{"id":"3efa1a5b-e6a5-4bfc-a624-a1bdf51d8043","arxiv_id":"2607.25951","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"In paired simulations of 601 perovskite cell designs, mobile ions have only a small effect on the steady-state efficiency of efficient devices, with impact governed mostly by built-in voltage and hole lifetime.","lead":"Using simulations of 1202 paired perovskite cells, the authors compared devices with and without mobile ions and found that in efficient cells the ions barely change steady-state performance. This challenges the common assumption that ion migration itself is a main driver of efficiency loss, and it points to design rules based on built-in voltage and hole lifetime.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"SUI solver failures are non-random; the 601-pair complete-case analysis may exclude exactly the ion-sensitive efficient devices the conclusion is about.","rationale":"The reader's weakest assumption—that the 423 excluded pairs are missing sufficiently at random—is the same concern I identify as most load-bearing. The paper's own 'Numerical limitations' section admits the SUI failures are nearly all due to IonMonger's numerical design, which means missingness is a deterministic function of parameters, not a random process. The provided evidence (correlation convergence and DEI-PCE distribution similarity) does not test the missingness mechanism: convergence among included pairs says nothing about excluded regions, and comparing marginal DEI PCEs does not reveal whether the paired η for unsolved cases would differ. Moreover, the excluded DEI devices have slightly higher PCEs, aligning with the efficient-device regime highlighted in the abstract. If the unsolved SUI cases correspond to large V_bi and short τ_p—the parameters shown in Fig. 4 to produce the largest mobile-ion effects—then the complete-case p=0.10 could be a selection artifact. This does not prove the claim false, but it makes the headline conditional on a testable assumption, consistent with the reader's CONDITIONAL verdict. I therefore recommend no change to the verdict; the requested missing-data analysis and data availability would move it toward ACCEPT.","tokens_in":16187,"tokens_out":6580,"duration_ms":75716,"concrete_test":"Obtain the 423 unsolved SUI parameter sets and attempt to solve a stratified random sample (e.g., 100 sets) with relaxed IonMonger tolerances, finer/adaptive meshing, or an independent drift-diffusion code; for any remaining unsolved cases, use multiple imputation based on the DEI solution and the 32 design parameters. Then recompute the Brunner-Munzel test and the median paired ratio η over all 1024 pairs. If the p-value falls below 0.05 or the median |log η| shifts by more than 5%, the central claim fails; if the result is stable, the missing-data concern is resolved.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that mobile ions have no significant steady-state effect rests on 601 of 1024 factorial pairs. The 423 excluded pairs are nearly all SUI solver failures, and this missingness is not random: it is a deterministic consequence of IonMonger's numerical design, which is tuned for mobile-ion boundary layers. The paper's defenses are insufficient. The convergence of correlation coefficients (Fig. S1) is computed only on the included pairs; it cannot detect bias introduced by deleting entire regions of parameter space. The DEI-PCE comparison (Fig. S5) shows only that excluded devices have marginally higher DEI PCEs, not that their paired η=DEI/SUI would behave like the included ones. Since the abstract emphasizes efficient devices, and the excluded DEI devices skew toward higher PCE, the missing pairs may preferentially remove the very efficient-device cases the conclusion is about. If SUI failures concentrate at large V_bi and short τ_p—the parameters identified in Fig. 4 as controlling mobile-ion impact—the observed Brunner-Munzel p=0.10 could be an artifact of deleting the most ion-sensitive pairs. Until the missingness mechanism is modeled or the unsolved SUI cases are recovered, the headline 'no significant difference' is conditional on an untested assumption.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper uses the open-source drift-diffusion simulator IonMonger with a two-level fractional factorial design over 32 parameters to study how mobile ions affect steady-state solar-cell performance. For each parameter combination, the authors simulate a pair of devices—one with mobile ions (DEI) and one with immobile, uniformly distributed ions (SUI)—and compare their J-V characteristics. Of the 1024 parameter combinations sampled, only 601 yield solvable SUI cases, so the main analysis is based on those 601 complete pairs. The authors report that the DEI and SUI power-conversion-efficiency distributions are not significantly different (Brunner-Munzel p=0.10), that mobile ions tend to slightly reduce Jsc and increase Voc, and that a few poorly performing devices are strongly degraded by ions. They identify the built-in voltage Vbi and hole lifetime τp as the main moderators of ionic impact and propose a rational relationship between ΔV=Vbi−Vmpp and the ion-normalized PCE, from which they derive a design guideline (ΔV<0.27 V) for avoiding negative ionic