Breaking the Shockley-Queisser (SQ) Limit to Develop a Next Generation of Solar Cell

<b>Abstract: </b>To overcome the well-known Shockley-Queisser (SQ) limit, one novel approach is to utilize the hot carrier generation and collection mechanism, which can achieve more than 67 % power conversion efficiency. A hot carrier is the photogenerated carrier above band gap, due to its extra energy difference between incident photon energy and optical band gap.[i] One signature of the hot carrier photovoltaic (PV) technology is a higher open-circuit voltage (V_OC) than the band gap of solar absorbers.<br/>However, hot carrier PV technology still suffers from the difficulty in collection of the ultra-short time scale hot carrier due to their rapid electron-phonon interaction. In the recent time, hybrid organic-inorganic based perovskite-based structure (e.g., APbX₃, where A = Cs, methylammonium (MA) or formamidinium (FA), X = (Cl, Br, I)) shows their capability in used as hot carrier solar cell due to their prolong carrier lifetime beyond 10s of picosecond or nanosecond, measured by the ultrafast pump-probe and time-resolved photoluminescence.[ii] However, all those characterizations not only investigated the perovskite thin films or solutions, rather than the solar cell working condition (i.e., <i>in-situ</i>), but also limited to the carrier diffusion mechanism, while the photocurrent obey the carrier drift understanding.<br/>Here lies some urgency to characterize the photocurrent within <i>in-situ</i> based perovskite solar cell (PSC) using a novel ultrafast photovoltaic spectroscopy to directly collect the photocurrent, when the solar cell at work.[iii] For the first time, with a sub - 40ps time resolution, we discover a transient V_OC much larger than the band gap of the mixed cation (CsMAFA) perovskite solar cells with &gt;20% efficiency. We further investigate the hot carrier drift transport property, which depends on film thickness and temperature.<br/><b>Keywords:</b> hot carrier, drift dynamics, charge collection, solar cell<br/><br/><br/>[i] Nozik, A. J. <i>et al.</i>, Semiconductor Quantum Dots and Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells. <i>Chem Rev</i> <b>2010</b>, 110, 6873-6890.<br/><br/>[ii] Wang, T. <i>et al.</i>, Protecting hot carriers by tuning hybrid perovskite structures with alkali cations. <i>Sci Adv</i> <b>2020</b>, 6, eabb1336.<br/><br/>[iii] Kobbekaduwa, K.; Liu, E.; Zhao, Q.; Bains, J. S.; Zhang, J.; Shi,Y.; Zheng, H.; Li, D.; Cai, T.; Chen, O.; Rao, A. M.; Beard, M.C.; Luther, J.M.; and Gao, J. Ultrafast Carrier Drift Transport Dynamics in CsPbI₃ Perovskite Nanocrystalline Thin Films. <i>ACS Nano</i><b> 2023</b>, 17, 13997–14004.