attributed to the interplay of carrier density, phonon bottleneck, transport, and extraction.","tokens_in":13124,"tokens_out":4190,"duration_ms":38320,"significance":"The work addresses a relevant question—hot-carrier dynamics under realistic operating bias—and provides rare full-device data with both illumination geometries, along with transfer-matrix calculations that support the interpretation of differential absorption. The tail-fitting method is an external standard in the hot-carrier community, and the bias-dependent dataset is potentially valuable. However, the quantitative headline ordering of cooling times is not yet supported with statistical rigor, and the paper's own 'qualitative' caveat plus the known PIA contamination leave the central metric only weakly secured.","major_comments":[{"comment":"The central bias- and geometry-dependent cooling times are extracted from multi-exponential fits whose order is chosen post hoc: the S3 caption explicitly permits tri- or tetra-exponential fits when a biexponential is not possible, and no residuals, fit ranges, or confidence intervals are shown for τ1 and τ2 in Figure 5. Because τ1 spans 3–5 ps and τ2 spans 10–120 ps across conditions, the apparent ordering (shorter cooling with current extraction, faster cooling for front-side illumination) cannot be distinguished from fit ambiguity. The authors should provide fit statistics, uncertainties, and a fixed fitting protocol, or restrict the claims to qualitative trends.","section":"Results, Figure 5 and S3 caption"},{"comment":"The extraction of Tc relies on the assumption that the high-energy tail of ΔT/T is a linear measure of the hot-carrier occupation with a single quasi-Fermi level, yet the paper calls this 'simple tail fitting' giving a 'qualitative assessment' and notes the presence of above-band-gap PIA attributed to refractive-index changes in the same spectral region. If the fitted window contains PIA, the slope is not 1/kBTc and the reported Tc(t) curves lose quantitative meaning. Please add a sensitivity analysis of the fit window, exclude or model the PIA contribution, or explicitly downgrade the quantitative cooling-time claims.","section":"Results, Eq. (2) and Fig. 3(a)"},{"comment":"The text states that only the fast component τ1 relates to hot-carrier dynamics, while τ2 may reflect lattice heating and the low thermal conductivity of the perovskite, yet τ2 is presented in Figure 5 as a cooling time and is included in the bias-dependent comparison. The paper should clarify whether the claim 'carrier thermalization is modulated by carrier extraction' refers to τ1 alone; if so, the τ2 comparisons should be presented as a separate, non-hot-carrier observation rather than as part of the central cooling-time result.","section":"Results, Figure 5(b),(d)"}],"minor_comments":[{"comment":"Equation (1) appears to have a sign error: writing -ΔA(ℏω) = -A0(ℏω) exp(...) implies ΔA = A0 exp(...), which is inconsistent with the text's convention that the high-energy tail of the bleach decays with increasing energy; this should be corrected.","section":"Eq. (1)"},{"comment":"The data availability statement contains the placeholder 'xmlui.XMLWorkflow.default.def-editstep.claimaction' rather than a working repository link; please provide the actual SHAREOK URL.","section":"Data Availability"},{"comment":"Reference 49 is an MRS meeting abstract with incomplete author information; if it is the only support for the 'non-equivalent carrier dynamics' of HTL/perovskite and ETL/perovskite substacks, please cite the published version or provide full details.","section":"References"},{"comment":"The figure caption does not specify whether the J-V curves are measured under 1-sun AM1.5G in the same operating configuration as the TA bias points; please state whether forward/reverse scans and the indicated voltages refer to this specific device.","section":"Figure 1(c) caption"}],"recommendation":"major_revision","confidential_remarks":"The manuscript fits the journal's scope and the dataset is potentially valuable, but the headline quantitative claims need stronger fit statistics and a more careful framing of the tail-fitting limitation. No concerns about novelty or attribution; the main risk is overinterpretation of noisy multi-exponential fits."