effects.","tokens_in":16454,"tokens_out":4256,"duration_ms":40740,"significance":"If its central claim holds, the paper is a valuable counterweight to the common assumption that mobile ions necessarily degrade steady-state performance in perovskite solar cells. The study benefits from a well-motivated paired DEI/SUI design, literature-based parameter ranges, and a careful verification that the ultra-slow J-V scans approximate true steady state (reported deviation at MPP is 2.0×10−6% on average). The use of a published open-source model and transparent statistical reporting (Brunner-Munzel test, Bonferroni correction) are additional strengths. However, the headline population comparison and the abstract's more specific claim about efficient devices are both conditional on a substantial, potentially informative missing-data mechanism: 423 of 1024 SUI simulations failed to solve. The paper's own convergence diagnostic is computed only on the included pairs, so it cannot detect bias from deleting entire regions of parameter space. The efficient-device subclaim is also not supported by a dedicated statistical test. For these reasons, the significance of the paper depends on whether the missingness is addressed.","major_comments":[{"comment":"The central comparison relies on 601 of 1024 parameter pairs because 423 SUI simulations failed, almost all failures being SUI. The paper argues the remaining pairs are sufficient because correlation coefficients converge (Fig. .1) and because excluded DEI devices have a similar PCE distribution, with a slightly higher mean and smaller variance (Fig. .5). Neither of these checks addresses the missingness mechanism. If SUI non-convergence is more likely for large Vbi and short τp—the parameters that Fig. 4A identifies as the strongest moderators of ion-normalized PCE—then the complete-case sample underrepresents precisely the devices in which mobile ions have the largest negative effect. The convergence of correlations on the included pairs cannot detect this selection bias, and Fig. .5 reports only DEI PCE, not the paired DEI/SUI ratio. The paper should analyze the missingness as a funct","section":"Numerical limitations; Figure .5; Figure 4A"},{"comment":"The abstract's headline claim is that 'in efficient devices, mobile ions have only a small impact on steady-state performance.' The statistical test reported (Brunner-Munzel p=0.10) is applied to the entire 601-device population, not to the efficient-device subset. Figure 2A shows visually that points with SUI PCE > 15% cluster near the y=x line, but no quantitative analysis of this subset is given (e.g., the fraction of efficient devices with |η~−1| > 10%, or a test comparing efficient vs. inefficient devices). Given the paper's emphasis on efficient devices, the authors should either restrict the B-M test (or an equivalent paired analysis) to the efficient-device group, or explicitly state that the population-level result is what supports the conclusion, with the efficient-device statement being a qualitative observation.","section":"Impact of Mobile Ions on Steady State Power Conversion; Figure 2A"},{"comment":"Equations (9) and (10) are presented as predictions, but they are algebraic rearrangements of the four fitted constants a–d in Eq. (8). Specifically, Eq. (9) solves Eq. (8) for ΔV at η~=1, and Eq. (10) is the limit a/c. These do not constitute independent predictions; their validity is entirely inherited from the quality of the fit, which has R²=0.65 and for which no confidence intervals are reported. The statement that a device with ΔV<0.27 V will have 'neutral or positive impact' is therefore an extrapolation from a moderate-correlation fit, not a derived design rule. The authors should present uncertainty bounds on a/c and the ΔV|η~=1 crossing, and ideally validate the rational function on a holdout sample of the same parameter space.","section":"Bias at MPP strongly influences mobile ion impact; Eqs. 8–10"}],"minor_comments":[{"comment":"The sentence 'Our results suggest (§ & § ) it is for less efficient devices...' contains unresolved section references ('§ & §'). Please replace with actual section numbers or remove.","section":"Conclusions"},{"comment":"The caption says the VMPP is held static for '1×10−5s', while the main text says '1×10^5 s'. These differ by ten orders of magnitude; please correct the typo.","section":"Figure .2 caption"},{"comment":"There are several typos and minor grammatical errors, e.g., 'a abd physics audience' in the Results section, 'through literature review' in the Conclusions, and inconsistent use of SI figure labels ('Figure .1', etc.). A careful proofread is needed.","section":"Throughout"},{"comment":"Some parameters in Table 1 (β, Auger coefficient) are listed with 'N/A' high/low values, meaning they are fixed rather than varied. This is acceptable, but the table would be clearer if a separate column indicated which parameters are varied in the factorial design and which are fixed.","section":"Table 1"},{"comment":"The B-M p-value is reported in the text but not in Figure 2C. Adding the p-value and the test name directly to the figure panel would improve transparency.","section":"Statistical reporting"}],"recommendation":"major_revision","confidential_remarks":"The main obstacle to acceptance is the informative missingness in the SUI arm. The authors have been transparent about the 601/1024 completion rate, but their numerical-limitations defense is not sufficient: convergence on included pairs and similar DEI PCE distributions do not establish that the missing pairs would behave like the included ones, especially if failures concentrate in the high-Vbi/short-τp regime that the paper itself identifies as ion-sensitive. I would be willing to accept after the authors either recover the SUI solutions, model the missingness, or substantially temper the central claim. The overstatement of Eqs. (9)–(10) as predictions is also in need of revision. The paper is otherwise careful and would be a useful contribution if these points are addressed."