<p>Parallel Prefix Adders (PPAs) are widely implemented in Quantum-dot Cellular Automata (QCA) owing to QCA technology’s high speed and scalability advantages. However, existing QCA-based PPA designs have largely emphasized minimizing area and delay, overlooking the true QCA-specific cost. As a result, several prior implementations have greatly altered circuit structures, increasing crossover complexity and overall QCA-specific cost. In this work, we present cost-efficient QCA implementations of PPAs by targeting and minimizing crossover-induced overhead. We first quantify the extensive use of crossovers in existing designs and their disproportionate contribution to QCA-specific cost. To address this issue, we perform a detailed, QCA-specific comparison of different PPA architectures, identifying the Sklansky and Ladner–Fischer adders as the most cost-effective architectures for QCA implementation. Based on this analysis, we propose compact, delay-aware 8-bit monolayer architectures for both adders, incorporating a clock-zone-based crossover scheme. To support scalability, we further propose cost estimation algorithms and extension techniques for implementing these designs at higher bit widths. The proposed designs achieve a 95% reduction in crossover complexity across 4, 8, and 16-bit configurations compared to the best prior designs. Furthermore, the proposed Sklansky adder reduces QCA cost by 37% at 4-bit, 61% at 8-bit, and 86% at 16-bit over the best prior design, with the proposed Ladner–Fischer adder achieving comparable gains. These results establish new benchmarks for scalable, cost-efficient and manufacturable QCA-based PPAs.</p>