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The one thing you should know: this is a genuine step beyond film-level hot-carrier studies—power-dependent, bias-resolved TA on a complete triple-halide perovskite cell, with front and back illumination. The bias-dependence of cooling times (shorter at VJsc and Vmax than at Voc, and faster for front-side than back-side excitation) is new and, if confirmed, useful for hot-carrier device design. The device is high quality (negligible J-V hysteresis), and the transfer-matrix simulations in the SI give a credible explanation for the front/back absorption difference. The authors are also honest: they call the tail fitting a 'qualitative assessment' and note that only the fast decay component relates to hot-carrier dynamics. That transparency counts for something.\n\nThe soft spots are real, though. The central extraction—Tc from the Maxwell-Boltzmann tail—is the load-bearing assumption. The paper itself flags PIA above the band gap from refractive-index changes. If the fitted tail includes that PIA, the slope is no longer simply 1/kBTc, and the ordering of tau1 and tau2 could shift. There are no error bars, no residuals, and the fit order is allowed to be bi-, tri-, or even tetra-exponential. That is a lot of flexibility, and it weakens the quantitative claims. There's also an internal tension: they present tau2 as a cooling time while saying only the fast component is hot-carrier dynamics. That needs reconciling. The data repository link is a placeholder, which is not acceptable for a paper whose conclusions rest on raw TA traces. The electron/hole non-equivalence talk is speculative; the authors say 'further work is required,' so it's framed as a hypothesis, but it's promoted in the abstract as an outcome. That should be toned down.\n\nMy overall read: the qualitative bias-dependent trend is credible and worth publishing if the fits are shown to be robust against PIA contamination and the error bars are presented. I would not build my own numbers on these tau values yet, but I'd absolutely want to see the full analysis after revision.","headline":"Bias-resolved hot-carrier TA on a working perovskite cell is a real step forward, but the cooling-time numbers hinge on an admittedly 'qualitative' tail fit with no error bars; worth refereeing, not deserting.","tokens_in":13665,"tokens_out":1822,"would_cite":false,"duration_ms":19268,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Bias and illumination geometry control how fast hot carriers cool in an operating triple-halide perovskite solar cell, with current extraction shortening cooling times and open-circuit conditions preserving them.","keywords":["hot carriers","perovskite solar cells","transient absorption spectroscopy","carrier cooling","phonon bottleneck","thermalization dynamics","triple-halide perovskite","operating bias"],"falsifier":"The central claim would be falsified if, in a device where the extracted current is changed while the applied bias is held constant (by varying illumination intensity at fixed voltage), the carrier cooling times remained unchanged; that would show bias, not current extraction, controls thermalization. A simpler check is to measure cooling times on the same perovskite film without transport layers under an applied electric field: if the bias dependence disappears, the effect requires the full device interfaces, not the perovskite alone.","tokens_in":12678,"feed_emoji":"☀️","tokens_out":6022,"duration_ms":55070,"temperature":0.7,"pith_summary":"Hot carriers—high-energy electrons and holes created when a solar cell absorbs above-band-gap light—usually dump their excess energy as heat within picoseconds, and that loss is one of the biggest penalties in photovoltaics. This paper reports that in a working triple-halide perovskite solar cell, how fast those carriers cool is not fixed: it depends on the electrical operating point and on which side of the device the light enters. Using high-power transient absorption under biases matching short-circuit, maximum-power, and open-circuit conditions, the authors find that extracting current shortens the carrier cooling time, while open-circuit conditions keep the carriers hot longer. They also find that illumination through the front (hole-transport) side produces visibly hotter carrier distributions than illumination through the back (electron-transport) side. If correct, this means hot-carrier behavior measured on uncontacted films is only part of the story, and device-level operation must be included to know whether hot-carrier solar cells can actually work.","feed_headline":"Hot carriers cool faster when perovskite cell delivers power","feed_subtitle":"Bias and illumination side set carrier cooling times in working triple-halide perovskite solar cells.","key_machinery":"The central object is the