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear [Colleague],\n\nThis one is worth your time. Cowley et al. run paired drift-diffusion simulations: each device is simulated with mobile ions (DEI) and with immobile uniform ions (SUI), across a 32-parameter two-level factorial design. They end up with 601 solved pairs. The headline result is that the DEI and SUI PCE distributions are statistically indistinguishable (Brunner-Munzel p=0.10), and that ions move efficiency by at most ±10% for most devices. The design rule—keep ΔV = V_bi − V_mpp below about 0.27 V—is actionable and likely to be cited.\n\nThe paper does several things well. The steady-state check is careful: an ultra-slow JV scan is verified against 1e5 s MPP holds with tiny deviations. The parameter ranges are literature-based. The authors are honest about the numerical failures, reporting that 423 pairs were dropped because the SUI case would not solve. Using IonMonger is legitimate; it is published open-source.\n\nThe soft spots are real. The missing 423 pairs are nearly all SUI non-convergences, and missingness is probably not random: IonMonger is numerically tuned for mobile-ion boundary layers, so the SUI solver will fail preferentially in certain parameter regimes. The paper's defense—correlation coefficients converge after ~600 samples, and excluded DEI devices look similar—addresses the marginal DEI distribution, not the paired ion-sensitivity of the missing cases. If SUI failures concentrate at large V_bi and short hole lifetime, the exact parameters that Fig. 4 identifies as controlling mobile-ion impact, then the \"no significant difference\" could be an artifact of deleting the most ion-sensitive pairs. That needs a missing-data analysis or a solver fix.\n\nTwo smaller issues. First, the B-M test is unpaired; with paired data a paired test would have more power, so the null result is weaker than it looks. Second, Eqs. 9 and 10 are algebraic rearrangements of the four-constant rational fit in Eq. 8 (R²=0.65), not independent predictions; the \"ΔV < 0.27 V\" rule is a heuristic from a noisy fit, not a law.\n\nNo code or data are shipped, so exact reproduction isn't possible. That should be fixed.\n\nWho is this for? Experimentalists and modellers working on ion migration in perovskites. It deserves a serious referee, but with major revision: address the missing-data mechanism, run paired tests, and deposit the simulation outcomes.\n\nBest.","headline":"A serious paired simulation study arguing that mobile ions have little steady-state effect in efficient perovskite cells; the headline claim is plausible but rests on a non-random missing-data mechanism that the paper does not model.","tokens_in":16955,"tokens_out":3788,"would_cite":true,"duration_ms":36564,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Mobile ions have only a small effect on the steady-state efficiency of efficient perovskite solar cells, and the effect can be positive or negative.","keywords":["mobile ions","perovskite solar cells","steady-state performance","drift-diffusion simulation","design of experiments","field screening","built-in voltage","hole lifetime"],"falsifier":"Solve the full 1024-pair design with a fixed-ion solver that does not fail on the previously excluded cases and check whether any efficient (SUI PCE > 20%) and high-ion-density pair shows a DEI/SUI PCE ratio outside the paper's observed range; alternatively, in experiment, build two otherwise identical cell sets differing only in ion density (e.g., by halide-vacancy concentration) and measure steady-state MPP; a >10% systematic difference would refute the claim.","tokens_in":16062,"feed_emoji":"☀️","tokens_out":4775,"duration_ms":44746,"temperature":0.7,"pith_summary":"Using drift-diffusion simulations, the paper compares 601 pairs of perovskite solar cells that are identical in every material parameter except that in one member of each pair the ions are mobile and in the other they are fixed and uniformly distributed. The headline result is that the efficiency distributions of the two populations cannot be statistically distinguished (p = 0.10), and that for efficient cells the presence of mobile ions changes steady-state efficiency by only a few percent relative, with roughly equal numbers of devices helped and hurt. The paper concludes that ion migration is not automatically the main cause of steady-state efficiency loss, and identifies built-in voltage and hole lifetime as the parameters that decide whether mobile ions are neutral, beneficial, or harmful.","feed_headline":"Mobile ions have little effect on steady-state perovskite efficiency","feed_subtitle":"A 601-pair simulation study finds no statistical difference in output between cells with and without ionic motion.","key_machinery":"The central tool is paired-device drift-diffusion simulation: for each parameter set, one cell has mobile ions (DEI) and an otherwise identical cell has fixed uniformly distributed ions (SUI). The ion-normalized ratio of each J-V metric isolates the ion effect. A two-level fractional factorial design samples the 32-parameter space, with convergence checks and a non-parametric heteroscedastic test supporting the statistical claims. The mechanism is field screening: ions accumulate at interfaces and screen the built-in field, quantified by ΔV = Vbi − Vmpp, and the paper fits a rational function to predict when screening is harmful or helpful.","core_discovery":"The paper argues that, at steady state, mobile ions are not inherently harmful in efficient perovskite solar cells. Across 601 pairs of simulated devices identical except for whether ions can move, the power-conversion efficiency distributions of the mobile-ion and immobile-ion sets cannot be distinguished statistically (p = 0.10). The same pairing shows that most devices fall within ±10% efficiency change, poor devices are often made worse, some devices are improved, and the key determinants of harm are a large built-in voltage relative to the maximum-power-point voltage and a short hole lifetime.","pith_inferences":["Editorial inference: If the conclusion transfers to real cells, then efforts to suppress ion migration (e.g., via additives or grain-boundary passivation) may not improve steady-state efficiency as much as assumed; their benefit may lie mainly in stabilising dynamic behaviour and preventing chemical degradation.","Editorial inference: The paired-design methodology could be applied to other slow processes (e.g., trap filling or thermal effects) that also alter steady-state J-V curves, using the same ratio statistics.","Editorial inference: A direct experimental test would compare steady-state MPP efficiency of two cell types with identical optoelectronic parameters but differing ionic mobility—for example by temperature or composition—and check whether PCE differences track the paper's ΔV threshold."],"forward_implications":["Efficient devices (SUI PCE > 20%) are minimally affected by mobile ions even at ion densities of 1e19 cm^-3, so high ion concentrations do not necessarily preclude high steady-state efficiency.","Devices with poor steady-state performance (<15% PCE) are made worse by mobile ions in rough proportion to their underperformance.","A large built-in voltage relative to the maximum-power-point voltage (ΔV = Vbi − Vmpp) is the main predictor of ion-induced harm; keeping ΔV below about 0.27 V should make mobile ions neutral or mildly beneficial.","Longer hole lifetimes reduce the impact of ion field screening, so improving bulk recombination resilience is a design lever against ion effects.","Because the no-difference result is a failure to reject the null, it does not prove equivalence; the paper frames it as showing the effect is not statistically detectable within the studied parameter range."],"fun_headline_variants":["Ion motion barely moves perovskite steady-state efficiency","Simulation: mobile ions don't hurt efficient perovskite cells","601 simulated pairs: ionic motion is a wash for perovskite efficiency","Mobile ions: little steady-state impact on efficient perovskite cells","In efficient perovskites, mobile ions have negligible steady-state effect"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The load-bearing premise is that the 423 device pairs excluded because the fixed-ion simulation did not solve are missing at random; if those cases systematically fall in the regimes where mobile ions matter most, the 'no significant difference' conclusion would not hold.","fun_headline_variants_meta":{"raw":{"variants":["Ion motion barely moves perovskite steady-state efficiency","Simulation: mobile ions don't hurt efficient perovskite cells","601 simulated pairs: ionic motion is a wash for perovskite efficiency","Mobile ions: little steady-state impact on efficient perovskite cells","In efficient perovskites, mobile ions have negligible steady-state effect"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000147,"raw_usage":{"total_tokens":978,"prompt_tokens":656,"completion_tokens":322,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":400,"completion_tokens_details":{"reasoning_tokens":241}},"tokens_in":400,"tokens_out":322,"duration_ms":3163,"temperature":1.0,"reasoning_tokens":241,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T01:00:29.492769+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Solve the full 1024-pair design with a fixed-ion solver that does not fail on the previously excluded cases and check whether any efficient (SUI PCE > 20%) and high-ion-density pair shows a DEI/SUI PCE ratio outside the paper's observed range; alternatively, in experiment, build two otherwise identical cell sets differing only in ion density (e.g., by halide-vacancy concentration) and measure steady-state MPP; a >10% systematic difference would refute the claim.","supporting_citations":[],"review_version":1}