carrier temperature Tc extracted from the high-energy tail of the transient absorption (TA) spectrum using a Maxwell-Boltzmann tail fit (Eq. 2), a standard readout for hot-carrier populations. This fit converts the slope of the TA tail into a single effective temperature at each pump-probe delay, and the time decay of Tc is then fit with a biexponential to yield two cooling times, τ1 (fast intraband relaxation) and τ2 (slow heat dissipation). The other load-bearing element is the device itself: a full triple-halide perovskite solar cell with transport layers, contacted and biased at Jsc, Vmax, and Voc, and illuminated from either the front (through the hole transport layer) or the back (through the electron transport layer). These choices let the authors separate material-level thermalization from device-level extraction and transport effects.","core_discovery":"The paper's central claim is that carrier thermalization in operational triple-halide perovskite (FA0.8Cs0.2Pb1.02I2.4Br0.6Cl0.02) solar cells is modulated by external bias and excitation geometry. Carrier temperatures Tc extracted from the high-energy tail of transient absorption spectra reach about 5000 K at 0.4 ps for the highest fluence (20 W/cm2), then relax through a fast component of 3–5 ps and a slower component of 10–120 ps. At high power, both cooling times are shorter when the cell is biased near short circuit (VJsc ≈ 0.02 V) or at the maximum power point (Vmax ≈ 0.8 V) than when the cell is left at open circuit with no extracted current; VJsc gives the shortest cooling time. Front-side illumination yields higher carrier temperatures than back-side illumination at the same fluence (e.g., ~4700 K vs ~3600 K at 0.4 ps and 20 W/cm2), which the authors attribute to greater absorption in the perovskite and a stronger carrier-density-dependent hot-phonon bottleneck. The paper interprets these results as a complex interplay among carrier density, field-assisted transport, extraction, and non-equivalent electron/hole thermalization in the full device architecture.","pith_inferences":["The paper's bias dependence suggests a design tension: hot carriers survive best near open circuit, but useful power is extracted near Vmax or short circuit, so a hot-carrier perovskite cell may need to slow cooling by other means (e.g., phonon engineering or selective contacts) rather than relying on operating point alone.","Because back-side illumination produces cooler carriers but longer cooling times, the published literature's hot-carrier numbers for perovskite solar cells likely mix different interfaces; comparing studies will require specifying illumination geometry as a standard parameter.","A clean test would be to vary the extracted current independently of the applied voltage (e.g., by tuning light intensity while holding bias fixed); if cooling times track extracted current rather than voltage, the extraction-driven phonon-bottleneck picture is confirmed.","If hot-carrier extraction is indeed more efficient when carriers stay hot longer, then electron- and hole-selective contacts with asymmetric hot-carrier collection could exploit the front/back asymmetry reported here."],"forward_implications":["At a device's maximum power point, current extraction measurably shortens hot-carrier cooling, so hot-carrier harvesting schemes must account for the operating bias, not just the absorber material.","Open-circuit conditions preserve hot carriers longer, meaning hot-carrier lifetime measurements on uncontacted films or at Voc overestimate the carrier populations available during power-producing operation.","Front-side vs back-side illumination changes both the peak carrier temperature and the cooling times, so reported hot-carrier parameters for a device depend on which interface the light enters.","The power dependence of the fast cooling component (longer τ1 at higher fluence) is consistent with a hot-phonon bottleneck that can be weakened by extracting carriers before they sustain the phonon population.","At high excitation, the maximum-power bias can even produce higher carrier temperatures at 0.4 ps than open circuit, indicating that early-time carrier-carrier interactions and band-gap renormalization are also bias-sensitive."],"supporting_citations":[{"why":"Supplies the triple-halide perovskite device architecture, fabrication, and high-temperature tolerance that make in-operando hot-carrier measurements possible.","marker":"[33]"},{"why":"Provides the hot-phonon bottleneck observation in lead-iodide perovskites that the paper uses to interpret power-dependent cooling times.","marker":"[15]"},{"why":"Establishes the transient-absorption tail-fitting approach for extracting hot-carrier temperatures in halide perovskites.","marker":"[21]"},{"why":"Provides prior evidence of hot-carrier extraction in metal halide perovskite solar cells, the device-level context this work extends.","marker":"[27]"},{"why":"Supplies the framework of hot-carrier cooling mechanisms in halide perovskites that underlies the two-component decay interpretation.","marker":"[34]"},{"why":"Supports the acoustic-optical phonon up-conversion and hot-phonon bottleneck mechanisms used to explain slow thermalization.","marker":"[37]"},{"why":"Earlier sub-stack measurements showing non-equivalent carrier dynamics in HTL/perovskite and ETL/perovskite structures, used to interpret front/back illumination differences.","marker":"[49]"}],"fun_headline_variants":["Bias speeds hot-carrier cooling in working perovskite cells","Perovskite solar cells cool hot carriers faster under load","Hot carriers chill faster when perovskite cells output power","Device bias tunes hot-carrier cooling in perovskite solar cells","Working perovskite cells cool hot carriers faster under bias"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the high-energy tail of the transient absorption signal is a faithful, linear measure of the hot-carrier distribution, so fitting it with a single Maxwell-Boltzmann temperature gives a true carrier temperature; if that tail is contaminated by other optical effects, the cooling times extracted from it would not describe carrier thermalization.","fun_headline_variants_meta":{"raw":{"variants":["Bias speeds hot-carrier cooling in working perovskite cells","Perovskite solar cells cool hot carriers faster under load","Hot carriers chill faster when perovskite cells output power","Device bias tunes hot-carrier cooling in perovskite solar cells","Working perovskite cells cool hot carriers faster under bias"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000445,"raw_usage":{"total_tokens":2307,"prompt_tokens":1058,"completion_tokens":1249,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":674,"completion_tokens_details":{"reasoning_tokens":1172}},"tokens_in":674,"tokens_out":1249,"duration_ms":8165,"temperature":1.0,"reasoning_tokens":1172,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T15:55:57.390193+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"The central claim would be falsified if, in a device where the extracted current is changed while the applied bias is held constant (by varying illumination intensity at fixed voltage), the carrier cooling times remained unchanged; that would show bias, not current extraction, controls thermalization. A simpler check is to measure cooling times on the same perovskite film without transport layers under an applied electric field: if the bias dependence disappears, the effect requires the full device interfaces, not the perovskite alone.","supporting_citations":[{"cited_title":"ACS Energy Letters, 2023","cited_arxiv_id":null,"evidence_quote":"Supplies the triple-halide perovskite device architecture, fabrication, and high-temperature tolerance that make in-operando hot-carrier measurements possible."},{"cited_title":"Nature Photonics, 2016","cited_arxiv_id":null,"evidence_quote":"Provides the hot-phonon bottleneck observation in lead-iodide perovskites that the paper uses to interpret power-dependent cooling times."},{"cited_title":"11(7): p","cited_arxiv_id":null,"evidence_quote":"Establishes the transient-absorption tail-fitting approach for extracting hot-carrier temperatures in halide perovskites."},{"cited_title":"Progress in Photovoltaics: Research and Applications, 2024","cited_arxiv_id":null,"evidence_quote":"Provides prior evidence of hot-carrier extraction in metal halide perovskite solar cells, the device-level context this work extends."},{"cited_title":"Nature communications, 2017","cited_arxiv_id":null,"evidence_quote":"Supplies the framework of hot-carrier cooling mechanisms in halide perovskites that underlies the two-component decay interpretation."},{"cited_title":"Nature communications, 2017","cited_arxiv_id":null,"evidence_quote":"Supports the acoustic-optical phonon up-conversion and hot-phonon bottleneck mechanisms used to explain slow thermalization."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Earlier sub-stack measurements showing non-equivalent carrier dynamics in HTL/perovskite and ETL/perovskite structures, used to interpret front/back illumination differences."}],"review_version":1}